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Prospects of Dorycnium species to increase

water use in agricultural systems of southern

Australia

Lindsay William Bell

B. Agr. Sc. – Plant and Soil Science (Hons. Class 1), University of Queensland

This thesis is presented for the degree of Doctor of

Philosophy of The University of Western Australia,

School of Plant Biology

November 2005

ii

Hairy Canary,

how do you vary,

and where do your flowers grow?

How do you taste,

and grow with more haste,

to halt the salinity flow?

iii

Summary

Dryland salinity is a major environmental challenge facing agriculture in Australia. One

option to manage dryland salinity is the use of perennial forages that increase water use

of agricultural systems. However, the current array of perennial forages is limited.

Forage species that satisfy the range of climatic and edaphic environments, and

production systems, in southern Australia are needed (Chapter 1). In particular, low

rainfall regions lack options other than lucerne (Medicago sativa L.) (Chapter 1). The

Dorycnium genus (canary clovers) contains perennial species that might be useful

forage plants for southern Australia. Dorycnium are sub-shrubs and their plant form

differs from current perennial forages (Chapter 1). The aim of this project was to

investigate some of the agronomic traits of several species of the genus Dorycnium to

explore where they might be used in Australia and how they might be integrated into

agricultural systems for management of dryland salinity.

First, two desktop investigations assessed the potential adaptation and role of

Dorycnium species in southern Australia: a review of the current literature on the

agronomic characteristics of Dorycnium (Chapter 2) and an eco-geographical analysis to

explore the ecology of Dorycnium species (Chapter 3). The agronomy of Dorycnium

has been previously researched mainly in New Zealand, and although this provides

some indications on where and how Dorycnium might be best used in Australia, this

still requires testing in Australia. In particular, the aluminium tolerance of Dorycnium

species indicates that they may be more suitable for acid soils than lucerne. Little

ecological data was obtained for germplasm and herbarium collection sites of

Dorycnium species. Climate comparisons between the native distribution of Dorycnium

species in the Mediterranean basin and Australia, using spatial aridity data and

CLIMEX climate match modelling, revealed that D. hirsutum and D. rectum might be

suitably adapted to the temperate pasture regions of southern Australia. Suitable

germplasm of D. pentaphyllum may also exist, but subsequent investigations in this

project focussed on D. hirsutum and D. rectum.

The potential of Dorycnium to increase water use was assessed in two field experiments

in the wheatbelt of Western Australia (Chapter 4). Soil water dynamics were compared

over 3 years under D. hirsutum-, lucerne- and annual legume-based pastures. Soil under

D. hirsutum was drier than annual pastures by 8-23 mm more in year 1, 43–57 mm in

iv

year 2 and 81 mm in year 3. D. hirsutum extracted water from the soil in a similar

manner to lucerne.

Establishment and summer survival of D. hirsutum and D. rectum were also

investigated at a range of locations in the wheatbelt of Western Australia (Chapter 5).

This revealed that Dorycnium were slow to establish and that D. hirsutum survival was

superior to D. rectum. Establishment techniques to remove weed competition, such as

delaying sowing until after effective weed control, could improve establishment

reliability.

Two glasshouse experiments investigated possible reasons for slow early growth and

establishment in Dorycnium and the reasons for differences in survival observed

between D. hirsutum and D. rectum (Chapters 6 and 7). These suggested that slow

emergence contributes to the slow early vigour of Dorycnium. It was also found that D.

hirsutum produced deep roots more quickly than D. rectum and possessed a number of

physiological and morphological attributes that suggested it was better adapted to more

arid conditions.

To gain some indication of the grazing management required for D. hirsutum and D.

rectum the effect of cutting height on production and nutritive value was investigated in

an irrigated field experiment near Perth (Chapter 8). Intense defoliation at intervals ≤ 8

weeks was not suitable for Dorycnium species. However, if left uncut, plants

accumulated a large amount of woody stem. Nutritive value of D. rectum was higher

than D. hirsutum, but it was lower in both species than for lucerne.

In conclusion, Dorycnium show promise as new perennial forages in southern Australia.

D. rectum could be used in alleys in higher rainfall permanent pasture systems. D.

hirsutum is tolerant of low rainfall environments and might be used as a component of

permanent pastures in conditions unsuitable for crops, in long-term rotations with crops,

or possibly, intercropping systems. The genetic variation in key agronomic traits, such

as forage quality, seedling vigour and acid soil tolerance, require investigation before

further development of Dorycnium should occur.

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Table of contents

Summary .......................................................................................................iii Table of contents ............................................................................................v Statement of candidate contribution ..............................................................x

Acknowledgements .......................................................................................xi Publications arising from this thesis ............................................................xii

Chapter 1: Introduction – Fitting perennial forages in agricultural systems to manage dryland salinity in southern Australia: a review...........................1

ABSTRACT.......................................................................................................................1

INTRODUCTION................................................................................................................2

THE CAUSES OF DRYLAND SALINITY................................................................................3

IMPACTS OF DRYLAND SALINITY .....................................................................................3

SALINITY MANAGEMENT OPTIONS ...................................................................................5

PERENNIAL FORAGE OPTIONS IN A VARIABLE AGRICULTURAL REGION............................7

Agro-climatic zones....................................................................................................7

Climatic constraints .................................................................................................10

Edaphic constraints..................................................................................................11

Economic and management constraints ..................................................................16 SYSTEMS FOR PERENNIAL FORAGES..............................................................................17

Monocultures vs mixed systems ...............................................................................17

Permanent pastures..................................................................................................17

Integration with crops..............................................................................................18

Systems for alternative plant types...........................................................................25 LIVESTOCK PRODUCTION CONSIDERATIONS..................................................................26

CONCLUSION.................................................................................................................28

RESEARCH OBJECTIVES.................................................................................................30

REFERENCES.................................................................................................................30

Chapter 2: The potential of Dorycnium as a forage plant to manage water in the landscape: a review of its agronomic characteristics.........................39

ABSTRACT.....................................................................................................................39

INTRODUCTION..............................................................................................................40

TAXONOMY AND DISTRIBUTION ....................................................................................41

DESCRIPTION OF DORYCNIUM SPECIES...........................................................................43

PLANT IMPROVEMENT ...................................................................................................45

AGRONOMIC FACTORS AFFECTING THE POTENTIAL OF DORYCNIUM...............................45

Adaptation................................................................................................................46

Establishment ...........................................................................................................47

Biomass production..................................................................................................48

Grazing management ...............................................................................................50

Nitrogen fixation ......................................................................................................50

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CONSIDERATIONS FOR ANIMAL PRODUCTION................................................................51

Forage value ............................................................................................................51

Condensed tannins ...................................................................................................53

Other anti-nutritional compounds ...........................................................................55

Palatability...............................................................................................................56 CONCLUSION AND FUTURE RESEARCH AREAS...............................................................56

REFERENCES.................................................................................................................57

Chapter 3: Germplasm collections, eco-geography and climate match modelling to southern Australia for Dorycnium species..............................63

ABSTRACT.....................................................................................................................63

INTRODUCTION .............................................................................................................64

MATERIALS AND METHOD.............................................................................................66

Germplasm collections.............................................................................................66

Collection sites of Dorycnium taxa..........................................................................66

Climate aridity comparisons....................................................................................66

Climate match modelling .........................................................................................67 RESULTS.......................................................................................................................68

Germplasm collections.............................................................................................68

Collection sites of Dorycnium taxa..........................................................................68

Climate aridity comparisons....................................................................................71

Climate match modelling .........................................................................................73 DISCUSSION..................................................................................................................77

REFERENCES.................................................................................................................78

Chapter 4: Comparative water use by Dorycnium hirsutum-, lucerne- and annual-based pastures in the Western Australian wheatbelt ........................81

ABSTRACT.....................................................................................................................81

INTRODUCTION .............................................................................................................82

MATERIALS AND METHOD.............................................................................................83

Site description and history .....................................................................................83

Experimental design.................................................................................................84

Site preparation and management ...........................................................................85

Plant density.............................................................................................................85

Biomass production .................................................................................................86

Soil water measurements .........................................................................................86

Statistical analysis ...................................................................................................87

RESULTS.......................................................................................................................88

Environmental conditions ........................................................................................88

Plant density.............................................................................................................88

Biomass production .................................................................................................90

Soil water dynamics .................................................................................................92 DISCUSSION..................................................................................................................96

CONCLUSIONS...............................................................................................................98

vii

REFERENCES.................................................................................................................98

Chapter 5: Establishment and summer survival of Dorycnium hirsutum and D. rectum in Mediterranean environments..........................................101

ABSTRACT...................................................................................................................101

INTRODUCTION............................................................................................................102

MATERIALS AND METHOD...........................................................................................103

Experiment 1: Species and summer survival .........................................................103

Experiment 2: Time of sowing ...............................................................................104

Statistical analysis..................................................................................................105 RESULTS.....................................................................................................................106

Experiment 1: Species and summer survival .........................................................106

Experiment 2: Time of sowing ...............................................................................110 DISCUSSION................................................................................................................114

Species differences .................................................................................................114

Survival strategies..................................................................................................115

Plant size effects.....................................................................................................115

Management implications ......................................................................................116 CONCLUSIONS.............................................................................................................117

REFERENCES...............................................................................................................117

Chapter 6: Relative growth rate, resource allocation and root morphology in the perennial legumes, Medicago sativa, Dorycnium rectum and D. hirsutum grown under controlled conditions .............................................121

ABSTRACT...................................................................................................................121

INTRODUCTION............................................................................................................122


Experimental design...............................................................................................123

Sampling procedure and measurements ................................................................124

Experimental conditions ........................................................................................125

Statistical analysis..................................................................................................125 RESULTS.....................................................................................................................126

Growth factors .......................................................................................................126

Resource allocation................................................................................................129

Root depth ..............................................................................................................131

Root growth and distribution .................................................................................132 DISCUSSION................................................................................................................133

Growth factors .......................................................................................................133

Resource allocation................................................................................................138

Root depth and distribution....................................................................................138 CONCLUSIONS.............................................................................................................139

REFERENCES...............................................................................................................139

viii

Chapter 7: Water relations and adaptations to increasing water deficit in three perennial legumes, Medicago sativa, Dorycnium hirsutum and D. rectum.........................................................................................................143

ABSTRACT...................................................................................................................143

INTRODUCTION ...........................................................................................................144

MATERIALS AND METHOD..........................................................................................145


Physiological measurements..................................................................................148

Pressure-volume relationship ................................................................................149

Recovery after drought ..........................................................................................149

Statistical analysis .................................................................................................149 RESULTS.....................................................................................................................149

Plant water status ..................................................................................................149

Osmotic adjustment................................................................................................152

Photosynthetic responses .......................................................................................153

Pressure-volume curves .........................................................................................155

Leaf morphological adaptations ............................................................................157

Recovery after drought ..........................................................................................158 DISCUSSION................................................................................................................158

Physiological adaptations......................................................................................158

Morphological adaptations....................................................................................160 CONCLUSIONS.............................................................................................................161

REFERENCES...............................................................................................................161

Chapter 8: Production, survival and nutritive value of the perennial legumes Dorycnium hirsutum and D. rectum subjected to different cutting heights.........................................................................................................165

ABSTRACT...................................................................................................................165

INTRODUCTION ...........................................................................................................166



Measurements of nutritive value............................................................................170

Statistical analysis .................................................................................................171 RESULTS.....................................................................................................................171

Plant survival and DM production ........................................................................171 Nutritive value........................................................................................................177

DISCUSSION................................................................................................................181

Total DM production and plant survival ...............................................................181

Nutritive value........................................................................................................182

Practical implications............................................................................................184 REFERENCES...............................................................................................................185

Chapter 9: General discussion ..................................................................189

INTRODUCTION ...........................................................................................................189

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POTENTIAL ECOLOGICAL SCOPE FOR DORYCNIUM.......................................................189

MATCHING DORYCNIUM WITH FARMING SYSTEMS.......................................................191

FUTURE RESEARCH AND DEVELOPMENT REQUIREMENTS.............................................194

REFERENCES...............................................................................................................196

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Statement of candidate contribution

The research presented in this thesis is an original contribution to the field of pasture

science. The hypotheses and experiments presented and discussed herein are my

original ideas and writing. Others that have made important contributions to this

research are recognized in the acknowledgements and when appropriate in the published

papers arising from this work.

Lindsay Bell

November 2005

xi

Acknowledgements

For their supervision of my PhD project I would especially like to thank Dr Mike

Ewing, Dr Megan Ryan, Dr Sarita Bennett, Geoff Moore and Professor Phil Cocks,

their advice and time has been greatly appreciated. Thanks must go to the CRC for

Plant-based Management of Dryland Salinity, Jean Rogerson Memorial Trust, and to

the AW Howard Memorial Trust for providing me with a stipend.

For their assistance I would like to thank Department of Agriculture Staff; Darryl

McClements, Ross Thompson and Chris Gadja for their help installing neutron access

tubes; John Tittrington, Brad Wintle and Tony Albertson for help sowing the trials,

carrying out herbicide and pesticide applications and for conducting plant survival

measurements at Katanning and Bibby Springs; and staff at Merredin and Medina

Research Stations. I am grateful to Ian Wright for allowing me to conduct field

experiments on his property and the staff at CSIRO Livestock Industries in Perth,

especially Dr Hayley Norman, Dr David Henry, Dr David Masters, Elizabeth Hulm and

Lesley Store, for their guidance during nutritive value analysis. Thanks to Eric Hall,

Tasmanian Institute of Agricultural Research, and the Trifolium Genetic Resource

Centre, Department of Agriculture Western Australia for providing the seed used during

my experiments.

Special thanks to my fellow post-graduate students and others at the School of Plant

Biology and in the CRC for Plant-based Management of Dryland Salinity who have

helped me out over the past few years. In particular for their input I would like express

my gratitude to: Richard Bennett for his assistance in the field and with ArcGIS

software; Aleida Williams for her assistance conducting measurements in the field and

also her help, advice and comments on the two glasshouse studies; Claire Farrell for her

assistance with field trials and all that jazz; Rob Creasy for glasshouse assistance; and

Mohammed Ali Bhatti for help taking DM cuts.

I appreciate the comments on the chapters in this thesis from Professor Hans Lambers,

Dr Erik Veneklaas, Professor David Turner, Perry Dolling, Dr Chris Davies, Aleida

Williams and Dr Hayley Norman.

Finally, I would like to thank my lovely wife Alison for following me over to Perth and

supporting me during this undertaking.

Cheers and bottoms up!

xii

Publications arising from this thesis

Bell LW, Ewing MA, Ryan MH (submitted) Fitting perennial forages into agricultural

systems to manage dryland salinity in southern Australia: a review. Agricultural

Systems. (Chapter 1)

Bell LW, Bennett RG, Ryan MH, Moore GA, Ewing MA and Sarita J. Bennett

(submitted) Germplasm collections, eco-geography and climate match modelling to

southern Australia for Dorycnium species (canary clovers). Plant Genetic Resources

Newsletter. (Chapter 3)

Bell LW, Moore GA, Ryan MH, Ewing MA (submitted) Comparative water use by

Dorycnium hirsutum-, lucerne- and annual-based pastures in the Western Australian

wheatbelt. Australian Journal of Agricultural Research. (Chapter 4)

Bell LW, Moore GA, Ewing MA, Bennett SJ (2005) Establishment and summer

survival of the perennial legumes, Dorycnium hirsutum and D. rectum in Mediterranean

environments. Australian Journal of Experimental Agriculture 45, 1245-1254. (Chapter

5)

Bell LW (2005) Relative growth rate, resource allocation and root morphology in the

perennial legumes, Medicago sativa, Dorycnium rectum and D. hirsutum grown under

controlled conditions. Plant and Soil 270, 199-211. (Chapter 6)

Bell LW, Williams A, Ryan MH, Ewing MA (submitted) Water relations and

adaptations to increasing water deficit in three perennial legumes, Medicago sativa,

Dorycnium hirsutum and D. rectum. Environmental and Experimental Botany (Chapter

7)

Bell LW, Moore GA, Ewing MA, Ryan MH (2006) Production, survival and nutritive

value of the perennial legumes Dorycnium hirsutum and D. rectum subjected to

different cutting heights. Grass and Forage Science 61, 60-70. (Chapter 8)

Chapter 1: Introduction – Fitting perennial forages in agricultural

systems to manage dryland salinity in southern Australia: a

review

Abstract

The sustainability of agricultural production in southern Australia is threatened by

dryland salinity. The integration of perennial forages into agricultural systems provides

an opportunity to maintain production and profit whilst increasing water use. A suite of

perennial forage species that satisfy the range of climatic and edaphic environments and

production systems in southern Australia is needed. This chapter reviews the major

climatic, edaphic, management and economic limitations to the current array of

perennial forage options, describes possible farming systems that facilitate incorporation

of perennial forages and, finally, suggests plant traits that would be valuable in these

systems.

Currently the majority of commercial perennial forages in Australia are best suited to

permanent pasture systems in regions with mild temperatures and high rainfall, where

persistence and productivity are not impeded by periods of severe water deficit. In lower

rainfall environments, where cropping predominates, lucerne (Medicago sativa L.) is

the most prominent option. Lucerne, in a pasture phase, extracts water from the sub-soil

creating a dry soil ‘buffer’, which is then refilled during a cropping phase enabling

groundwater recharge to be reduced whilst integrating crops with perennial forages.

Alley farming and intercropping also provide opportunities for perennial forages to be

integrated with crop production. In situations where cropping is least profitable (e.g.

infertile or saline soils), permanent pastures tolerant of these stresses may be

economically justified.

A greater variety of perennial forages than currently available is required for the range

of salinity threatened environments and to provide diversity within each setting. Few

alternatives currently exist. In particular, acid or waterlogged soils in low rainfall

regions are currently poorly served with options. In addition to being adapted to these

conditions, new species need to satisfy the agronomic requirements of the systems in

which they are likely to fit. A range of potentially useful plant types have been

Chapter 1: Fitting perennial forages into agricultural systems 2

identified for which the farming systems are not well defined. The agronomic

characteristics of these species need to be assessed and, possibly, new systems designed

that allow these species to attain their full productive potential.

Introduction

Secondary dryland salinity can be defined as human-induced salinisation in non-

irrigated areas. Worldwide there are large areas of salt-affected land associated with

irrigation, but Australia possesses the great majority of salt-affected land in dryland

regions (Ghessemi et al. 1995). Management of dryland salinity will require the

development and implementation of a combination of tools including engineering and

plant-based options. A major challenge is to replace current annual-based agricultural

systems with perennials that can restore pre-clearing hydrology. Within the possible

plant solutions, there are two key approaches. An empirical approach involves

investigating a large number of plants and identifying those with productivity and

persistence potential in the target environment. Armed with these plants it becomes

possible to identify systems within which they can be used. An alternative approach is

to analyse which systems are likely to be profitable and then seek the perennial plants

that might be suited to each system. Thus, there are plants looking for places and places

looking for plants.

This chapter will focus on the use of deep-rooted perennial forages that would enable

livestock production to continue while addressing sustainability concerns. Other authors

have previously reviewed the current use and future potential of a range of perennial

legumes (Bennett 2002; Dear et al. 2003), grasses (Reed 1996; Oram and Lodge 2003)

and forage shrubs and trees (Lefroy 2001). This review will begin by briefly describing

the causes of dryland salinity, its main impacts in Australia and the scale and economy

needed to overcome the problem. Climatic, edaphic, economic and management

constraints to current perennial forage options will be outlined, some likely systems in

which new species will fit and the plant traits that might best suit these situations. Some

alternative plant types that have potential, and livestock production considerations, will

also be discussed.

3

The causes of dryland salinity

Australian soils have naturally high levels of salt which has been carried inland from the

ocean by rainfall and dust over thousands of years (Hingston and Gailitis 1976) to

accumulate at high levels in sub-soils (e.g. in Western Australian soils, 100–15 000 t

salt/ha have been measured) (McFarlane and George 1992). Until European settlement,

200 years ago, this salt remained ‘inert’ below the rooting zone of the vegetation.

However, the widespread clearing of the deep-rooted perennial native vegetation for

agricultural development and its replacement with shallow-rooted annual crops and

pastures disrupted the long-term hydrological balance (Hatton et al. 2003).

Additional water leached past the roots of the annual plants and into groundwater tables

causing them to rise. The rising groundwater table mobilised salt stored deep in the soil

and brought salt to the surface (Fig. 1). This ‘discharge zone’ typically occurs on the

valley floors. An increase in surface water run-off onto and through valley floors also

amplified recharge to the groundwater table in the discharge zone and lower parts of the

landscape (Hatton et al. 2003). Recharge of groundwater tables on the slopes and ridges

(‘recharge zone’) provided an additional hydraulic gradient, forcing groundwater

towards the valley floors (Hatton et al. 2003).

Impacts of dryland salinity

The National Land and Water Resources Audit (2001) estimated that over 4.7 million

hectares of land in Australia is currently affected by dryland salinity and that this area

could expand to 13.6 million ha by 2050. In Western Australia, which has the largest

area at risk, as much as 30% of the agricultural land may be affected. Recently, the

validity of these figures has been questioned, because water table depth was used as an

indicator of salinity hazard and this may have overestimated the threatened area.

Subsequently, McFarlane et al. (2004) assessed that about 1 million ha of land in

Western Australia is currently salt-affected, compared to the 3.54 million ha stated by

the National Land and Water Resources Audit (2001). Despite this disagreement over

the extent of the affected area, the evidence is clear that the impact of dryland salinity is

large and will continue to increase.


Figure 1. The changes to groundwater levels from the native situation (top) to the current

situation (bottom). In the current situation, in the recharge zone, shallow rooted annual plants

allow excess water to drain into groundwater tables causing them to rise and bring saline

groundwater to the surface in the valley floors (discharge zones) (adapted from Walker et al.

(1999)).

In addition to the costs of salinity in terms of lost agricultural land and production, even

larger costs will be incurred due to impacts on:

1) Building, rail and road infrastructure. By 2050, 67 000 km of road, 5 100 km of

rail and 220 towns will be at risk from shallow saline watertables (National Land

and Water Resources Audit 2001).

2) Water quality. In eastern Australia in the Murray-Darling River system, it is

predicted that the level of salinity will rise above the World Health Organisation’s

desirable limit for drinking (1000 mg/L total dissolved salts (TDS)) in Adelaide’s

water supply between 2050 and 2100 (National Land and Water Resources Audit

2001). Currently, in the south-west of Western Australia only 44% of total river

flow is fresh (< 500 mg/L TDS), with 10% marginal (500−1000 mg/L TDS), 21%

Recharge zone

Discharge zone

Recharge zone

Discharge zone

Native situation

Current situation

5

brackish (1000−3000 mg/L TDS), 20% moderately saline (3000−7000 mg/L TDS)

and the remainder has higher salinity levels (Mayer et al. 2004).

3) Biodiversity. By 2050, 130 important wetlands may become salinised (National

Land and Water Resources Audit 2001). In Western Australia, ecological

communities in the lower half of catchments will be lost (George et al. 1999a) and

450 animal and/or plant species and an unknown number of invertebrates, which

only occur in these environments, are at high risk of extinction (Keighery 2000).

4) Flood risk. It is predicted that flood flows will increase due to greater areas with

shallow water tables (George et al. 1999a). However, few studies have attempted

to quantify the impacts of increased flood risk.

In addition to the biophysical impacts of dryland salinity, social costs to rural

communities will be substantial; but these are harder to quantify (Pannell 2001). Despite

the already significant impacts of dryland salinity, considerable ethical and economic

incentives remain to implement strategies that can reduce the future consequences of

dryland salinity on the landscape of southern Australia.

Salinity management options

A range of options have been investigated for salinity management and show variable

capacity to increase water use and reduce recharge of groundwater tables on a large

scale. These include:

1) Engineering options, such as drains and groundwater pumps to remove excess water

from groundwater tables (mainly in discharge areas). These have been used with

some success, but their use is limited to certain soil types, their high cost is

prohibitive to wide-scale use and the disposal of the waste saline water is a major

problem (George and McFarlane 1993).

2) Increasing water use of winter growing annual crops and pastures in recharge areas

by improvements in agronomy. This approach is limited by the shallow root

systems of most annual plants and their inability to create a sufficient ‘buffer’ of dry

soil to significantly reduce the highly seasonal rates of drainage to the watertable

(Asseng et al. 2001). Deeper-rooted annuals that can dry the soil profile during

spring, such as Ornithopus spp. (serradella) (Nutt 1999), may be useful, but are

unable to utilise out-of-season (summer) rainfall.


3) Revegetation of the landscape with trees. Agroforestry will need to compete directly

on commercial terms with conventional crop and livestock production (Lefroy and

Stirzaker 1999). For example, in high rainfall areas (> 700 mm mean annual

rainfall) livestock enterprises have been replaced by Eucalyptus globulus Labill.

(Tasmanian blue gum) plantations (Pannell and Ewing 2004). However, plantation

forestry is currently unprofitable compared to other land uses in lower rainfall

environments (< 600 mm mean annual rainfall) (Pannell and Ewing 2004). Tree

productivity and water use can be enhanced by planting trees in water accumulating

sites or by alley plantings with crops (Lefroy and Stirzaker 1999). Although,

Stirzaker et al. (2002) conclude that mixing crops and trees becomes more difficult

with declining cropping season rainfall and increasing seasonal variability. In lower

rainfall environments there are few industries to support wide-scale agroforestry

ventures and new activities would need a long period of development and financial

support before they are commercially viable.

4) Replacement of annual pastures with deep-rooted perennial forages to reduce

recharge of groundwater tables. These forages would have the ability to remove

more water from the soil profile than shallow-rooted annuals, and would not require

the development of new industries (Cransberg and McFarlane 1994; Cocks 2001;

Dunin 2002; Ward et al. 2002; Ewing and Dolling 2003). This option represents the

most broadly applicable means to address dryland salinity. Perennial forages might

be used in discharge or recharge areas but the primary focus of this thesis is their

use in non-salt-affected areas to reduce recharge of groundwater tables.

The ability of perennial forages to slow or halt the spread of salinity will depend on

plant type, how plants are used and the scale of adoption. Variations between species in

plant form (e.g. tree, shrub or herb), growth pattern and extent of the root system will

greatly influence their effects on water use (Cransberg and McFarlane 1994). George et

al (1999b) suggest that between 50 and 80% of the landscape needs to be returned to

perennials to stop more land going saline. However, perennials may not be needed

permanently in all situations. For example, by incorporating perennial forages in

rotations or alleys, larger water use benefits are achieved relative to the proportion of

perennials in the landscape (Clarke et al. 1998). Nonetheless, the scale of change

needed will not occur based on salinity management benefits alone (Pannell and Ewing

2004). Perennials need to provide short term advantages to production and profit to

drive wide-scale changes from current systems.

7

Perennial forage options in a variable agricultural region

The challenge of finding profitable perennial forages that increase water use is further

complicated by the variability in climate, soil and production systems in the agricultural

regions of southern Australia. This variation means that a range of options are required.

This section will first describe the agro-climatic zones of southern Australia and then

use these to identify climatic regions where few perennial forage options currently exist.

Nested within these climate zones is a range of edaphic and management constraints,

which will also be discussed.

Agro-climatic zones

The regions of southern Australia where perennials are required span a range of agro-

climatic zones (Table 1 and Fig. 2). These are distinguished by mean monthly

temperature and precipitation (Hutchinson et al. 2005). These factors closely predict the

period and intensity of water deficit, not only annual periodic fluctuations but also

variability between years. Within these agro-climatic zones there is still substantial

variation in total rainfall and rainfall seasonality but for the purposes of this discussion

the characteristics of these climatic zones are generalised.

Although perennials were dominant in native vegetation across southern Australia

(Table 1), the suitability of the agro-climatic zones for productive perennials differs

significantly. For example, the temperate, cool season wet climate (Fig. 2) (D5) is the

most favourable, enabling perennials to persist and be productive. The annual rainfall in

this region is typically > 600 mm, with a relatively even distribution across the year.

Water deficit does occur during summer for short periods, but its severity is moderated

by cooler temperatures. In comparison, the dry Mediterranean environments (Fig. 2)

(E2) are particularly challenging for perennials. Average annual rainfall ranges between

300 mm and 500 mm, 85% of which occurs during winter and spring (May to October).

Summer rainfall is low and variable, while temperatures and evaporative demand are

high. Thus a long period of severe water deficit occurs each year during summer.

Perennial plants able to persist in this environment must possess adaptations to ensure

their survival such as larger root systems, minimisation of leaf area or osmotic

Table 1. Agro-climatic group, climate description, the current dominant land use and native vegetation structure of areas targeted for perennial plants in southern

Australia (adapted from Hutchinson et al. (2005) and Hobbs and McIntyre (2005)). Codes refer to Fig. 2 where distributions of these agro-climates are depicted.

Agro-climate Code Climate description Current dominant land use Native vegetation structure

Wet Mediterranean

climate

E1 Peaks of growth in winter and spring and

moderate growth in winter

Winter cropping, improved

pastures (sheep, cattle and

dairying), forestry and horticulture

Dominated by shrubland or open

woodland with shrubby understorey

Dry Mediterranean

climate

E2 Drier cooler winters and less growth than

E1

Winter cropping, improved

pastures (sheep) and horticulture

As above

Temperate,

subhumid

E3 Most plant growth in summer, although

summers are moisture limiting

Temperature limits growth in winter

Winter cereals and summer crops,

improved and native pastures

Open woodlands with grassy

understorey are widespread with

grasslands also common

Sub-tropical, sub-

humid

E4 Growth is limited by moisture rather than

temperature and the winters are mild

Growth is relatively even through the year

Winter cereals (after long fallows),

summer crops (including cotton)

and sown pastures

Open woodlands with grassy or shrubby

understorey are widespread, but

grasslands, shrublands and closed

forests are also common

Temperate, cool

season wet

D5 Moisture availability high in winter-spring,

moderate in summer, most plant growth in

spring

Forestry, cropping, improved and

native pastures and horticulture

Open woodlands with grassy or shrubby

understorey are widespread, with

shrublands also common

9

adjustment mechanisms (Monneveux and Belhassen 1996). However, these adaptations

come at a cost to productivity. Therein lays the inherent trade-off between yield and

persistence, and thus survival in more challenging environments will inevitably come at

a cost to productivity.

Figure 2. Distribution of the agro-climatic groups described in Table 1 (Hutchinson et al.

2005).

Although moisture supply is the main limitation in the other climatic zones, its intensity

occurs somewhere between the two extremes discussed above. Wetter Mediterranean

climates (Fig. 2) (E1) experience a longer growing season and cooler temperatures than

in drier regions, so the period and intensity of water stress during summer is lessened.

Compared to Mediterranean climates, the distribution of rainfall is more even

throughout the year in temperate, sub humid (Fig. 2) (E3) and subtropical, subhumid

climates (Fig. 2) (E4), thus potentially reducing the period of water deficit. However,

rainfall variability between years is larger than in Mediterranean climates and in dry

years, plant growth is significantly restricted.


Climatic constraints

The perennial forage options currently used extensively in southern Australia are

particularly skewed to high rainfall environments, where perennial plants can be

productive and conditions enable better survival. The most suitable agro-climatic

regions for the major perennial forages currently grown in southern Australia are listed

in Table 2. The majority of perennial grasses and legumes are best suited to moist

temperate regions (D5 in Fig. 2) where livestock grazing predominates as the major land

use. The obvious exception is lucerne (Medicago sativa L.), which is adapted to a broad

range of climates varying in annual rainfall from 300 to 1500 mm (Hill 1996). Based on

climatic constraints, Hill (1996) suggests that lucerne is potentially adapted to 96% of

the temperate agricultural zone in eastern Australia and 42% of south-west Western

Australia. However, lucerne distribution is actually limited by edaphic constraints

(discussed later). The shortage of alternative perennial legumes to lucerne for lower

rainfall regions has in some cases resulted in the use of perennial grasses, such as

phalaris (Phalaris aquatica L.), cocksfoot (Dactylis glomerata L.) and tall fescue

(Festuca arundinacea Schreb.), with mixed outcomes (Dear et al. 2003).

Resilience to drought is a vital characteristic for perennial species in regions with

seasonally wet/dry climates (E1, E2, E3 and E4 in Fig. 2). Perennials need not only to

survive seasonal stress cycles but also variations in annual rainfall. Among perennial

forages common adaptations to drought are, dormancy, the ability to reduce water use

by closure of stomata or leaf drop, and/or the development of deep roots that can access

water deep in the soil (Cocks 2003). Summer dormancy in varieties of phalaris,

cocksfoot and tall fescue has been shown to improve the persistence of these species in

lower rainfall environments (Reed 1996). Lucerne produces a deep root system,

enabling it to extend its growing season, but also reduces relative water content and

stomatal conductance in its leaves as plant water status declines (Sheaffer et al. 1988).

The leaves of lucerne will senesce under extreme conditions (Sheaffer et al. 1988) and

the plant will remain in a dormant state until water availability is restored. However, for

forage production, plants that maintain leaves under severe water deficit would be

particularly valuable.

Despite the relatively good adaptation of lucerne to periodic water stress compared to

other perennial forage species, its suitability for Mediterranean type climates with low

11

summer rainfall is poor (i.e. E2 in Table 1) (Cocks 2001). In these regions lucerne

survival relies on utilising historically stored water in the subsoil, and as stored moisture

declines so does plant density. In south-west Western Australia (E2 in Fig. 2), lucerne

densities typically decline by 13–40% over each successive summer, depending on

rainfall during this period (Dolling et al. 2005). Current lucerne cultivars have mainly

been selected for irrigated systems and improvements in adaptation of lucerne to more

arid dryland conditions may improve the sustainability of stand densities (Humphries

and Auricht 2001). Nonetheless, a greater variety of perennial forages that are able to

tolerate drought are needed to provide alternatives to lucerne in regions with

Mediterranean-type climates.

Edaphic constraints

In addition to the climatic factors already mentioned, the potential range of current

perennial forages is known to be limited by one or more of the following factors; soil

acidity, fertility and, primarily in groundwater discharge zones, salinity and

waterlogging (Table 2). Thus, within each agro-climatic zone species tolerant of these

stresses are required.

Soil acidity

Soil acidity is the major edaphic factor limiting the distribution of current perennial

forage options (Table 2). Estimates suggest that throughout southern Australia 33

million ha of land has a pHCa < 4.8 (Scott et al. 2000). The detrimental effects of low

soil pH are due to more than high concentrations of hydrogen ions, and also include

aluminium and manganese toxicity, reduced nutrient availability and reduced rhizobial

performance. Perennial pastures have a range of tolerances to these factors. For

example, cocksfoot and perennial ryegrass (Lolium perenne L.) are regarded as tolerant

of Al (i.e. 50% reduction in growth at > 10 µg Al/mL), while phalaris and lucerne are

considered sensitive and highly sensitive, respectively (i.e. 50% reduction in growth at

1.4–5 and < 1.4 µg Al/mL, respectively) (Scott et al. 2000). In legumes, the acid

tolerance of root nodule bacteria and their symbiotic association with the host legume is

a key limiting factor (Ewing and Robson 1990; Howieson and Ballard 2004). For

legumes, host plant tolerance of low pH and high Al needs to be coupled with an

association with acid tolerant Rhizobium.

Table 2. The suitable agro-climatic groups (codes from Table 1) and edaphic requirements for the current array of commercially available temperate perennial

forage species sown in southern Australia (based on recommendations of New South Wales Department of Primary Industries (New South Wales Department of

Primary Industries Agnote 2005) and analysis by Hill (1996)).

Pasture species Suitable agro-climatic groups Edaphic requirements

Herbaceous legumes

Lucerne (Medicago sativa L.)

D5 & E3 > E1 & E4 > E2 Best suited to deep, well drained fertile soils. Limited tolerance of waterlogging, soil acidity and soil aluminium (requires pHCa > 5.2 and soil Al < 5%).

White clover (Trifolium repens L.)

D5 Range of soils with medium to high fertility and good water-holding capacity in drier areas. Tolerant of soil acidity and aluminium (requires pHCa > 4.5 and soil Al < 20%).

Strawberry clover (Trifolium fragiferum L.)

D5 Tolerant of waterlogging and moderate salinity

Red clover (Trifolium pratense L.)

D5 Well-drained, fertile, slightly acid to neutral soils (requires pHCa > 5.2 and soil Al < 10%). Needs good moisture-holding capacity.

Caucasian clover (Trifolium ambiguum M. Bieb.)

D5 Grows on a wide range of soils but most successful on granitic neutral to acid soils with pHCa > 4.5.

Birdsfoot trefoil (Lotus corniculatus L.)

D5 > E3 Broad adaptation to diverse soil conditions. Tolerant of soil acidity (requires pHCa > 4.7) but not high levels of soil aluminium.

Greater lotus (Lotus pedunculatus Cav.)

D5 Tolerates waterlogging, low soil pHCa 4.5–5.5 and high levels of aluminium and manganese

Grasses/Herbs

Perennial ryegrass (Lolium perenne L.)

D5 Highly fertile soils, but will persist on lower-fertility soils as well.

Tall fescue (Festuca arundinacea Schreb.)

D5 > E3, for summer dormant types Moderate tolerance of soil acidity, high soil aluminium, salinity and waterlogging (requires pHCa > 4.8, soil Al < 15% and EC < 8 dS/m).

Phalaris (Phalaris aquatica L.)

D5 > E3 > E1 Best suited to high-fertility, deep, heavy-textured soils but will grow on a wide range of soils. Sensitive to soil acidity (requires pHCa > 4.2).

Cocksfoot (Dactylis glomerata L.)

D5 > E3, for summer dormant types Better adapted to well drained, acid and infertile soils than other grasses

Chicory (Chicorium intybus L.)

D5 > E3 Suited to free-draining, deep soils. Fertility levels need to be high for maximum production. Able to tolerate acid soils and high aluminium (requires pHCa > 4.2 and soil Al < 30%).

Shrubs

Tagasaste (Cytisus proliferus L.)

E1 Best suited to deep infertile sands

Saline tolerant

Tall wheat grass (Thinopyron ponticum Z. W. Liu & R. R. C. Wang)

n/a Tolerant of poorly drained soils and moderate salinity (< 20 dS/m)

Puccinellia (Puccinellia ciliata Bor)

n/a Greater tolerance of salinity (> 20 dS/m) and waterlogging than tall wheat grass

Saltbush (Atriplex spp.) n/a Saline sites where waterlogging is not severe


Breeding and selection in already established species is one method of overcoming the

current limitations of soil acidity. For example, crossing phalaris cultivars with Phalaris

arundinacea has produced hybrids which exhibit greater tolerance of acidic soils (Oram

et al. 1990). Alternative species may also play a role. Greater lotus (Lotus pedunculatus)

is more tolerant, and able to effectively nodulate at lower pH and higher Al levels than

other temperate forage legumes (Edmeades et al. 1991b;1991a; Wheeler and Dodd

1995). Other species within the Lotus, Trifolium and Dorycnium genera exhibit

tolerance of low pH and/or high Al levels, although their tolerance is less than greater

lotus (Schachtman and Kelman 1991; Wheeler and Dodd 1995).

The intolerance of current lucerne cultivars to soil acidity means that on acid soils in

lower rainfall regions no well adapted perennial forages are currently available. An

improvement in drought tolerance of acid tolerant grasses such as cocksfoot provides

one opportunity (Oram and Lodge 2003). Increasing Al tolerance and improving

rhizobial performance is a major objective of current lucerne breeding programs

(Humphries and Auricht 2001). Nonetheless, forage species with higher acidity

tolerance than lucerne would be extremely valuable in low rainfall environments of

southern Australia.

Soil fertility

The poor natural fertility of most Australian soils has resulted in significant benefits

from fertilizer applications for plant productivity of most exotic species (Handrek

1997). Declining terms of trade and increases in energy and fertiliser costs mean that the

profitability of fertiliser use could change (Ewing and Flugge 2004). Biologically fixed

nitrogen is likely to become increasingly valuable (Brennan and Evans 2001). The

fertility requirement of new species is an important consideration. Alternative perennial

forages tolerant of soil infertility might represent the best profit option on land with low

crop productivity. The Australian native flora are generally better adapted to low

nutrient availability than exotic species (Handrek 1997) and may be suited to low input

systems on soils of low fertility. Little research has explored their agricultural potential.

Waterlogging and salinity

Waterlogging stresses frequently occur in winter wet regions (mainly D5, E1 in Table

1), on soils with impeded sub-soil drainage and in groundwater discharge zones. Areas

prone to waterlogging have been estimated to be between 1 and 2 million ha in Western

15

Australia and 3.8 million ha in Victoria (Setter and Waters 2003). Lucerne is sensitive

to waterlogging (Humphries and Auricht 2001), while some perennial forages perform

well in waterlogged conditions e.g. strawberry clover (Trifolium fragiferum) and greater

lotus (Rogers et al. 2005). However, few species currently used can handle seasonal

waterlogging and subsequent drought conditions. Perennial grasses, such as tall wheat

grass (Thinopyron ponticum) and Rhodes grass (Chloris gayana Kunth.), have been

used with some success in waterlogged sites, where their summer activity assists in

drying the soil profile and provides green forage.

Tolerance of salinity is an obvious requirement of plants that might be used in discharge

zones. However, in most of these areas high salt concentrations are coupled with

waterlogging (Barrett-Lennard 2003a). The combination of these stresses compounds

the effects on plant growth (Barrett-Lennard 2003a). Highest levels of tolerance to both

these stresses are found in grasses and chenopod shrubs, which are substantially more

tolerant than the most tolerant legumes so far identified (Rogers et al. 2005). Perennial

species widely sown in salt-affected sites are puccinellia (Puccinellia ciliata), tall wheat

grass and saltbush (Atriplex spp.) (Table 2) (Barrett-Lennard 2003b). Of these species,

puccinellia has the greatest tolerance to salinity and waterlogging, while saltbush must

be sown in areas where waterlogging stresses are lower (Rogers et al. 2005). While

these species are well adapted to grow in saline and waterlogged sites, the productivity

of these pastures is poor.

Saltland pasture productivity would be greatly improved by nitrogen inputs from salt

and waterlogging tolerant legumes (Rogers et al. 2005). The annual legumes, balansa

clover (Trifolium michelianum Savi), persian clover (T. resupinatum L.) and burr medic

(Medicago polymorpha L.) are tolerant of short periods of waterlogging and mild

salinity (Rogers et al. 2005), which enables them to be grown on significant areas of

land. Of the perennial legumes currently used, strawberry clover is the most tolerant of

salinity and/or waterlogging (Rogers et al. 2005), but its distribution is limited to areas

with a year round water supply (D5 in Fig. 2 or water accumulating sites). A greater

array of species, particularly perennial legumes, are needed to improve the productivity

of pastures on salt-affected, seasonally waterlogged land and to improve water use and

reduce groundwater recharge in these areas.


Economic and management constraints

Despite the existence of suitable perennial forage species in many situations, the

perceived costs and uncertainty of success in establishment, coupled with poor

persistence under heavy or continuous grazing regimes and seasonal drought, are

constraints to adoption (Cransberg and McFarlane 1994). However, the establishment

cost of lucerne, which can be reliably established from commercially available seed, has

a minor impact on profitability because a small area is planted each year and costs are

spread over the length of the rotation (Kingwell et al. 2003). Presumably a similar

situation would exist with other perennial forage species, provided they can persist.

Nonetheless, many farmers have tried to minimise establishment costs by under-sowing

lucerne with crops to coincide lucerne establishment with the final year in a crop

sequence (Bee and Laslett 2002). When multiple years are required for establishment,

during which grazing must be excluded (e.g. shrubs), high establishment costs may

preclude system profitability. Adoptability of new perennial forages would be greatly

improved with suitable technologies to reduce establishment risk and cost.

More intensive grazing management is required for many perennial forage species than

is commonly practiced for annual pasture systems. For example, current lucerne

cultivars require a rotational grazing strategy with a rest period adequate to renew root

carbohydrate reserves (Lodge 1991). Similarly, in phalaris, periods of rest are required

to maintain production and persistence (Culvenor 2000; Lodge and Orchard 2000;

Virgona et al. 2000). A reluctance or inability to change from traditional set stocking

regimes to more intensive grazing systems will impact on the productivity and/or

longevity of these perennial forages. Improvements in the grazing tolerance of species

such as lucerne and phalaris are objectives of current breeding programs (Humphries

and Auricht 2001; Oram and Lodge 2003). The specific grazing management

requirements of new perennial forages will need to be investigated.

Other management restrictions to the adoption of some perennial forages include:

appropriate techniques and timing for removal (e.g. lucerne removal prior to a cropping

rotation) (Davies and Peoples 2003); and, the need for special management or

equipment (e.g. mechanical pruning of tagasaste (Cytisus proliferus)). In these cases,

practices to overcome these issues are now developed (Angus et al. 2000; Davies and

Peoples 2003), but similar issues will undoubtedly arise with new forage species.

17

Systems for perennial forages

The previous section highlighted the range of limitations to the current array of

perennial forages. This presents a number of opportunities where existing or new

species need to be developed to fill a niche. Overlain on top of the variation in soils and

climate within southern Australia are a range of ways perennial forages may be used in

agricultural systems. Perennial forages vary greatly in plant form, phenology, seasonal

activity and forage qualities. They can be described in four main categories based on

plant form; grasses, herbaceous legumes, other herbaceous dicotyledons, and shrubs.

The plant traits needed for systems that incorporate perennial forages will now be

discussed.

Monocultures vs mixed systems

Monocultures are likely to be most successful for perennial species in favourable

environments, where a higher density of perennials can be supported. Monocultures

simplify management by removing the need to manage a range of species within the

same space and/or time. However, in many situations mixtures with annuals or other

perennial species will be desirable. The benefits of legumes in mixtures for biological

nitrogen fixation and improving forage quality are widely recognised (Peoples and

Baldock 2001; Malhi et al. 2002). In lower rainfall areas only low densities of

perennials can be maintained and perennials may need to be integrated with annual

species to obtain adequate system productivity.

Permanent pastures

Livestock grazing on permanent pastures predominates in the wetter environments of

southern Australia (D5 and parts of E1 and E3 in Fig. 2). As previously discussed, the

majority of perennial forages are suited to these regions and have been developed for

these systems. In lower rainfall environments, cropping plays a larger role and

permanent pastures are unlikely to entirely replace cropping systems without a dramatic

change in the relative profitability of crop and livestock production (Ewing and Flugge

2004). In the crop/livestock regions, permanent pastures are useful in situations where

crops perform poorly such as salt-affected discharge sites and infertile soils or hilly

country in recharge zones.


Integration with crops

In regions where cropping is the dominant enterprise, perennial forages will need to be

integrated into cropping systems. These mixed systems need to be flexible enough to

respond to temporal changes in profitability between livestock and cropping enterprises.

This could occur by separating crops and pastures either temporally (e.g. phase farming)

or spatially (e.g. alleys) or by growing the two in a polyculture (intercropping).

Phase farming

Phase farming involves the separation of pastures and crops in rotations of a number of

years (Reeves and Ewing 1993). This system provides greater flexibility and

adaptability than traditional ley farming systems (Reeves 1987), which were based

loosely on 1:1 cycles of self-regenerating annual legume pastures and cereal cropping

(Puckridge and French 1983). The integration of a perennial species in the pasture phase

is, to quote Ridley et al. (2001, p 264), ‘one of the most promising innovations for

controlling recharge in cropping areas in Australia’. Deep-rooted perennial species

extract water from the sub-soil during the pasture phase, creating a dry soil ‘buffer’,

which is allowed to fill during cropping years to then be used again in the pasture phase

(Fig. 3). Ridley et al. (2001) calculated that under a perennial phase system with lucerne

in north-eastern Victoria (mean annual rainfall 600 mm) drainage to groundwater is

only likely to occur in 6% of years, compared to 55% of years under annual species.

Long-term modelling of drainage in south-western Australia suggests that a buffer of 70

mm would on average take 5 years to fill in a low rainfall environment (Merredin, 328

mm mean annual rainfall) and 2–3 years in a wetter environment (Moora, 462 mm mean

annual rainfall) (Ward et al. 2003).

Two key characteristics of lucerne contribute to increasing water use and reducing

groundwater recharge. First, lucerne is a summer active plant. All plants use water at the

rates similar to potential evapo-transpiration during winter and early spring (Ward et al.

2001). However, lucerne, by growing during spring and summer when atmospheric

evaporative demand is greater, can continue to remove water from the soil profile. The

ability of lucerne to respond quickly to utilise out of season rainfall during summer also

means that a dry soil profile is maintained (Ward et al. 2001). The second characteristic

of lucerne is its deep root system, that when accompanied with the previous trait enables

water to be extracted from deep in the soil profile (McCallum et al. 2001; Ridley et al.

2001; Ward et al. 2001). The size of the additional dry soil buffer typically ranges

19

between 50 and 100 mm (Table 3), and is primarily related to the depth of water

extraction from the soil. Thus, the buffer typically increases with the age of the stand

and is limited where poorly structured or acid subsoil impedes rooting depth (Dolling et

al. 2005).

Figure 3. Integrating herbaceous perennial forages in a phase farming rotation. During the

pasture phase water is extracted from the sub-soil, creating a dry soil ‘buffer’, which is allowed

to fill during cropping years to be then exploited again in the pasture phase; thus, drainage to the

watertable is minimised.

Notwithstanding the benefits of reduced drainage, lucerne has proven to be a successful

plant in phase farming systems for a number of other reasons. Despite the possible

negative effects on crop yield of drier soil conditions following lucerne (Hirth et al.

2001; McCallum et al. 2001), nitrogen fixed by lucerne improves crop yield and quality

for a number of years (Holford and Crocker 1997; Hirth et al. 2001). As a result of its

extended growing period, lucerne provides high quality feed earlier in autumn and for

longer into summer and responds to summer rainfall events to produce valuable forage

when annual pastures are not available. Thus, higher liveweight gains and higher

Wet soil

Dry soil

Year 1 – Establish pasture under cover crop

Year 2 – Pasture begins to create a dry soil buffer

Year 3 – Pasture creates large soil buffer

Year 4 – Pasture removal followed by crop

Year 5 – Continue crop rotation

Year 6 – Re-establish pasture under cover crop


stocking rates can be maintained on lucerne than pastures based on annual legumes

(Crawford and MacFarlane 1995) and there is a reduction in the cost of supplementary

feed during summer and autumn (Bathgate and Pannell 2002). Finally, as with

traditional legume-based pasture rotations, lucerne phases provide a disease break in

cereal-based cropping rotations (Reeves 1987) and enable effective weed control

without recourse to selective herbicides (Monjardino et al. 2004).

Table 3. Additional dry soil buffer created under lucerne in a number of studies in southern

Australia.

Additional buffer created Age of stand

(years)

Mean annual rainfall

Region Source

211 mm > annual pasture

101 mm > crop

1.5 525 mm Southern NSW

(Angus et al. 2001)

48 mm > crop 3–4 423 mm North-western Victoria

(McCallum et al. 2001)



2

3

525 mm Southern NSW



2

3

425 mm Southern NSW

(Sandral et al. in press)

206 mm > crop 5 year

mean

598 mm Northern Victoria

(Ridley et al. 2001)



2

2

387 mm

350 mm

South-western WA

(Latta et al. 2001)



2

2

370 mm South-western WA

(Latta et al. 2002)




1

2

3

483 mm South-western WA

(Ward et al. 2001)

In cropping cycles, perennial legumes have distinct advantages over non-legumes

because of the benefits of atmospheric nitrogen fixation for subsequent crops (Cocks

2001). Even when mixed with annual legumes, perennial grass-based swards fix less

nitrogen than pure subterranean clover or lucerne/clover mixtures (Dear et al. 1999).

The use of perennial grasses in rotation with crops would also reduce the capacity for

21

control of grass weeds and increase the risk of build-up of cereal crop diseases. Thus,

the suitability of perennial grasses for phase farming is questionable.

Lucerne satisfies many of the requirements of a successful plant for a phase farming

system. However, there are a number of limitations to its expansion. Humphries and

Auricht (2001) outline some breeding targets they believe will greatly improve lucerne

cultivars for phase-farming.

1) Improved grazing tolerance. This would reduce the need for rotational grazing.

2) Improved seedling vigour. This would improve the reliability and reduce the costs

of establishment and improve the competitiveness of seedlings with weeds or

cover crops.

3) Greater root depth. This would enable greater exploration of the sub-soil, creating

a larger dry soil buffer and reducing recharge. It would also improve drought

tolerance.

Lucerne provides a good model for other perennial forages that might be suitable in

phase-farming systems. Some generally desirable characteristics of perennial forages

are:

• Low cost and reliable establishment. Key factors are a cheap supply of seed, high

early vigour and competitiveness with weeds or crops, if under-sown with a crop,

and the capacity to be grazed in the establishment year.

• Ability to create a large dry soil buffer below the rooting depth of annual crops.

• Improvements in soil nitrogen fertility, for subsequent crops or non-legume pasture

components.

• Ability to provide high quality forage outside the growing season of annual

pastures.

• Opportunities to control crop weeds during the pasture phase. This might be

achieved either by using herbicides or by selective grazing of the associated weeds

when less palatable forages are used (Revell and Thomas 2004).

• Tolerance of low input grazing management.

• Easy removal at end of pasture phase.


Alley systems

Alley farming is a second existing system by which perennial forages might be

integrated into Australian farming systems. Alley systems enable other crop or pasture

species to be grown between spaced rows of trees or shrubs. The emphasis on

herbaceous forages in the past has meant that spatial segregation of forage plants has

rarely been needed. Woody forage species rarely outperform herbaceous perennial

forage plants for dry matter (DM) production or profitability due to allocations of

resources to inedible woody DM (Pannell and Ewing 2004). However, two forage shrub

species currently grown in alley systems in southern Australia, saltbush (Plate 1) and

tagasaste, utilise niches where herbaceous perennials are poorly adapted; saline

discharge sites and deep infertile sands, respectively (Lefroy 2001). Other shrubby

species may also be useful in areas where herbaceous perennials are unsuited and may

provide additional water use and profitability benefits.

Deep-rooted shrubs or trees when grown in alleys can achieve significant water use

benefits and reduce recharge of groundwater tables. Lefroy et al (2001) demonstrated

that alleys of tagasaste 30 m apart (20% of area) reduced drainage from 193 mm under a

monoculture crop to 32 mm. Tagasaste accessed approximately 70% of its water from a

fresh perched watertable at 5 m depth, utilising soil water during winter and depending

totally on groundwater during summer and early autumn (Lefroy et al. 2001). In

addition to the displacement of crop, alleys of trees or shrubs can compete with and

reduce yield of the accompanying crop. Consequently, there is a trade off between water

use benefits and reductions in grain yield. Stirzaker et al. (2002) have developed an

index which reflects the balance between the area of land protected from deep drainage

by trees (the no-drainage zone) and the area of land over which trees influence crop

yield (the no-yield zone). Where the no-drainage zone is larger than the no-yield zone

there are advantages for mixing trees and crops, but the opposite is the case when the

deficit to crop yield is greater than the drainage reduction benefits. Stirzaker et al.

(2002) and Lefroy et al.(2001), amongst others, emphasise the importance of uptake of

groundwater by trees in balancing environmental benefits and reductions in grain yield.

Maximum water use benefits are achieved where trees or shrubs can access usable

groundwater to directly draw down watertables.

23

Plate 1. Alleys of saltbush and volunteer annual pasture on a salt-affected discharge site in

south-west Western Australia. Photo courtesy of H.C. Norman.

Other considerations of alley systems with forage trees/shrubs include:

• The benefits from provision of shelter for reduced wind erosion (Sudmeyer and

Scott 2002) and protection of livestock (Gregory 1995).

• The opportunity to accumulate growth (i.e. long-lived leaves/stems) to be

exploited at times of critical shortage when other forage sources for livestock are

in short supply (Pannell and Ewing 2004).

• Technologies to reduce the cost and improve the reliability of establishment.

Although a one-off operation for long-lived shrubs or trees, planting of seedlings

can be very labour intensive and some woody species require a longer period of

establishment before grazing (Barrett-Lennard 2003b). Thus, establishment costs

can be large and in some cases prohibitive.

• Management to maintain the balance between woody components and fresh

growth of higher quality leaves and shoots. For example, if inappropriately

managed, tagasaste requires high cost mechanical pruning to encourage growth

located within the reach of livestock (Snook 1996). The strategic use of cattle

grazing as opposed to sheep reduces this need.


Intercropping

A polyculture consisting of a crop with one or more other species (intercropping or

companion cropping) is another system that might enable perennial forages to be

integrated into cropping enterprises in southern Australia. By growing a perennial

amongst an annual crop (Plate 2), excess water can be utilised during summer, while the

more profitable crop production continues during winter. This has not been widely

explored with perennial forage species. In one opportunistic study where all lucerne

plants were not removed prior to a cropping phase, Angus et al. (2000) found no

reduction in the yield of the accompanying wheat crop. However, protein content of the

grain was reduced, presumably due to competition for nitrogen during grain filling.

Angus et al. (2000) suggested that under drier seasonal conditions crop yield would be

reduced and proposed that intercropping would be most beneficial in wetter cropping

environments where competition for water during the crop growth period would be

lower. In wetter cropping environments a drier soil profile, created by the perennial

forage during summer, would also reduce or delay the effects of waterlogging stress on

following crops.

Plate 2. Intercropping trial with lucerne and wheat in south-west Western

Australia. Photo courtesy of Richard Bennett.

25

Required traits for perennials in intercropping situations include: low winter activity to

reduce competition for water and nutrients during the growing season of the annual

crop; nitrogen-fixation; prostrate habit to avoid contamination of crop products;

tolerance of chemicals commonly used in cropping systems; and ability to respond to

opportunistic rainfall events outside the crop growing season. Humphries and Auricht

(2001) suggest that lucerne varieties may be developed specifically for this purpose.

Other species may also possess the required traits.

Systems for alternative plant types

The three systems discussed in the previous section are used to varying degrees on

commercial farms in southern Australia and are fairly well understood. However, there

are a range of new plant types that may not fit neatly into these systems. In many cases

new species may require modified production systems to attain their full productive

potential.

While plants are described as being herbaceous, shrubby or tree, there is in fact a

continuum of forms (Fig. 4). Among the range of new forage species currently being

investigated, some semi-herbaceous plants with intermediate levels of ‘woodiness’ may

possess valuable characteristics to complement the current array of forage species.

Dorycnium spp., Bituminaria bituminosa (L.) C.H. Stirt. and some species of the genera

Astragalus, Coronilla and Lotus fall into this category (Woodgate et al. 1999; Dear et

al. 2003). The lack of knowledge about these semi-herbaceous species makes it difficult

to assess how they might be best utilised. They may be suitable as part of the sward in

permanent pastures, but in cropping areas a suitable system is less obvious. Semi-

permanent pastures in long rotation with crops may be an alternative system for such

plants.

Figure 4. Variation in plant form between selected forage species on a continuum between

herbaceous and woody trees.

Grasses, Trifolium spp.

Semi-herbaceous Shrubs Trees

Lucerne Tagasaste Eucalyptus

trees Saltbush

Herbaceous

Dorycnium


In addition to semi-herbaceous plants, other plant types which may be used for multiple

purposes include:

• Herbaceous perennial species that can be utilised for grain and forage. For

example, Microlaena stipoides (Labill.) R.Br. (weeping rice grass), a native

perennial grass, possesses large seeds that may be suitable for grain production

(Davies et al. 2005), but could also be utilised for forage. Perennial wheat, if

sufficiently high-yielding, could also open up opportunities for development

(Scheinost et al. 2001).

• Multi-purpose shrubs grown for forage but also other products (e.g. timber, other

wood products, biomass or oils) (Bartle 1999). These species could be grown as

permanent block plantings on land with low productivity or in long-term rotations

with crops. However, establishment and removal costs for woody species may be

prohibitive to the later option and industries would require development.

Livestock production considerations

In addition to adaptation to climatic and edaphic conditions, and systems requirements

for new perennial forages, their value for livestock is also an important consideration.

Livestock production is the main driver of profit from pasture systems and benefits of

forage species to animal performance and/or carrying capacity will be key factors

influencing their adoption. Forage nutritive value, palatability, the presence of anti-

nutritional factors and the timing of feed availability are all important.

Nutritive value of forage refers to nutrient digestibility and efficiency of utilisation per

unit of feed intake. However, animal performance is also greatly dependent on forage

selection and voluntary feed intake. Sufficient forage, which is easy to collect, is an

obvious requirement to maximise feed intake, while forage digestibility and voluntary

feed intake have been shown to be positively correlated (Baker and Dynes 1999). In

addition, low palatability, poor adequacy of essential nutrients, high resistance to

mastication or rumination, or high contents of water, electrolytes or deleterious

secondary compounds can limit intake (Baker and Dynes 1999).

27

Despite the obvious advantages of highly productive and digestible forages, timing of

feed availability is also important. The seasonal pattern of plant growth in southern

Australia means that animal numbers are limited by feed availability at the time of

minimum feed supply, unless high cost supplementation is undertaken. Perennial

forages provide an opportunity to fill this ‘gap’ in the supply of forage from annual

plants. For example, the economic value of lucerne in Mediterranean climates has been

closely related to provision of high quality feed during summer and autumn (Bathgate

and Pannell 2002). Species with lower forage quality may also play an important role to

fill this gap. Plants that can accumulate and maintain forage when other forage sources

are in short supply will greatly reduce the cost of supplementary feeding. Saltbush on

saline discharge sites is an example of a successful system based on this principle

(Barrett-Lennard 2003b). Thus, forages with lower palatability and feeding value may

be advantageous to allow forage to accumulate when other feed sources are available

and to moderate animal intake when feed is short.

Forage plants often contain anti-nutritional factors which have evolved as an herbivory

defence. Secondary plant compounds, in particular, can have detrimental impacts on

animal performance and health (e.g. toxins, tannins). Grasses, which are

morphologically and physiologically well adapted to grazing by herbivores, generally

have few toxins, while a wide range of toxic compounds are found in legumes. Some

toxins present in perennial forages include: cyanogens in some Lotus spp. (Gebrehiwot

and Beuselinck 2001); isoflavones with oestrogenic effects in Trifolium spp.;

coumestans in Medicago spp. (Waghorn et al. 2002) and toxins of microbial origin in

some grasses such as perennial ryegrass and phalaris (Culvenor 1987). In undeveloped

forage species, breeding to remove or reduce toxins may be needed prior to further

development.

Condensed tannins (CT) are secondary plant compounds found commonly in legumes

and browse species, but also in some other dicotyledonous plants. A range of alternative

perennial legumes possess condensed tannins, including L. corniculatus, L.

pedunculatus, Hedysarum coronarium L., Onobrychis viciifolia Scop. and Dorycnium

spp. (Waghorn et al. 1998). Depending on their concentration in the feed consumed by

livestock, CT can have beneficial or detrimental effects on forage value. Condensed

tannins bind to plant proteins and reduce their degradation by bacteria in the rumen


(Waghorn and Molan 2001). When in low concentrations (20–45 g CT/kg DM) CT can

increase amino acid absorption in the small intestine, which can increase milk

production, wool growth, ovulation rate and lambing percentage (Min et al. 2003).

Other animal health benefits of reduced bloat risk and reducing internal parasite burdens

have also been attributed to forage containing CT (Min et al. 2003). Therefore the

benefits of forages containing CT to animal production and health might be explored.

However, high concentrations of CT (> 55 g CT/kg DM) reduce forage digestibility and

voluntary feed intake (Min et al. 2003).

Conclusion

Deep-rooted perennial forages provide an opportunity to address dryland salinity and

improve the sustainability of agriculture in southern Australia. The majority of perennial

forages currently available are best suited to higher rainfall environments where

livestock grazing is the predominant enterprise. In lower rainfall regions, lucerne is the

bench mark and an expansion of its role can be achieved with improvements in

tolerance to soil acidity and waterlogging. Nevertheless, a range of new species are

needed to provide diversity, to reduce widespread disease risk and to fill niches where

lucerne is not well adapted. Drought tolerant species for dry Mediterranean climates and

tolerance to soil acidity, infertility, salinity and waterlogging are all characteristics of

forages that would prove useful. The capacity to increase water use must also be

assessed for each species to estimate the reduction in recharge that can be achieved.

The challenge exists to not only provide perennial forages that increase water use but

also ensure these provide profitable alternatives to traditional agricultural systems. In

most cases, perennial forages will need to be integrated with annual crops or pastures.

Phase farming, alley cropping and intercropping all provide systems by which excess

water from annuals can be utilised by perennial plants to produce forage for livestock.

Plant form and function will greatly influence the best system for a particular species.

However, to be integrated successfully in these systems, appropriate agronomic traits

need to be considered and these are summarised in Table 4. In some cases, new species

with a specific benefit may require modified production systems for their full potential

to be exploited; a good understanding of their agronomic strengths and limitations

would be required to design appropriate systems.

29

Table 4. Suitable plant form and function and desirable agronomic characteristics for perennial

forages in a range of agricultural systems

System Suitable plant form and function

Desirable agronomic characteristics

Permanent pastures Herbaceous grasses and forbs

Adapted to non-cropping land e.g. saline, infertile

Persistent under grazing

Long-lived or regenerate reliably

Incorporates legumes (either annual or perennial)

Short-term rotations (i.e. 2–4 years) e.g. phase farming

Herbaceous legumes Deep-rooted and possess an ability to establish a large dry soil ‘buffer’

Summer activity and responsive to out of season rain

Low risk and cost of establishment

• Good early vigour and competitive with weeds

• Cheap source of seed

• Able to be grazed in first year

Ability to control weeds during pasture phase

Tolerance to minimal grazing management

Long-term rotations (i.e. > 4 years)

Herbaceous to semi-herbaceous legumes or grasses (if combined with legume)

Multi-purpose shrubs

Long-lived and tolerant of grazing

Deep-rooted to create a buffer sufficient to capture drainage from crop for many years

Provide multiple benefits e.g. drought forage, timber production, animal health benefits

Easy establishment and removal

Alley systems Woody species (mostly shrubs)

Provide forage out of season

Root morphology or growth cycle that minimises competition with crops

Moderate palatability

Maintain reasonable nutritive value year round

Low management requirement

Intercropping Prostrate, leguminous

Winter dormancy to reduce competition with crop

Prostrate habit to reduce crop product contamination

Responsive to out of season rain

Tolerance to in-crop herbicides

Non-carrier of crop diseases and pests


Research objectives

This chapter outlined climatic, edaphic and management constraints to current perennial

forage options. The objective of the research presented in this thesis is to investigate the

suitability of Dorycnium as a forage plant for dryland salinity management in recharge

zones. The species in Dorycnium are sub-shrubs or semi-herbaceous and have been

subjected to little or no past domestication or breeding. Little is known about the

agronomy of these plants. Thus, their potential water use benefits and key agronomic

traits that might affect how they are integrated into systems need to be assessed. Two

species in particular, Dorycnium hirsutum and D. rectum have performed well in

preliminary experiments in south-western Australia. Although other Dorycnium species

are discussed, the focus of the experimental work is on D. hirsutum and D. rectum

The thesis will first review the current state of knowledge on using Dorycnium as a

forage plant (Chapter 2). Then using eco-geographical techniques some ecological

factors affecting the distribution of Dorycnium species in their native environment are

explored and predictions made on their suitability to the environments of southern

Australia (Chapter 3). Chapter 4 will compare the water use of Dorycnium to lucerne

and annual pastures to determine its potential value for reducing recharge of

groundwater. A number of factors relating to the establishment and drought tolerance of

Dorycnium seedlings are investigated in Chapters 5, 6 and 7. In Chapter 8 the influence

of grazing management, simulated by cutting, on production and nutritive value of D.

hirsutum and D. rectum is examined. Overall, these investigations will identify the

strengths and limitations of Dorycnium species and provide information on some key

agronomic factors that will influence the agricultural systems in which they may fit.

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31

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Chapter 2: The potential of Dorycnium as a forage plant to

manage water in the landscape: a review of its agronomic

characteristics

Abstract

The genus Dorycnium contains species that might aid in the management of dryland

salinity in agricultural systems of southern Australia. However, Dorycnium species are

not currently used commercially and little is known about the agronomic characteristics

of the genus. This review covers the current knowledge on Dorycnium distribution and

taxonomy and agronomic issues, such as adaptation, establishment, biomass production,

grazing management and nitrogen fixation and considerations for animal production.

Some Dorycnium species originate from regions of the Mediterranean that have

provided many pasture species to southern Australia in the past. Little data exists on the

climatic and edaphic conditions to which Dorycnium spp. are best adapted. Current

evidence suggests that Dorycnium have potential for acid soils and might be suitable for

the drier climates of agricultural regions. However, the capacity of Dorycnium to

increase water use and where and how these plants might be best used in agricultural

systems of southern Australia is yet to be determined.

Currently Dorycnium species appear to have significant limitations in establishment

reliability and forage quality. However, breeding may be able to overcome or minimise

these limitations. Establishment techniques might also be improved. High levels of

condensed tannins appear to be related to low forage digestibility in Dorycnium.

However, appropriate dietary levels of condensed tannins can positively affect animal

performance and health. Despite the apparent poor forage quality of Dorycnium, these

plants may have a role to provide feed when other forage sources are in limited supply.

A great deal more information is required to more fully determine the potential of

Dorycnium in southern Australia.

Chapter 2: Review of agronomic characteristics of Dorycnium 40

Introduction

A range of new perennial forage plants are currently under investigation in southern

Australia. New perennial pasture species that can be incorporated into current annual-

based agricultural systems to reduce groundwater recharge and slow the spread of

dryland salinity are needed. Lucerne (Medicago sativa L.) is currently the most widely

used perennial pasture in agricultural regions of southern Australia. However, a variety

of species are needed to fill niches where few options currently exist (i.e. waterlogged

and/or saline soils, acid soils and regions with low summer rainfall) and to provide

diversity to reduce the ecological risk of relying primarily on one species. Species under

consideration include exotic temperate grasses and legumes, subtropical grasses and

native plants (Cocks 2001; Bennett et al. 2003). These species range from ones that

have been actively selected and are widely used for agriculture, to species that are in the

process of being domesticated. The canary clovers (Dorycnium spp.) have performed

well compared to other perennial legumes tested in trials in Western Australia (G.A

Moore, unpublished data). Thus they have been identified as potential forage legumes

that may provide an alternative to lucerne and play a role in the management of dryland

salinity (Bennett 2002; Bennett et al. 2003; Dear et al. 2003). However, Dorycnium has

only recently been domesticated and little is known about its agronomic characteristics.

Information on Dorycnium originates from three main sources. First, D. hirsutum (L.)

Ser. and D. pentaphyllum Scop. are used as ornamental species because of their

distinctive foliage and copious flowers (Reid 1995). However, knowledge generated

from this application has little agronomic significance. Secondly, Dorycnium species are

documented in studies of native vegetation communities in the Mediterranean basin,

their native distribution. In particular the presence of D. pentaphyllum and D. hirsutum

has been described in rangeland pastures (Viano et al. 1995; Barroso et al. 2001).

Thirdly, the majority of literature and knowledge of Dorycnium in relation to agriculture

originates from New Zealand, where Dorycnium has been trialled with some success for

soil conservation and forage uses. Although similar research has been conducted in

Australia, mainly Tasmania, most of it is unpublished. This chapter will summarise the

current literature and knowledge of species within the genus Dorycnium, with a

particular view to agricultural production and dryland salinity amelioration. Strengths

41

and weaknesses of Dorycnium will be highlighted and areas requiring further

investigation identified.

Taxonomy and distribution

In the past the species in Dorycnium were included in Lotus L. (Ball 1968). Dorycnium

is still included in the Loteae tribe and is closely related to Lotus (Arambarri 2000). The

taxonomy of Dorycnium is complicated, but 6 species are described from the ‘Flora

Europaea’ (Ball 1968) and the ‘Flora of Turkey and the East Aegean Islands’ (Demiriz

1970) (Table 1). Three of these species, D. hirsutum, D. rectum and D. pentaphyllum,

are widely distributed across the Mediterranean region of Europe, North Africa and

west Asia, while the other three species have smaller distributions. Despite the wide

distribution of D. rectum, it is rare and mainly located in moist areas or close to sources

of water (Woodgate et al. 1999). A large number of subspecies of D. pentaphyllum are

documented in the literature, many of which are considered as separate species by some

authors. However, in many cases, these taxa are synonymous with the 6 main

subspecies of D. pentaphyllum (Table 1). The taxa of D. pentaphyllum seem to have

distinct distributions in Europe and the Mediterranean. Intermediate types are

documented in areas of overlap (Tasenkevich 1994; Slavik 1995). Three other species

not listed in Table 1 have been described in Dorycnium by Greuter et al. (1989); D.

sanguineum Vural, D. fulgarans (Porta) Lassen, which is synonymous with D.

pentaphyllum ssp. fulgarans (Porta) Cardona, and D. strictum (Fischer and Meyer)

Lassen, which is also known as Lotus albus Janka or L. strictus Fischer and Meyer.

Dorycnium species, other than D. rectum, are usually found in areas with low soil

fertility, especially on sandy soils (Allen and Allen 1981). Typical habitats include

rocky ground, steppes, macchia, deciduous woodland, coniferous woodland, fallow,

meadow or pasture and seashores (Woodgate et al. 1999). Little other information is

documented on the climatic and edaphic conditions or the vegetation communities in

which Dorycnium species occur.

Table 1. Dorycnium taxa (common names in parentheses), synonyms and countries of origin. Summarised from GRIN (2002), ILDIS (2004), Flora Europaea (Ball 1968) and Flora of Turkey and the East Aegean Islands (Demiriz 1970).

Species Subspecies Synonyms Countries of Origin

D. hirsutum (L.) Ser. (Hairy Canary Clover)

Lotus hirsuta L.; Bonjeania hirsuta (L.) Reichb.; B. syriaca Boiss.; Dorycnium hirsutum (L.) Ser. var. syriancum (Boiss.) Boiss.

Africa: Algeria, Libya; Asia: Israel, Lebanon, Syria, Turkey; Europe: Albania, France (incl. Corsica), Greece (incl. Crete), Italy (incl. Sardinia, Sicily), Portugal, Spain, Yugoslavia

D. rectum (L.) Ser. (Unciana)

Lotus recta L.; Bonjeania recta (L.) Reichb. Africa: Algeria, Libya, Morocco, Tunisia; Asia: Cyprus, Israel, Lebanon, Syria, Turkey; Europe: Albania, France (incl. Corsica), Greece (incl. Crete), Italy (incl. Sardinia, Sicily), Portugal, Spain

D. graecum (L.) Ser. Lotus graecus L.; D. latifolium Willd.; D. kotschyi (Boiss. and Reut.) Boiss.; D. latifolium Willd. var. kotschyi (Boiss.) Rikli.

Eastern part of Balkan peninsula; Bulgaria, Greece, USSR (Crimea), Turkey

subsp. pentaphyllum D. suffruticosum Vill.; Lotus dorycnium L. Algeria, Tunisia, France, Italy, Portugal, Spain (incl. Beleares)

subsp. germanicum (Gremli) Gams

D. germanicum (Gremli) Rikli.; D. sericeum (Neilr.) Borbas; D. jordanii var. germanicum Gremli

Central Europe and Balkan peninsula

subsp. gracile (Jordan) Ruoy

D. gracile Jordan ; D. herbaceum ssp. gracile (Jordan) Nyman; D. jordanii Loret and Barr.; D. herbaceum ssp. jordanianum Quezel and Santa; D. jordanianum Willk.

Mediterranean coasts of France and Spain

subsp. herbaceum (Vill.) Rouy

D. herbaceum Vill.; D. intermedium Ledeb. Algeria, Central and south-eastern Europe, Ukraine-Crimea Armenia, Azerbaijan, Georgia, Russia, Dagestan, Krasnoyarsk, Turkey

subsp. anatolicum (Boiss. and Heldr.) Gams

D. anatolicum Boiss. and Heldr.; D. libanoticum Boiss.; D. haussknechtii Boiss. var. libanoticum (Boiss.) Boiss.

Turkey, Lebanon (possibly)

D. pentaphyllum Scop. (Prostrate Dorycnium, Scarrillo)

subsp. haussknechtii (Boiss.) Gams

D. haussnechtii Boiss.; D. reesei Hub.-Mor. Endemic to Iraq – Turkey element

D. amani Zohary Endemic to Turkey

D. axilliflorum Hub.-Mor.

Endemic eastern Mediterranean element

43

Description of Dorycnium species (adapted from Demiriz (1970))

Dorycnium contains species that range in growth form from perennial herbs to shrubs

and are often referred to as ‘sub-shrubs’. D. hirsutum is a perennial herb or small shrub

with stems growing to a length of 20–50 cm (Plate 1a). The leaves, stems and flowers,

as the name suggests, are covered in hairs (Plate 1b). Leaflets sit close to the stem, with

a very short or absent rachis. They are grey-green and consist of 5 leaflets

(approximately 7–25 × 3–8 mm) the lowest pair simulating stipules. Flowering occurs

in mid-summer with a head of 4 to 10 white or pink flowers (9–15 mm in length) on the

inflorescence. Seed pods are 6–12 mm long, contain 2–6 seeds and do not contort at

maturity (Plate 1b).

D. rectum has a more erect habit than D. hirsutum and grows to a height of 150 cm

(Plate 1c). Leaflets are attached to stems on a distinct rachis with a length of 5–10 mm

(Plate 1d). The inflorescence consists of 20 to 40 white or pink flowers in a head.

Flowers are typically smaller than in D. hirsutum (4–7 mm in length). The seed pod is

10–20 mm long, contains 5–8 seeds and contorts at maturity.

D. graecum grows to 20–90 cm high. The rachis of leaflets is absent or very short.

Flowering heads possess 10 to 25 white flowers, again smaller than D. hirsutum (5–8

mm).

D. pentaphyllum possesses a more prostrate habit than the other Dorycnium species,

with stems growing to a length of 10–80 cm (Plate 1e). Leaflets do not possess a rachis,

with leaflets varying in shape from linear to obovate-oblong (Plate 1f). D.

pentaphyllum, D. amani and D. axilliflorum differ from the 3 species described above

because the flower calyx-teeth are unequal in size and each seed pod contains only 1

seed. Some uncertainty exists about the separation of D. amani, as its distribution is

similar to D. pentaphyllum ssp. haussknechtii and as such they may be synonymous.

However, it is described with a different leaf shape and size from the latter taxon

(Demiriz 1970). D. axilliflorum is only described from a few collections and is

differentiated from other Dorycnium species by the 2 to 3 subsessile (or short peduncle

(1–3 mm)) flowering heads that grow from the leaf axils.


a b

c

f e

d

Plate 1. D. hirsutum plant habit (a), flower and seed pods (b); D. rectum plant

habit (c) and foliage (d); and D. pentaphyllum plant habit (e) and flowers (f).

45

Plant improvement

Dorycnium species have been subjected to little or no domestication, with no registered

varieties. They are utilised in their native distribution for honey production (Petkov

1977; Perez Arquillue and Gomez Ferreras 1986; Sala Llinares 1989) and as a forage in

rangeland grazing systems (Viano et al. 1995; Barroso et al. 2001). D. pentaphyllum

ssp. herbaceum was also successfully trialled to stabilise areas prone to landslides in

northern Italy (Francescato and Scotton 1999). However, Dorycnium are not sown as

pastures and there is no record of their development for agricultural production in

Europe.

The potential of Dorycnium spp. was first documented by Crampton (1946) who

identified that D. hirsutum had potential as a forage plant and for soil erosion control in

California. Similarly, Brockwell and Neal-Smith (1966) suggested that D. hirsutum may

have some useful qualities for Australian pasture systems. In New Zealand, D. hirsutum

and D. pentaphyllum have been trialled with some success for revegetation and as a

forage in drought-prone and semi-arid areas in the South Island (Wills 1983; Sheppard

and Douglas 1986; Woodman et al. 1992; Wills et al. 2004) and on light-textured soils

in the North Island (Douglas and Foote 1994; Douglas et al. 1996b). D. hirsutum and D.

pentaphyllum also provide year round vegetative groundcover and prevent soil erosion

(Wills 1984; Sheppard and Douglas 1986; Wills et al. 2004). Dorycnium rectum has

been trialled in New Zealand, but its success was variable (Douglas et al. 1996a). A

plant improvement program incorporating Dorycnium species has been established in

New Zealand (Douglas 1993). However, no commercial cultivars have been released. In

Tasmania, Dorycnium has been trialled as an alternative forage to improve productivity

in areas where current pasture species are not well suited (Lane et al. 2004). Selection

work on D. hirsutum is underway in Tasmania and a commercial release of a cultivar is

expected in the next 3–4 years (Eric Hall, pers. comm.).

Agronomic factors affecting the potential of Dorycnium

Lucerne, because of its deeper roots and longer growing season, uses more water than

annual crops and pastures and thus reduces groundwater recharge and the development

of dryland salinity (Ridley et al. 2001; Ward et al. 2003; Dolling et al. 2005). No

previous water use studies have included Dorycnium and its value for salinity

management needs to be assessed. Much of the information available on Dorycnium in


agricultural systems originates from New Zealand, where performance appears site

specific, with variability in results between sites largely unexplained. In addition, no

general recommendations are currently available about the best management of

Dorycnium species or the conditions to which they are best adapted.

The key agronomic issues of adaptation, biomass production, establishment, grazing

management and nitrogen fixation will now be addressed. The majority of previous

work has focussed on D. hirsutum, D. rectum and D. pentaphyllum, thus these species

will be the focus of this review.

Adaptation

Dorycnium can tolerate harsh climatic conditions in a range of edaphic environments. In

New Zealand, D. hirsutum and D. pentaphyllum perform well in semi-arid and drought

prone areas where they also seem to tolerate frost (Wills 1983; Sheppard and Douglas

1986; Douglas et al. 1996b). Thus, performance is also good where rainfall is 300–600

mm, evapo-transpiration is high (> 1200 mm p.a.), on exposed, windy sites (up to 250

km per day), and where winter temperatures are low (-12ºC) (Sheppard and Douglas

1984). Information on the adaptation of D. rectum to challenging environments is very

limited. Overall, the suitability of the climatic regions of southern Australia for

Dorycnium species is unknown.

The edaphic requirements of Dorycnium are not well understood, though it appears to

be able to grow in a wide variety of soils. In New Zealand, Sheppard and Douglas

(1984) describe Dorycnium species as best adapted to free-draining soils that are prone

to water stress, while growth was poor on wet soils or soils with a high clay content,

where plants were frequently killed by root rot during winter (Sheppard and Douglas

1986). Dorycnium also appears tolerant of low to moderate fertility (Wills 1984;

Douglas and Foote 1994), but benefits from the application of fertiliser, particularly

phosphate (Wills 1983).

Much of the southern Australia possesses acid soils (pH CaCl2 < 5.0). This is a major

limitation to most current lucerne cultivars and species better adapted to acid soils are

needed (Chapter 1). Sheppard and Douglas (1984) suggest that Dorycnium is adapted to

weakly acid to alkaline soils with a soil pH from 5.2 to 8.5. However, it is unclear how

soil pH was measured in this study. Wheeler and Dodd (1995) measured the tolerance

47

of Dorycnium species to aluminium toxicity (commonly associated with acid soils) in a

multi-species study. The aluminium activity that reduced yields by 50% (AlRY50) in D.

hirsutum accessions ranged from 0.84 to 1.51 µM in shoots and from 1.44 to 2.53 µM in

roots (Wheeler and Dodd 1995). One accession of D. pentaphyllum showed a similar Al

tolerance level (AlRY50 1.24 µM in shoot and 1.4 µM in roots) (Wheeler and Dodd

1995). The tolerance of Dorycnium to aluminium was greater than all accessions tested

from the genera Melilotus and Medicago (Wheeler and Dodd 1995). No direct

comparisons of Al tolerance between Dorycnium and lucerne have been made.

However, Wheeler and Dodd (1995) found some D. hirsutum accessions were more

tolerant of Al than commercial Lotus corniculatus cultivars, which are more tolerant of

high aluminium and low pH than lucerne (Edmeades et al. 1991b;1991a; Schachtman

and Kelman 1991). Further investigation of the tolerance of Dorycnium to low pH and

high aluminium is required, but based on current evidence it seems tolerance of acid

soils is superior to lucerne.

Establishment

Little is known about the germination and emergence characteristics of Dorycnium seed.

Of the three most studied species, D. hirsutum has larger seeds (4.4 mg) compared with

D. pentaphyllum (2.7 mg) and D. rectum (1.4 mg) (Douglas and Foote 1994). Plants

with larger seed size generally produce seedlings of greater biomass (Cooper 1977) and

tend to be found in environments where shading or drought stresses are more common

(Baker 1972). Emergence and survival of Dorycnium in New Zealand trials was

variable and appeared greatly affected by environmental conditions and the time and

method of sowing. The percentage of seed sown that emerged was also lower than for

lucerne; 11% for D. hirsutum, 31% for D. pentaphyllum and 36% for D. rectum,

compared to 64% in lucerne (Douglas and Foote 1994). Slower germination and

emergence than lucerne may contribute to these differences. Douglas and Foote (1994)

recorded the days to initial emergence of scarified seed of D. hirsutum, D. pentaphyllum

and D. rectum to be 13.7, 11.3 and 11.3, respectively, which was slower than all other

perennial legumes tested. The duration of emergence was also longer and the time to

final emergence, > 22 days after sowing in all Dorycnium species, compared to 12 days

for lucerne. Douglas et al. (1996b) found that moving sowing from autumn to spring

improved emergence of D. hirsutum from 8 to 25% and D. pentaphyllum from 12 to

27%. The emergence of D. hirsutum has also been improved by 50% when sown with a

strip-seeder compared to a hoe coulter due to greater seedling protection and reductions


in competition from weeds (Wills and Trainor 2000; Wills et al. 2004). Thus,

improvements in the strategies of establishment are possible.

In response to the slow establishment and poor seedling vigour of Dorycnium, a period

of 2 seasons of growth before grazing is commenced has been recommended (Wills

1983; Sheppard and Douglas 1984). Despite some limitations in the ability of

Dorycnium to establish, complete failure has not been documented in trials in New

Zealand. In a number of trials, D. hirsutum and D. pentaphyllum established

successfully under drought conditions (Douglas and Foote 1994; Wills and Trainor

2000) and more effectively than lucerne, Lotus corniculatus and Lotus tenuis (Douglas

et al. 1996b).

Establishment costs and risk currently limit the adoption of perennial pastures in

southern Australia (Cransberg and McFarlane 1994). Poor early vigour, and as a

consequence the 2 growing seasons required before grazing, will be a major limitation

for integration of Dorycnium into farming systems in southern Australia. Increased

knowledge of germination requirements, better seeding technology, selection for

improved seedling vigour and development of techniques that reduce cost (e.g. under-

sowing with crops) and improve reliability of establishment are needed.

Biomass production

Biomass production of Dorycnium has mainly been measured in New Zealand, where

Dorycnium can be very productive and produce valuable amounts of biomass. D. rectum

produced 3.8 t DM/ha in its first year and > 20 t DM/ha in its second year (Table 2)

(Douglas and Foote 1994). However, at a nearby site D. rectum productivity was much

lower; 0.2 t/ha in the first year (Douglas et al. 1996a). Douglas and Foote (1994) found

D. hirsutum to produce more DM than lucerne in its first year, although production from

lucerne in year 2 was much higher (Table 2). Wills et al. (1989a) documented

production of D. hirsutum of approximately 1.4, 9.8 and 7.4 t DM/ha in the first, second

and third years, respectively, after sowing. In this trial, D. hirsutum out-yielded lucerne,

which produced 1.0, 6.7 and 7.7 t DM/ha over the first three years of production (Wills

et al. 1989a). Experience in Australia and current evidence suggests that first year

biomass production from D. pentaphyllum is lower than D. hirsutum and lucerne. In

New Zealand, Douglas and Foote (1994) measured DM production of < 0.5 t DM/ha

from D. pentaphyllum in its first year; a fraction of lucerne or D. hirsutum (Table 2).

49

However, D. pentaphyllum is far more productive in subsequent years. Overall, it

appears that productivity of Dorycnium species is site specific with some critical

limiting factors not yet known, but in some cases Dorycnium species can be as

productive as currently cultivated perennial forage legumes.

Table 2. Dry matter production and the proportion of biomass that consisted of leaf for

Dorycnium spp. and lucerne during the first two years after sowing at Palmerston North, New

Zealand (Douglas and Foote 1994). Grazing was excluded from this trial.

Accumulated shoot biomass

(t DM/ha) Leaf (%)

Species

Year 1 Year 2 Year 1 Year 2

D. hirsutum 3.7 5.6 66 54

D. pentaphyllum 0.3 10.2 88 38

D. rectum 3.8 20.6 44 34

Lucerne 1.0 14.4 – 36

In New Zealand, seasonal biomass measurements of D. hirsutum show that DM

production peaks in late spring but herbage is produced throughout the year (Wills et al.

1989a). Wanjiku et al. (1997) also found that there was little effect of season on DM

production of D. hirsutum; 6.8 t/ha harvested in spring (November), 4.2 t/ha harvested

in summer (February) and 5.6 t/ha harvested in winter (July). However, experience in

Western Australia suggests that D. hirsutum growth slows significantly during winter

(G.A. Moore, pers. comm.), which has not been documented in New Zealand, perhaps

because most DM measurements incorporated either spring or autumn growth into the

winter period. The optimum temperature for Dorycnium growth has not been

investigated, but it seems likely that temperatures during winter limit growth of D.

hirsutum.

For lucerne and other herbaceous pasture species both stem and leaf components of

biomass are edible, while in more shrubby species woody stem material can make up a

significant proportion of biomass. The woody component of ungrazed D. hirsutum

contributes greatly to plant biomass, making up as much as 89% of DM in summer

(Wanjiku et al. 1997). Douglas and Foote (1994) measured that leaf material made up

66% of the shoot biomass in D. hirsutum, 88% in D. pentaphyllum and 44% in D.


rectum in spring after 1 year of growth (Table 2). The proportion of leaf material

declined over the following summer in all species (Table 2). Another study measured

50% of leaf material in the DM of D. rectum (Waghorn et al. 1998). Woody

components in the biomass of Dorycnium need to be considered and management that

optimises digestible biomass production explored.

Grazing management

Once established, Dorycnium can withstand hard grazing (Sheppard and Douglas 1986).

Indeed regular grazing is recommended, as Dorycnium often becomes over-mature and

whole plants may die after flowering if not grazed (Wills 1983). In New Zealand,

Dorycnium may exhibit a relatively uniform growth year round, rather than seasonal

peak production like lucerne (Wills 1983). Thus, in New Zealand it has been suggested

that the role of D. hirsutum and D. pentaphyllum is to provide standing stock feed

during early spring and mid summer when other forage sources are in low supply (Wills

1983) and to supply nitrogen to cool season grasses (Douglas 1993). In southern

Australia, the greatest opportunity for Dorycnium is to provide forage in late summer

and autumn when little pasture is available and farmers rely on expensive

supplementary feed to maintain livestock (Bathgate and Pannell 2002). Lucerne can

greatly increase carrying capacity and farm profitability by providing feed during this

period (Crawford and MacFarlane 1995; Bathgate and Pannell 2002). However, lucerne

will produce little forage during long periods of minimal rainfall (Dolling et al. 2005).

Therefore pastures that can be managed as a standing ‘haystack’ would be a valuable

addition to farming systems in southern Australia.

Nitrogen fixation

Inoculation with appropriate root nodule bacteria and the ability of legumes to fix useful

amounts of nitrogen (N) are vital for plant productivity (Howieson 1999). Little work

has been conducted on N-fixation in Dorycnium. Rhizobium for Lotus corniculatus

produces effective nodules with Dorycnium species (Brockwell and Neal-Smith 1966;

Wills et al. 1989a). D. hirsutum appears to be non-specific in its Rhizobium

requirements and will form effective nodules with a range of strains of Rhizobium

isolated from diverse species of the Loteae tribe (Brockwell and Neal-Smith 1966).

Despite the ability of currently used strains of Rhizobium to form an effective

relationship with Dorycnium, little effort has been made to identify the most efficient

51

strains. Similarly, the tolerance of these strains to soil acidity and aluminium and their

survival in the soil has not been evaluated.

In a field study in New Zealand, Wanjiku et al. (1997) showed D. hirsutum to fix 71 kg

N/ha/year, with 98% of its annual N uptake from the atmosphere. The majority (55%) of

N was fixed between July and November and only 17% was fixed from November to

February (Wanjiku et al. 1997). The ability of Dorycnium to fix nitrogen has not been

investigated in Australia. Whilst N fixation will be crucial for Dorycnium productivity,

at a systems level it might not be as important as for annual pasture legumes.

Dorycnium pastures could incorporate annual legumes that could provide the N input

for subsequent crops or accompanying grasses. It has been suggested that deep rooted

perennial pastures may utilise excess N produced by the breakdown of annual pasture

legumes over summer; N would otherwise leach into subsoils and cause soil

acidification (Helyar 1976). The capacity of Dorycnium to provide this further benefit is

not known.

Considerations for animal production

By far the largest body of research on Dorycnium relates to forage value and covers

feed digestibility, protein content and condensed tannins. To date the majority of this

work has been conducted in New Zealand, with some information originating from

Europe and Tasmania.

Forage value

This section will concentrate on the most important traits in terms of animal production;

dry matter digestibility (DMD) and nitrogen (protein) content of forage. Information is

presented elsewhere on the elemental concentrations and the lignin and cellulose

content of D. rectum forage (Wills et al. 1989a; Wills et al. 1989b; Douglas et al.

1996a; Oppong et al. 2001; Waghorn and Molan 2001), and the amino acid and fatty

acid composition of D. pentaphyllum ssp. pentaphyllum forage (Viano et al. 1995).

Two documented studies have compared forage value among Dorycnium species.

Terrill et al. (1992) reported a high DMD and N content in edible material (leaf and soft

stem) of D. hirsutum, D. rectum and D. pentaphyllum (Table 3). However, these values

are much higher than those documented by other authors (Douglas et al. 1996a; Oppong


et al. 2001; Davies and Lane 2003). Terrill et al. (1992) do not document the

methodology used for DMD and total N analysis and values for DMD are high for all

forages (up to 85%). However, of the legumes tested, including Lotus spp., Hedysarum

coronarium, Astragalus cicer and Coronilla varia, D. hirsutum had the lowest DMD

(followed by D. rectum) and lowest N concentration.

DMD and total N content of Dorycnium species over a summer in Tasmania were

considerably lower than those documented by Terrill et al. (1992) (Table 4) (Davies and

Lane 2003). The highest DMD was measured in late spring (November to December)

and DMD then declined until the final sampling in April (Table 4). Davies and Lane

(2003) found the DMD of lucerne to be higher than for all Dorycnium species at all

times, peaking at 77% in September and declining to 60% in February.

Table 3. In-vitro DM digestibility (DMD), nitrogen concentration and extractable, bound and

total condensed tannin concentrations of Dorycnium spp. Values are for leaf and soft stem

harvested in late spring at Palmerston North, New Zealand. Adapted from Terrill et al. (1992).

Condensed tannin (% DM)

Species DMD (%)

Total N (g N/ kg

DM) Extractable Protein bound

Fibre bound

Total

Tannin: protein ratio

D. hirsutum 73 26 12.1 6.5 0.1 18.7 1.15

D. rectum 74 33 8.3 5.4 0.6 14.3 0.70

D. pentaphyllum 80 36 10.0 2.3 0.3 12.6 0.56

Table 4. Maximum and minimum in vitro dry matter digestibility (DMD) and total N content of

lucerne and three Dorycnium species grown in Tasmania (Davies and Lane 2003). Subscripts

indicate the month of sampling.

DMD (%) Total N (g N/kg DM) Species

Maximum Minimum Maximum Minimum

Lucerne 77 Sep 60 Feb 45 Sep 27 Feb

D. hirsutum 58 Nov 49 Apr 21 Sep 8 Apr

D. rectum 67 Nov 47 Apr 29 Dec 10 Apr

D. pentaphyllum 52 Dec 45 Apr 26 Sep 13 Apr

53

Other digestibility and N content measurements in New Zealand have been mainly

conducted on D. rectum and results are similar to those reported by Davies and Lane

(2003). Oppong et al. (2001) found D. rectum forage to have an organic dry matter

digestibility (OMD) of 66% and N content of 22 g N/kg DM in summer and autumn. D.

rectum leaf was more digestible and had a higher N content (OMD 87% and 33 g N/kg

DM) than edible stem (< 5 mm diameter) (OMD 46% and 12 g N/kg DM) (Oppong et

al. 2001). Waghorn and Molan (2001) also quote similar values for nitrogen content of

leaf (30 g N/kg DM) and stem (8 g N/kg DM). Douglas et al. (1996a) found the in vitro

organic dry matter digestibility (OMD) of D. rectum to be between 51 and 60% over

summer at a moist site but that it then declined to 43% in February at a drier site. The

protein content of the forage was also lower at the dry site (16–24 g N/kg DM) than the

moist site (25–37 g N/kg DM). This may be indicative of drought stress causing leaves

to be senesced and lower quality stem making up a greater proportion of the biomass

sampled.

Measurements of forage quality of Dorycnium in the literature indicate that it is lower

than currently grown perennial legumes. Davies and Lane (2002) found lucerne to have

a higher nutritive value than all Dorycnium species and in New Zealand, the nutritive

value of D. rectum was less than tagasaste (Chamaecytisus proliferus) and intermediate

between two Salix spp. (willows) (Douglas et al. 1996a; Oppong et al. 2001).

Dorycnium forage might be best utilised in summer and autumn when the value of dry

senesced annual pastures is also low. Current evidence suggests that Dorycnium forage

quality declines to levels around or below that which is sufficient for maintenance of

livestock (approx. 55% DMD) during summer. However, the components of Dorycnium

forage that are consumed by livestock (i.e. leaf or stem or woody stem) will greatly

influence the value of this feed.

Condensed tannins

Condensed tannins (CT) are secondary plant compounds which accumulate in plant

tissue as a defence strategy against pathogens, insects and herbivores (Barry and

McNabb 1999). Condensed tannins bind with plant, microbial and animal proteins. In

ruminants, this can reduce microbial digestion in the rumen, which may be beneficial to

reduce ammonia losses and increase the flow of amino acids into the small intestine (the

site of amino acid absorption) when dietary levels of CT are low (< 4%). Consequently,

improvements in animal live-weight gains and wool and milk production have been


recorded (Min et al. 2003). CT in animal diets also have anti-helminthic properties

(Molan et al. 2000) and can prevent bloat (Waghorn and Jones 1989). An in vitro assay

found that CT extracted from D. rectum leaf reduced the proportion of eggs of two

species of gastro-intestinal worms that hatched and completely prevented larval

development when incubate concentrations were > 400 µg CT/mL (Waghorn and Molan

2001). Lower solution concentrations of 100 µg CT/mL and 200 µg CT/mL reduced the

development of the worms to 44–33% and 9–5% of the control, respectively (Waghorn

and Molan 2001). Molan et al. (2000) found that CT had an inhibitory effect on the

migration of one species of gastro-intestinal worm, with CT from D. pentaphyllum

being more effective than Hedysarum coronarium, Onobrychis viciifolia, Lotus

pedunculatus, L. corniculatus and Rumex obtusifolius.

Despite the potential benefits of forages containing CT, levels of CT > 4–8% of DM in

temperate forages are detrimental to animal performance by reducing voluntary feed

intake and forage digestibility (Waghorn et al. 2002). High levels of CT have been

measured in Dorycnium by many authors; ranging from 13% in D. pentaphyllum

(Terrill et al. 1992) to 20% in D. rectum (Waghorn and Molan 2001) (Table 3). Other

temperate forage legumes included in the study of Terrill et al. (1992) had total CT

concentrations < 4.5% (Hedysarum coronarium), with the exception of Lotus

pedunculatus (7.7%). In fact, D. hirsutum was found to contain more CT than protein

(Table 3). Waghorn et al. (1998) found that the CT concentration was much higher in

the leaves of D. rectum (20%) than the stems (6%).

The high concentrations of CT in Dorycnium spp. have been shown to limit nutritive

value. Waghorn et al. (1998) found that when the effects of CT in D. rectum forage

(19% CT) were removed with polyethylene glycol (PEG) the DMD was increased from

59.6% to 63.6%, the nitrogen digestibility increased from 23.6% to 73.6% and animal

feed intake and live-weight gain also increased by > 10%.

The effects of CT are not only due to total concentration but also to the type of tannins

present. As in other forages with high tannin content, the majority of CT in Dorycnium

forage is unbound or extractable (Terrill et al. 1992). The unbound/protein bound CT

proportion has been measured to be 58/38% for D. rectum, 65/35% for D. hirsutum and

79/18% for D. pentaphyllum (Table 3) (Terrill et al. 1992). The remaining CT is fibre-

55

bound, which makes up a minor proportion (< 4%) of the total CT (Terrill et al. 1992).

Waghorn et al. (1998) found that in D. rectum 88% of CT were unbound. In its native

environment protein bound CT concentrations in D. pentaphyllum were 3.9, 2.7, 2.3 and

4.0% in winter, spring, summer and autumn, respectively (Barroso et al. 2001). Some

tannin compounds have greater effects than others; however the present understanding

of these effects is poor (Waghorn et al. 1998).

The high CT concentration in Dorycnium means its value as a fodder is limited to times

when feed shortages occur, otherwise livestock would need to be fed with other forages

to dilute the CT. Condensed tannins in forages can have beneficial effects on animal

health and performance when at nutritionally optimal levels (2–4% DM), but it is still

unclear how these might be achieved with Dorycnium spp. The presence of CT in

Dorycnium may afford resistance to attack from insects and disease pests of other

forage species (Barry and McNabb 1999). Genetic variation in CT content in

Dorycnium has not as yet been explored and may provide some opportunity for

improving their forage value.

Other anti-nutritional compounds

Apart from CT, other anti-nutritional compounds, such as photo-sensitising agents,

phyto-oestrogens and cyanogens are present in temperate legumes (Waghorn et al.

2002). No records exist of toxic or poisonous effects following the consumption by

animals of Dorycnium spp. Some species of the closely related Lotus genus accumulate

hydrocyanic acid (HCN) (Gebrehiwot and Beuselinck 2001). When concentrations

exceed 10 mg HCN/kg FW forages are considered to be cyanogenic and can be lethal to

animals (Davis 1991). Subspecies of D. pentaphyllum can contain low levels of HCN

(Plouvier 1974). Concentrations of 2.2–4.0 mg HCN/kg FW were measured in D.

suffriticosum (syn. of D. pentaphyllum ssp. pentaphyllum), 0.7–1.7 mg HCN/kg FW in

D. germanicum (syn. of D. pentaphyllum ssp. germanicum) and < 0.3 mg HCN/kg FW

in D. herbaceum (syn. of D. pentaphyllum ssp. herbaceum) (Plouvier 1974).

Flavonoids, potentially anti-nutritional compounds, have been documented in D. rectum

(Moreno et al. 2002) and D. suffruticosum (syn. of D. pentaphyllum ssp. pentaphyllum)

(Jay et al. 1978). Some anti-nutritional compounds may be found in Dorycnium but

these do not appear to be a major problem.


Palatability

Despite the high levels of CT, which can act to reduce forage palatability (Waghorn et

al. 2002), Dorycnium spp are reported to be palatable to stock (Wills 1983; Sheppard

and Douglas 1986). A study of palatability of woody fodder and pasture species in

south-east Spain found D. pentaphyllum to be highly palatable (90–100% of feed

offered to sheep was consumed) (Rios et al. 1989). Wills et al. (1999) found that D.

pentaphyllum was more palatable to sheep than D. hirsutum and its palatability was

comparable to lucerne, Trifolium ambiguum and Lotus corniculatus. Although D.

hirsutum was less palatable, significant variation among accessions was observed, with

accessions that possessed less leaf hairs grazed preferentially. D. rectum forage is also

readily grazed by sheep and goats when only average quality pasture is otherwise

available (Waghorn and Molan 2001). Although acceptable to livestock, Dorycnium are

likely to be less palatable to livestock than pastures with low CT levels (Barry and

McNabb 1999).

Conclusion and future research areas

A large amount of research is still required to understand where Dorycnium species can

best be used in Australia. Most agronomic information originates from New Zealand

and little data exists on how Dorycnium might perform under the conditions in the

agricultural regions of southern Australia. Dorycnium species originate in the

Mediterranean basin, an area that has provided a range of useful forage species for

Australia in the past. However, a detailed study of the native distribution of Dorycnium

species across the Mediterranean has not been conducted. This information would

enable the suitability of Dorycnium genotypes to Australian climates to be assessed and

could be used to target collections of Dorycnium from locations with the greatest

similarity to Australian conditions.

Based on reports from New Zealand, Dorycnium species appear to be tolerant of dry

seasonal conditions. In addition, Dorycnium appear to be more tolerant of stresses

associated with soil acidity than current lucerne cultivars. Thus, Dorycnium could play a

valuable role in the drier agricultural regions of southern Australia, where few perennial

legumes are suited, and where the use of lucerne is limited by soil acidity.

57

Despite the potential of Dorycnium to complement lucerne in the low rainfall

environments of southern Australia, information on the capacity of these plants to

increase water use and factors that will affect how they might be used in farming

systems needs to be obtained. No studies have recorded the rooting depth or measured

the water use of Dorycnium. Based on current knowledge, establishment appears to be a

limitation, but the reasons for this are unclear. Reliable establishment is vital for the use

of Dorycnium in rotation or phase farming systems. In New Zealand, Dorycnium are

endorsed as drought forage and they might play a similar role in Australia. Poor forage

quality in Dorycnium is a major limitation. Thus, the provision of green feed when

forage from other sources is scarce provides the greatest opportunity. However, the

accumulation of woody biomass in Dorycnium poses a challenge to their management.

It is unlikely that Dorycnium will provide a replacement for lucerne, where lucerne is

currently productive. Dorycnium will need to fill niches where current lucerne cultivars

are not well adapted (e.g. acidic soils) and provide benefits for livestock production,

such as animal health and/or continuity of feed supply, if wide-scale adoption is to

occur. Cheap and easy establishment methods will need to be developed for Dorycnium

to be used as a phase pasture in rotation with crops in a similar way to lucerne;

otherwise the use of Dorycnium will be limited to permanent pastures, long-term

rotations or alley cropping systems. Despite these considerations, if Dorycnium can

provide some economic benefit to farmers and appropriate farming systems are

developed then it may be a useful tool for farmers in southern Australia to compliment

lucerne for salinity management.

References

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Barroso FG, Martinez TF, Paz T, Parra A, Alarcon FJ (2001) Tannin content of grazing plants of southern Spanish arid lands. Journal of Arid Environments 49, 301-314. Barry TN, McNabb WC (1999) The implications of condensed tannins on the nutritive value of temperate forages fed to ruminants. British Journal of Nutrition 81, 263-272. Bathgate A, Pannell DJ (2002) Economics of deep-rooted perennials in western Australia. Agricultural Water Management 53, 117-132. Bennett SJ (2002) Distribution and economic importance of perennial Astragalus, Lotus and Dorycnium. In 'New Perennial Legumes for Sustainable Agriculture'. (Ed. SJ Bennett) pp. 90-115. (University of Western Australia Press: Crawley, Western Australia) Bennett SJ, Ayres JF, Dear BS, Ewing MA, Harris C, Hughes S, Mitchell M, Moore GA, Nie Z, Reed K, Sandral GA, Slattery J, Snowball R (2003) 'Perennial pastures for the recharge areas of southern Australia.' CRC for Plant-based Management of Dryland Salinity, Perth, Australia. Brockwell J, Neal-Smith CA (1966) 'Effective nodulation of hairy canary clover, Dorycnium hirsutum (L.) Ser. in DC.' CSIRO Division of Plant Industry Field Station Record, 5 (1). Cocks PS (2001) Ecology of herbaceous perennial legumes: a review of characteristics that may provide management options for the control of salinity and waterlogging in dryland cropping systems. Australian Journal of Agricultural Research 52, 137-151. Cooper CS (1977) Growth of the legume seedling. Advances in Agronomy 29, 119-139. Crampton B (1946) Hairy canary clover. Californian Agriculture 18, 12-13. Cransberg L, McFarlane DJ (1994) Can perennial pastures provide the basis for a sustainable farming system in southern Australia? New Zealand Journal of Agricultural Research 37, 287-294. Crawford MC, MacFarlane DJ (1995) Lucerne reduces soil moisture and increases livestock production in an area of high groundwater recharge potential. Australian Journal of Experimental Agriculture 35, 171-180. Davies SR, Lane PA (2003) Seasonal changes in feed quality of Dorycnium spp. In 'Proceedings of the 11th Australian Agronomy Conference'. Geelong, Victoria. (Eds M Unkovich, GJ O'Leary). (The Australian Society of Agronomy) Davis RH (1991) Cyanogens. In 'Toxic Substances in Crop Plants'. (Eds JP DeMello, F DeMello, CM Duffus, JM Duffus) pp. 202-225. (Royal Society of Chemistry: Cambridge) Dear BS, Moore GA, Hughes SJ (2003) Adaptation and potential contribution of temperate perennial legumes to the southern Australian wheatbelt: a review. Australian Journal of Experimental Agriculture 43, 1-18.

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ILDIS (2004) Legume Web. International Legume Database and Information Service World Database of Legumes, version 6.05. Available: http://biodiversity.soton.ac.uk/LegumeWeb (9 June 2004) Jay M, Hasan A, Voirin B, Favre-Bonvin J, Viricel MR (1978) The flavonoids of Dorycnium suffruticosum and Tetragonolobus siliquosus (Leguminosae). Phytochemistry 17, 1196-1198. Lane PA, Davies SR, Hall EJ, Moore GA (2004) 'Dorycnium species as alternative forage plants.' Rural Industries Research and Development Corporation, Report number 04/159. Min BR, Barry TN, Attwood GT, McNabb WC (2003) The effect of condensed tannins on the nutrition and health of ruminants fed fresh temperate forages: a review. Animal Feed Science Technology 106, 3-19. Molan AL, Waghorn GC, Min BR, McNabb WC (2000) The effect of condensed tannins from seven herbages on Trichostrongylus colubriformis larval migration in vitro. Folia Parisitologica 47, 37-44. Moreno A, Martin-Cordero C, Iglesias-Guerra F, Toro MV (2002) Flavonoids from Dorycnium rectum. Biochemical Systematics and Ecology 30, 73-74. Oppong SK, Kemp PD, Douglas GB, Foote AG (2001) Browse yield and nutritive value of two Salix species and Dorycnium rectum in New Zealand. Agroforestry Systems 51, 11-21. Perez Arquillue C, Gomez Ferreras C (1986) Pollen analysis of Diplotaxis erucoides honeys from Los Monegros, Spain. [Spanish]. In 'Actas del VI Simposio de Palinologia'. A.P.L.E, Salamanca, Spain pp. 231-238 Petkov V (1977) Investigation of the nectar-producing qualities of some forage plants. Rastenievudni Nauki 14, 123-133. Plouvier V (1974) Cyanogenetic heterosides and enzymes: dhurroside in Macadamia ternifolia (Proteacea), hydrocyanic acid in Dorycnium (Leguminoseae), the distribution of linamarase. Comptes Rendus Hebdomadaires des Seances de l'Academie des Sciences 279, 1689-1692. Reid R (1995) New and novel temperate legumes for ornamental and landscape horticulture. In 'Proceedings of the International Plant Propagators' Society' pp. 94-96 Ridley AM, Christy B, Dunin FX, Haines PJ, Wilson KF, Ellington A (2001) Lucerne in crop rotations on the Riverine Plains 1. The soil water balance. Australian Journal of Agricultural Research 52, 263-277. Rios S, Correal E, Robledo A (1989) Palatability of the main fodder and pasture species present in S.E. Spain: I. Woody species (trees and shrubs). In 'Proceedings of XVI International Grassland Congress'. Nice, France p. 1531. (Association Francaise pour la Production Fourragere, Centre National de Recherche Agronomique, Versailles, France)

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Sala Llinares A (1989) Honeys of the Spanish Mediterranean: palynological studies. Vida Apicola 37, 47-51. Schachtman DP, Kelman WM (1991) Potential of Lotus germplasm for the development of salt, aluminium and manganese tolerant pasture plants. Australian Journal of Agricultural Research 42, 139-149. Sheppard JS, Douglas GB (1984) Canary clovers. Streamland 32, 4-8. Sheppard JS, Douglas GB (1986) Management and uses of Dorycnium spp. Water and Soil Miscellaneous Publication 94, 260-262. Slavik B (1995) A plant-geographical study of the genus Dorycnium Mill, (Fabaceae) in the Czech Republic. Folia Geobotanica and Phytotaxonomica 30, 291-304. Tasenkevich L (1994) Dorycnium pentaphyllum subsp. patenti-pilosum (Fabaceae) in the Eastern Carpathians of Ukraine. Fragmenta Floristica et Geobotanica 39, 549-554. Terrill TH, Rowan AM, Douglas GD, Barry TN (1992) Determination of extractable and bound condensed tannin concentrations in forage plants, protein concentrate meals and cereal grains. Journal of the Science of Food and Agriculture 58, 321-329. Viano J, Masotti V, Gaydou EM, Bourreil PJL, Ghiglione C, Giraud M (1995) Compositional characteristics of 10 wild plant legumes from Mediterranean French pastures. Journal of Agricultural and Food Chemistry 43, 680-683. Waghorn GC, Adams NR, Woodfield DR (2002) Deleterious substances in grazed pastures. In 'Sheep Nutrition'. (Eds M Freer, H Dove) pp. 333-356. (CSIRO Publishing: Collingwood, Australia) Waghorn GC, Douglas GB, Niezen JH, McNabb WC, Foote AG (1998) Forages with condensed tannins - their management and nutritive value for ruminants. Proceedings of the New Zealand Grassland Association 60, 89-98. Waghorn GC, Jones WT (1989) Bloat in cattle. 46 - Potential of dock (Rumex obtusifolius) as an antibloat agent for cattle. New Zealand Journal of Agricultural Research 32, 227-235. Waghorn GC, Molan AL (2001) Effect of condensed tannins in Dorycnium rectum on its nutritive value and on the development of sheep parasite larvae. Proceedings of the New Zealand Grassland Association 63, 273-277. Wanjiku J, Mead DJ, Goh KM, Gadgil RL (1997) Biological nitrogen fixation by three legumes in coastal sand-dune forest, estimated by an isotope dilution technique. New Zealand Journal of Forestry Science 27, 39-50. Ward PR, Dolling PJ, Dunin FX (2003) The impact of a lucerne phase in a crop rotation on groundwater recharge in south-west Australia. In 'Proceedings of the 11th Australian Agronomy Conference'. Geelong, Victoria. (Eds M Unkovich, GJ O'Leary). (Australian Society of Agronomy)


Wheeler DM, Dodd MB (1995) Effect of aluminium on yield and plant chemical concentrations of some temperate legumes. Plant and Soil 173, 133-145. Wills BJ (1983) 'Forage plants for the semi-arid high country and rangelands of New Zealand.' Centre of Resource Management, Lincoln College, Special Publication 26, Canterbury, New Zealand. Wills BJ (1984) Alternative plant species for revegetation and soil conservation in the tussock grasslands of New Zealand. Tussock Grasslands and Mountain Lands Institute Review 42, 49-58. Wills BJ, Begg JSC, Foote AG (1989a) Dorycnium species - Two new legumes with potential for dryland pasture rejuvenation and resource conservation in New Zealand. Proceedings of the New Zealand Grassland Association 50, 169-174. Wills BJ, Begg JSC, Sheppard JSS (1989b) Dorycnium and other Mediterranean species - their use for forage and soil conservation in semi-arid environments in New Zealand. In 'Proceedings of XVI International Grassland Congress'. Nice, France p. 1517. (Association Francaise pour la Production Fourragere, Centre National de Recherche Agronomique, Versailles, France) Wills BJ, Trainor KD (2000) Successful drilling of forage species during severe drought in Central Otago - a preliminary report 1998/99. Proceedings of the New Zealand Grassland Association 62, 207-211. Wills BJ, Trainor KD, Littlejohn RP (2004) Semiarid land rehabilitation by direct drilling in the South Island, New Zealand - Plant species and establishment technology. Land Degradation and Development 15, 1-14. Woodgate K, Maxted N, Bennett SJ (1999) A generic conspectus of the forage legumes of the Mediterranean basin. In 'Genetic Resources of Mediterranean Pasture and Forage Legumes'. (Eds SJ Bennett, PS Cocks). (Kluwer Academic Publishers: London) Woodman RF, Keoghan JM, Allan BE (1992) Pasture species for drought-prone lower slopes in the South Island high country. Proceedings of the New Zealand Grassland Association 54, 115-120.

Chapter 3: Germplasm collections, eco-geography and climate

match modelling to southern Australia for Dorycnium

species

Abstract

This study aimed to assess the current genetic resources of Dorycnium and using an

ecogeographical analysis, determine the key ecological factors that might influence their

potential adaptation to agricultural regions of southern Australia. Current genetic

resources of Dorycnium taxa in Australia and New Zealand was surveyed and locations

of herbarium and germplasm collections were collated. The quantity of accessions of

Dorycnium are very limited due to the lack of systematic collection of diversity for plant

breeding. Currently, only 58 non-duplicated accessions of 4 species in the Dorycnium

genus are held in genetic resource centres in Australia. Passport data for Dorycnium

entries in gene banks is scarce and limited site description information is available from

herbarium collections. Thus, little ecological information related to climate and soil

requirements of Dorycnium species could be obtained from these sources.

Climate comparisons between the native distribution of Dorycnium species and

Australia were made using spatial aridity data and CLIMEX climate match modelling.

This revealed that Dorycnium rectum and D. hirsutum originate from regions with

climatic conditions most similar to the temperate pasture zone in southern Australia.

Some D. pentaphyllum germplasm was equally correlated, but D. graecum was poorly

matched. The wide distribution of D. rectum, D. hirsutum and D. pentaphyllum across

the Mediterranean basin suggests that significant genetic diversity might be available in

these species that may not be represented in current collections. Targeted collections in

Spain, Italy, Greece and Sardinia at sites with greatest similarity to intended production

environments in southern Australia are likely to introduce better adapted germplasm

than the material currently available.

Chapter 3: Germplasm collections and eco-geography of Dorycnium spp. 64

Introduction

Dorycnium species are widely distributed through the Mediterranean basin, a region that

has supplied valuable pasture plants for southern Australia in the past (Cocks 1993).

They are perennial legumes that appear to have potential as forage plants in southern

Australia (Chapter 2; Bennett 2002; Dear et al. 2003). Development of sustainable land

uses to deal with issues such as dryland salinity has encouraged the exploration of a

range of new perennial forage species including Dorycnium to help overcome these

challenges (Cocks 2001; Bennett et al. 2003). However, species of Dorycnium have not

been domesticated for commercial use and to our knowledge Dorycnium have never

been the target of collection trips. Knowledge about the ecology of Dorycnium is

limited by the lack of systematic documentation and germplasm collection.

Taxonomy of Dorycnium is complicated by many name changes and synonymous

nomenclature in the literature (Chapter 2). However, four main species are accepted; D.

hirsutum, D. rectum, D. pentaphyllum and D. graecum (Table 1) (Ball 1968). D.

hirsutum and D. rectum are widely distributed throughout Mediterranean Europe, West

Asia and North Africa (Greuter et al. 1989). D. graecum is found in the eastern

Mediterranean and around the Caspian Sea (Greuter et al. 1989). D. pentaphyllum, in

addition to Mediterranean regions, is found in more temperate areas in central and

eastern Europe. Many subspecies have been described in the D. pentaphyllum complex

(Table 1), some of which are classified at the species level by some authors. D. hirsutum

and D. pentaphyllum are typically found on dry slopes, pastures and thickets on a range

of soils (Demiriz 1970), D. rectum occurs in damp bushy areas (Demiriz 1970) or

adjacent to swamps and water courses (Zohary 1972; Meikle 1977), while D. graecum

is found in a range of habitats ranging from forests to thickets on open slopes (Demiriz

1970).

Other less known species of Dorycnium, including D. amani Zohary and D. axilliflorum

Hub.-Mor., have been excluded from this study as there is too little information

available on their ecological and geographic distribution.

65

Table 1. Taxonomy of the Dorycnium genus. Adapted from Demiriz (1970) and Ball (1968).

Family – Fabaceae

Subfamily – Papilionoideae

Tribe – Loteae

Genus – Dorycnium Miller

Section

A. Bonjeania

D. hirsutum (L.) Ser.

D. rectum (L.) Ser.

D. graecum (L.) Ser.

B. Dorycnium

D. pentaphyllum Scop.

ssp. pentaphyllum

ssp. gracile Gremli

ssp. germanecum Jordan

ssp. herbaceum Vill.

ssp. anatolicum Boiss.

ssp haussknechtii Boiss.

A greater understanding of the ecology of Dorycnium can be gained through the use of

eco-geographical analysis. It was the aim of this study to determine some key ecological

factors affecting the distribution of Dorycnium species and infer from these their

potential adaptation to the agricultural regions of southern Australia. Initially, it was

hoped to use herbarium records and genebank passport data to obtain climatic and

edaphic conditions at collection sites (Bennett 1999). However, site descriptions

contained in passport data or herbarium collections of Dorycnium species were

extremely limited and precluded this approach. Thus, an alternative approach involving

use of spatial GIS data to obtain information for previous collection locations of

Dorycnium was attempted. However, with the exception of one set of data that

described climate aridity, GIS data was also hard to locate and had limited relevance or

insufficient spatial differentiation to provide a useful basis for analysis. Consequently,

aridity information was generated for the collection locations of Dorycnium taxa and

climate match modelling with CLIMEX (Sutherst and Maywald 1999) was used to

predict the potential climatic regions of Australia where Dorycnium species might be

best suited.


Materials and method

Germplasm collections

Passport data, entry codes and donor or origin of entries was obtained for collected

Dorycnium germplasm held in genetic resource centres; AgResearch 'Margot Forde'

Germplasm Centre, New Zealand (Warren Williams, pers. comm.), Australian

Medicago Genetic Resource Centre (Steve Hughes, pers. comm.), Australian Trifolium

Genetic Resource Centre (Richard Snowball, pers. comm.), Tasmania Institute of

Agricultural Research collection (Eric Hall, pers. comm.) and the Royal Botanic

Gardens, Kew, United Kingdom. Significant interchange of germplasm between genetic

resource centres was evident, thus duplicate entries were removed based on donor or

entry code details.

Collection sites of Dorycnium taxa

The lack of passport information for Dorycnium germplasm held in the genetic resource

centres meant that additional ecological information was sought from herbarium

collections. Records of collection sites for Dorycnium taxa, including all those labelled

as synonyms, were obtained from the Flora of Turkey and the East Aegean Islands

(Demiriz 1970), Flora Palaestina (Zohary 1972), Flora of Iraq (Townsend 1974), Flore

de la Tunisie (Pottier-Alapetite 1979), Flora of Syria, Palestine and Sinai (Post and

Dinsmore 1933), Flora of Cyprus (Meikle 1977) and online at the Global Biodiversity

Information Facility Data Portal (GBIF Data Portal 2005). Where longitude and latitude

coordinates were not provided, these were obtained from the location of nearby towns

and/or provinces where Dorycnium were collected using atlas records from each

country. Altitude of collection sites was recorded when this information was available.

The distribution of Dorycnium taxa was mapped using ArcGIS 8 software (ESRI 2000).

Climate aridity comparisons

Spatial data of an aridity index (Equation 1) for Europe, western Asia and northern

Africa was sourced from online databases (DISMED 2003). Aridity index values were

obtained for longitude and latitude coordinates of Dorycnium collection locations using

ArcGIS software, ArcView (ESRI 2000). Spatial aridity data (Equation 1) was

developed for Australia from annual rainfall and potential evapo-transpiration metadata

(National Land and Water Resources Audit Metadata 2001). Regions with

67

corresponding aridity index values in Australia were then mapped also using ArcGIS

software (ESRI 2000).

annual precipitation (1) Aridity index =

annual potential evapo-transpiration

Climate match modelling

The climate matching function in CLIMEX (Sutherst and Maywald 1999) was used to

make comparisons between European and Australian locations. Default values, i.e.

equal weighting between maximum and minimum temperature, total rainfall and rainfall

pattern indices, were used in the computation of the total climate match index (MI).

Locations for Dorycnium collections were matched to the nearest European location for

which data was available in CLIMEX using ArcView. A climate match to Australian

locations was then run for each European site. Suitability of each Dorycnium taxa to

Australian locations was calculated based on the average climate match index for all

collection sites. European locations with the highest climate match index were

determined for 4 Australian locations with a climate indicative of the main agro-climatic

groups in the agricultural region of southern Australia (Table 2 and Fig. 1) (Hutchinson

et al. 2005).

Table 2. Location and long-term mean annual rainfall (MAR) of towns used for CLIMEX

climate matching to European locations. Towns were chosen as examples of agro-climatic

regions in Australia (Hutchinson et al. 2005).

Agro-climate Code Town Latitude Longitude Elevation (m)

MAR (mm)

Wet Mediterranean

E1 Keith, SA 36º06’ S 140º21’ E 29 466

Dry Mediterranean

E2 Hyden, WA

32º27’ S 118º54’ E 299 344

Temperate, subhumid

E3 Forbes, NSW

33º23’ S 148º00’ E 240 526

Temperate, cool season wet

D5 Hamilton, Victoria

37º44’ S 142º01’ E 209 688


Figure 1. Distribution of agro-climatic classes in southern Australia and example locations used

in CLIMEX modelling (Table 1) (Hutchinson et al. 2005). No locations are presented from the

subtropical, subhumid agro-climate group as they were poorly matched to European locations.

Results

Germplasm collections

The number of Dorycnium germplasm accession entries in Australia and New Zealand

genetic resource centres was 117 for D. hirsutum, 94 for D. pentaphyllum, 29 for D.

rectum and 1 for D. graecum. However, many of these appear to be duplicated amongst

the various centres. The New Zealand collection is the largest and lists multiple entries

for seed lots from breeding lines. It is therefore difficult to establish the true diversity of

Dorycnium available. In Australia, there appears to be 28 non-duplicated accessions of

D. hirsutum, 23 of D. pentaphyllum, 6 of D. rectum and 1 of D. graecum. The origin of

these collections is also limited and little associated passport data is available (Table 3).

Collection sites of Dorycnium taxa

Analysis of collection sites revealed distinct distributions for some Dorycnium taxa. D.

hirsutum and D. rectum revealed a similar distribution and were located mainly in

coastal regions, suggesting a preference for low altitudes (Fig. 2a and 2b). This is

confirmed with the altitude data obtained for some collection sites (Table 4). D.

Hyden, WA

Keith, SA

Hamilton, Vic

Forbes, NSW Maitland, SA

D5 - Temperate, cool season wet E1 - Wet Mediterranean

E3 - Temperate, subhumid

Agro-climatic classes

E4 - Subtropical, subhumid

E2 – Dry Mediterranean

69

pentaphyllum has a much wider distribution including central Europe, central Spain,

throughout Turkey and into West Asia (Fig. 2c). However, D. hirsutum and D. rectum

appear to be more abundant in the Greek Islands than D. pentaphyllum. D. graecum

displayed a much narrower distribution than the other 3 species and has only been found

in eastern Greece, Turkey and Syria (Fig. 2d). Collection locations of D. graecum also

indicate that this species occurs in highland regions at higher altitudes than D. hirsutum

and D. rectum (Table 4). In all species, accessions with location details originated

mainly from Italy and Greece and do not fully represent their distribution range (Fig. 2).

Table 3. The number of non-duplicated accessions of Dorycnium species held in Australia and

the number of these that have position, soil or climate data on the site of collection.

Species Accessions held in

Australia

No. of countries

represented

Longitude/ Latitude

data

Site soil data

Site climate data

D. hirsutum 28 2 8 2 2

D. rectum 6 4 1 0 0

D. pentaphyllum 23 7 5 1 1

D. graecum 1 n/a 0 0 0

n/a, no records available

Table 4: The range and median elevation where Dorycnium taxa have been collected (n =

number of records).

Elevation (m) Species

Range Median n

D. hirsutum 0–950 222 20

D. rectum 100–730 100 5

D. graecum 150–1750 1150 15

D. pentaphyllum 100–1800 975 32

ssp herbaceum 150–1100 475 6

ssp anatolicum 100–1500 1175 10

ssp haussknechtii 300–1800 965 16

ssp. gracile n/a –

ssp pentaphyllum n/a –

ssp. germanicum n/a –

n/a, no records available


Figure 2. Map of the Mediterranean region showing the collection locations of (a) Dorycnium hirsutum, (b) D. rectum, (c) D. pentaphyllum and (d) D. graecum herbarium specimens (●) including accessions held in Australian and New Zealand genetic resource centres ( ).

(a) D. hirsutum

(b) D. rectum

(c) D. pentaphyllum

(d) D. graecum

71

The subspecies of D. pentaphyllum showed a distinct separation across the

Mediterranean (Fig. 3). The centre of origin of D. pentaphyllum ssp. gracile and ssp.

pentaphyllum collections were distinct from other subspecies, located only in western

regions of the Mediterranean. D. pentaphyllum ssp. gracile was only found in Spain,

while D. pentaphyllum ssp. pentaphyllum was also found in southern France, Italy and

Tunisia. D. pentaphyllum ssp. germanicum and ssp. herbaceum were found through

central Europe and mainland Greece, with D. pentaphyllum ssp. herbaceum also found

in Turkey and into the Caucasus-Caspian region. D. pentaphyllum ssp. anatolicum was

limited to, but widely distributed across, Turkey and D. pentaphyllum ssp. haussknechtii

was found only in southern Turkey and coastal regions of Syria and Lebanon. No

information was available on the altitude of collection sites for D. pentaphyllum ssp.

pentaphyllum, ssp. gracile and ssp. germanicum. D. pentaphyllum ssp haussknechtii and

D. pentaphyllum ssp. anatolicum were frequently found in highland regions > 1000 m

above sea level, while ssp. herbaceum was generally found at lower altitudes (Table 4).

Figure 3. Map of the Mediterranean region showing the collection locations of D. pentaphyllum

subspecies; (∆) subsp. pentaphyllum, (●) subsp. gracile, (■) subsp. germanicum, (○) subsp.

herbaceum, (□) subsp. anatolicum and (▲) subsp. haussknechtii.

Climate aridity comparisons

Climate aridity was not closely related to the distribution of taxa and no distinct

ecological segregation was obvious between Dorycnium taxa. Dorycnium species were

found across the range of climatic aridity indexes (Fig. 4). Despite this variation the

majority of Dorycnium were collected in regions with lower annual precipitation than

potential evapo-transpiration (i.e. aridity index < 1.0) (Fig. 4). However, D. graecum

was not found at locations with a climate aridity index of < 0.5 and a larger proportion


of D. graecum occurrences (> 30%) were found at locations with aridity indexes > 2.0

(Fig. 4). The climatic aridity range of D. graecum suggests that its suitability to drier

regions of Australia is limited (Fig. 5d). D. rectum, D. hirsutum and D. pentaphyllum

were found at sites with aridity indexes down to 0.3 (Fig. 4) indicating that these species

may possess germplasm adapted to arid climates comparable to those in agricultural

regions of Australia (Fig. 5a–c).

Figure 4. Occurrence frequency of climate aridity index for collection locations of (a) D.

hirsutum (n=194), (b) D. rectum (n=158), (c) D. pentaphyllum (n=26) and (d) D. graecum

(n=26).

(a) D. hirsutum

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35

>0.20.2-0.3

0.3-0.40.4-0.50.5-0.60.6-0.7

0.7-0.80.8-0.90.9-1.01.0-1.2

1.2-2.0>2.0

Arid

ity in

dex

Proportion of occurences(c) D. pentaphyllum

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35

>0.20.2-0.30.3-0.4

0.4-0.50.5-0.60.6-0.70.7-0.80.8-0.90.9-1.0

1.0-1.21.2-2.0

>2.0

Arid

ity in

dex

Proportion of occurences

(b) D. rectum

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35

>0.20.2-0.30.3-0.4

0.4-0.50.5-0.60.6-0.70.7-0.80.8-0.90.9-1.0

1.0-1.21.2-2.0

>2.0

Arid

ity in

dex

Proportion of occurences(d) D. graecum

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35

>0.20.2-0.30.3-0.4

0.4-0.50.5-0.60.6-0.70.7-0.80.8-0.90.9-1.0

1.0-1.21.2-2.0

>2.0

Arid

ity in

dex

Proportion of occurences

73

Figure 5. Climate aridity index comparison between Australia and locations where (a) D.

hirsutum, (b) D. rectum, (c) D. pentaphyllum and (d) D. graecum have been collected in their

native distribution. Black regions indicate values between quartile 1 and 3 and grey regions

indicate values between the minimum and quartile 1 of occurences for each species.

Climate match modelling

Climate match modelling revealed that climatic conditions in the native distribution of

D. rectum and D. hirsutum were most similar to locations in southern Australia (Fig. 6a

and 6b). The climate match index between collection locations for both species in

Europe and Australia was highest at Maitland in South Australia (67 MI), but other sites

in south-west Western Australia and southern South Australia also produced a high

match.

Collections of D. graecum had a poor match to climates in southern Australia (Fig. 6d).

Climate match indices for D. pentaphyllum were generally lower than for D. hirsutum

and D. rectum (< 65 MI) (Fig. 6c). However, taxa within D. pentaphyllum exhibited

differences in climate match suitability (Fig. 7). D. pentaphyllum ssp. germanicum had

the highest climate match; but this analysis was based on only a few collection sites

(Fig. 7d). Climate matches for D. pentaphyllum ssp. pentaphyllum were similar to those

(d) D. graecum

(b) D. rectum

(c) D. pentaphyllum

(a) D. hirsutum


for D. hirsutum and D. rectum (Fig. 7a), while D. pentaphyllum ssp. gracile and ssp.

anatolicum (Fig. 7b and 7e) were well matched to few locations.

(a) D. hirsutum (b) D. rectum

(d) D. graecum (c) D. pentaphyllum

Figure 6. Average climate match index (%) generated from CLIMEX (55–60 (○), 60–65 ( ),

65–70 (●)) for Australian locations matched with nearest European locations to collection sites

of (a) D. hirsutum (n=194), (b) D. rectum (n=157), (c) D. pentaphyllum (n=360) and (d) D.

graecum (n=26) (n=number of records used). Australian locations with MI < 55 are not

presented.

The native distribution of D. hirsutum, D. rectum and D. pentaphyllum (Fig. 2)

corresponded to European locations with a high climate correlation to towns

representing 3 of the 4 main agro-climatic groups in southern Australia (Fig. 8); Keith,

SA (wet Mediterranean), Hyden, WA (dry Mediterranean) and Forbes, NSW

(temperate, sub-humid). Dorycnium species did not occur as frequently at European

locations with a high match to the mildest climate of these sites, Hamilton, Victoria

(temperate, cool season wet) (Fig. 8d).

75

Figure 7. Average climate match index generated from CLIMEX (%) (55–60 (○), 60–65 ( ),

65–70 (●) and > 70 (▼)) for Australian locations matched with nearest European locations to

collection sites of D. pentaphyllum subspecies; (a) pentaphyllum (n=58), (b) gracile (n=36), (c)

herbaceum (n=49), (d) germanicum (n=6), (e) anatolicum (n=11) and (f) haussknechtii (n=36)

(n=number of records used). Australian locations with MI < 55 are not presented.

(c) herbaceum

(b) gracile

(e) anatolicum (f) haussknechtii

(d) germanicum

(a) pentaphyllum


Figure 8. European locations with a climate match index of 70–75 (○) and > 75 (●) to (a) Keith, South Australia, (b) Hyden, Western Australia, (c) Forbes, New South Wales and (d) Hamilton, Victoria. Australian sites were chosen to represent key agro-climatic regions of southern Australia (Hutchinson et al. 2005).

(a) E1 – Keith, SA

(b) E2 – Hyden, WA

(c) E3 – Forbes, NSW

(d) D5 – Hamilton, Vic

77

Discussion

The results of this study suggest that the Dorycnium genus contains species that might

be adapted to climatic conditions in southern Australia. D. hirsutum and D. rectum

appear to originate from regions with the greatest similarity to southern Australian

climates. Climate match modelling demonstrated that the potential distribution of these

species corresponds with the temperate pasture adaptation zone in eastern and western

Australia, described by Hill (1996). Locations with the highest match for D. hirsutum

and D. rectum occurred in regions with low to medium rainfall (300–550 mm mean

annual rainfall) Mediterranean-type climates. In addition, both species occur near

locations with a high climate match to towns representing dry and wet Mediterranean

agro-climatic groups (Fig. 2 and Fig. 8). In spite of promising climate comparison

between the native distribution of D. rectum and Australian environments, D. rectum is

said to occur mainly in damp sites or near sources of water (Demiriz 1970), thus D.

rectum may only occur in moist sites within drier environments. Further investigations

are required to ascertain the tolerance of D. rectum to water limited environments.

D. graecum appears to be poorly suited to drier climatic conditions of southern

Australia and mainly occurs at higher altitudes and in more humid climates. Its

adaptation to Australia seems to be inferior to other species in Dorycnium.

Overall, D. pentaphyllum collection locations had a lower climate match to locations in

southern Australia than D. hirsutum and D. rectum. However, geographic segregation of

taxa in the D. pentaphyllum complex suggests that the subspecies might differ in their

ecological requirements. Climate matching suggested that D. pentaphyllum ssp.

germanicum originates from climatic conditions with the greatest similarity to the

temperate pasture zone of southern Australia (Hill 1996). However, care must be taken

with this interpretation, as it is based on only 6 collections. Based on many more

collections (58 and 49, respectively), D. penatphyllum ssp. pentaphyllum and ssp.

herbaceum matched to similar Australian locations to D. hirsutum and D. rectum. D.

pentaphyllum ssp. pentaphyllum also occurs in regions with the highest climate

correlation to Australian sites representing wet and dry Mediterranean and temperate,

subhumid climates. This suggests that this subspecies of D. pentaphyllum might have

the greatest potential in southern Australia. In the past, ecological and agronomic

evaluation of D. pentaphyllum has not identified the subspecies under examination and


this information is not provided for most collected germplasm. Thus, identification of

D. pentaphyllum to subspecies might enable selection of better suited genotypes in

future evaluation programs.

The current holdings of Dorycnium in genetic resource centres are small and likely to

represent a fraction of the available genetic diversity. Interest in the domestication of

Dorycnium genus has arisen only recently and little germplasm has been collected and

described. Thus, current evaluation of the species is limited to a small number of

accessions of poorly documented origin. Future development of Dorycnium would

require a far greater genetic resource base. The wide distribution of D. rectum, D.

hirsutum and D. pentaphyllum across the Mediterranean and their occurrence in

environments with similar climatic conditions to southern Australia provides an

opportunity to target collections to regions most likely to yield adapted germplasm.

Knowledge of the key ecological factors affecting the distribution of Dorycnium species

would be valuable to future domestication initiatives. However, the acute lack of site

description data from herbarium or collection sites made this task impossible from

currently available information. Significant opportunities exist to improve our

understanding of the impact of climate and soils on ribution in the Dorycnium genus.

References

Ball PW (1968) Dorycnium Miller. In 'Flora Europaea'. (Eds TG Tutin, VH Heynood, NA Burgess, DM Moore, DH Valentine, SM Walters, DA Webb) pp. 172. (Cambridge University Press: London) Bennett SJ (1999) Using collections to describe ecological relationships. In 'Genetic resources of Mediterranean Pasture and Forage Legumes'. (Eds SJ Bennett, PS Cocks) pp. 41-52. (Kluwer Academic Publishers: Dordrecht, Netherlands) Bennett SJ (2002) Distribution and economic importance of perennial Astragalus, Lotus and Dorycnium. In 'New Perennial Legumes for Sustainable Agriculture'. (Ed. SJ Bennett) pp. 90-115. (University of Western Australia Press: Crawley, Western Australia) Bennett SJ, Ayres JF, Dear BS, Ewing MA, Harris C, Hughes S, Mitchell M, Moore GA, Nie Z, Reed K, Sandral GA, Slattery J, Snowball R (2003) 'Perennial pastures for the recharge areas of southern Australia.' CRC for Plant-based Management of Dryland Salinity, Perth, Australia.

79

Cocks PS (1993) 'Legumes from the Mediterranean basin: a continuing source of agricultural wealth for southern Australia.' Co-operative Research Centre for Legumes in Mediterranean Agriculture, No. 1. Cocks PS (2001) Ecology of herbaceous perennial legumes: a review of characteristics that may provide management options for the control of salinity and waterlogging in dryland cropping systems. Australian Journal of Agricultural Research 52, 137-151. Dear BS, Moore GA, Hughes SJ (2003) Adaptation and potential contribution of temperate perennial legumes to the southern Australian wheatbelt: a review. Australian Journal of Experimental Agriculture 43, 1-18. Demiriz H (1970) Dorycnium Miller. In 'Flora of Turkey and East Aegean Islands'. (Ed. PH Davis) pp. 512-518. (Edinburgh University Press: Edinburgh) DISMED (2003) Climate quality index. Applied Meteorology Foundation. Available: http://dataservice.eionet.eu.int/dataservice ESRI (2000) ArcView GIS v. 8 Environmental Systems Research Institute, Inc., Redlands, California, USA. GBIF Data Portal (2005) Available: www.gbif.net Greuter W, Burdet H, Long G (Eds) (1989) 'Med-Checklist Volume 4.' (Conservatoire et Jardin Botaniques de la Ville de Genève: Genève) Hill MJ (1996) Potential adaptation zones for temperate pasture species as constrained by climate: a knowledge-based logical modelling approach. Australian Journal of Agricultural Research 47, 1095-1117. Hutchinson MF, McIntyre S, Hobbs RJ, Stein JL, Garnett S, Kinloch J (2005) Integrating a global agro-climatic classification with bioregional boundaries in Australia. Global Ecology and Biogeography 14, 197-212. Meikle RD (Ed.) (1977) 'Dorycnium Mill.' The Flora of Cyprus. Vol. 1 (Bentham-Moxon Trust, Royal Botanic Gardens: Kew, London) National Land and Water Resources Audit Metadata. (2001) CSIRO Land and Water. Available: http://www.nlwra.gov.au/ Post GE, Dinsmore JE (Eds) (1933) 'Flora of Syria, Palestine and Sinai.' (American Press: Beirut, Lebanon) Pottier-Alapetite G (Ed.) (1979) 'Flore de la Tunisie.' (Officielle de la Republique Tunisie) Sutherst RW, Maywald GF (1999) CLIMEX: Predicting the effects of climate on plants and animals. CSIRO Publishing, Collingwood, Victoria, Australia. Townsend CC (Ed.) (1974) 'Dorycnium Mill.' Flora of Iraq. Vol. 3 (Ministry of Agriculture and Agrarian Reform of the Republic of Iraq: Bagdad)


Zohary M (Ed.) (1972) 'Flora Palaestina.' (Israel Academy of Sciences and Humanities: Jerusalem, Israel)

Chapter 4: Comparative water use by Dorycnium hirsutum-,

lucerne- and annual-based pastures in the Western

Australian wheatbelt

Abstract

Dryland salinity in southern Australia has been caused by inadequate water use by

annual crops and pastures. The purpose of this study was to compare the water use of

annual pastures and Medicago sativa L. (lucerne) to Dorycnium hirsutum (L.) Ser., a

potential new perennial forage species. The soil water dynamics under bare ground,

annual legume-, lucerne- and D. hirsutum-based pastures were compared at two sites in

the low (Merredin) and medium (New Norcia) rainfall wheatbelt of Western Australia

between September 2002 and February 2005.

Soil under D. hirsutum was drier than annual pastures by 8–23 mm more in year 1, 43–

57 mm in year 2 and 81 mm in year 3. Lucerne used little additional water (< 19 mm)

compared to D. hirsutum and both species displayed similar total soil water contents

throughout the experiment. At Merredin, annual pastures only used water from the top

1.0 m of the soil profile, while under both D. hirsutum and lucerne in the first three

years after establishment the maximum depth of water use was 1.0, 1.8 and 2.2 m. At

New Norcia, additional soil water was extracted by lucerne and D. hirsutum at depths <

1.0 m and no difference between treatments was detected below 1.0 m. The comparable

water use of lucerne and D. hirsutum suggests that D. hirsutum could make reductions

in recharge similar to those of lucerne in the Western Australian wheatbelt.

Chapter 4: Water use of Dorycnium hirsutum 82

Introduction

Dryland salinity has developed in Australia due to an hydrological imbalance that

developed when native deep-rooted perennial vegetation was removed and replaced

with shallow-rooted annual crops and pastures (Hatton and Nulsen 1999). Due to the

excess water that leached past the root zone of the annual plants, this change in

vegetation greatly increased the recharge of groundwater tables, causing them to rise

and bring saline groundwater to the surface. To reduce the spread of salinity it is

proposed that deep-rooted perennial plants that increase water use are reintroduced into

agricultural systems (Clarke et al. 1998; Dunin 2002).

Perennial pastures provide one option to increase water use, while maintaining

agricultural production and without developing new industries (Cransberg and

McFarlane 1994; Cocks 2001; Ewing and Dolling 2003). Lucerne (Medicago sativa L.)

has been successfully used to replace annual pastures in cropping systems and has been

shown to use more water than annual pastures (Angus et al. 2001; Latta et al. 2001;

Ridley et al. 2001; Latta et al. 2002). Lucerne is able to do this due to two mechanisms.

First, the deeper root system of lucerne enables it to extract water from greater soil

depths than annual plants and thus lucerne dries a larger volume of the soil. Secondly,

lucerne is able to rapidly use rainfall that occurs outside the growing season of annuals;

rainfall that would otherwise be stored in the soil. Thus a lucerne pasture is able to

establish a larger dry soil ‘buffer’ than under annuals that would need to be refilled

before drainage can occur (Ridley et al. 2001). In Western Australia, lucerne typically

extracts 50 to 100 mm more water from the soil than annual pastures (Latta et al. 2001;

Latta et al. 2002). However, in south-eastern Australia, where lucerne is better adapted,

larger differences have been reported (Angus et al. 2001; Ridley et al. 2001). Dolling et

al. (2005) demonstrate that the size of the soil buffer is much smaller on soils with

poorly structured or acid subsoil due to impedance of the rooting depth of lucerne.

Despite the relatively wide adaptation of lucerne, its suitability to acid and waterlogged

soils and environments where summer rainfall is low is doubtful (Cocks 2001;

Humphries and Auricht 2001). Thus, over a significant area of southern Australia no

viable perennial forage legumes are available. In addition, diversity is needed to reduce

the risk of invasion by exotic pests and diseases. The Dorycnium genus has been

83

identified as containing potential alternative perennial forage legumes that could play a

role in the management of dryland salinity (Bennett 2002; Dear et al. 2003). Dorycnium

are exotic species that originate from the Mediterranean regions of Europe, west Asia

and Africa. They have only recently been domesticated and little is known about their

agronomic characteristics (Chapters 2 and 3).

Few Australian studies have investigated water use in perennial pastures other than

lucerne and none have measured the water use of Dorycnium species. Lolicato (2000)

showed that Phalaris aquatica L. (phalaris) and Lotus corniculatus L. (birdsfoot trefoil)

dried the soil to 2.0 m (maximum depth of measurement), but maximum water

extraction was less than lucerne by 20 mm and 30 mm, respectively. Cocksfoot

(Dactylis glomerata L.) has been shown to be less successful at drying the soil profile

than phalaris and lucerne (Lolicato 2000; Sandral et al. in press) due to a shallower

rooting depth, which enabled drying of the soil profile to only 1.2 m (Lolicato 2000).

Sandral et al (in press), in their multi-species study, also found that Consol lovegrass

(Eragrostis curvula (Schrader) Nees.) and danthonia (Austrodanthonia richardsonii

Cashmore) achieved a similar soil water deficit to lucerne after 3 years, although this

was achieved more slowly than under lucerne.

The purpose of this study was to compare the soil water dynamics in low and medium

rainfall wheatbelt environments under Dorycnium-based pastures with pastures based

on lucerne and the shallow-rooted annual legumes, burr medic (Medicago polymorpha

L.) and subterranean clover (Trifolium subterraneum L.). We hypothesise that

Dorycnium-based pastures will use more water than annual pastures but less than

lucerne. Plant density and biomass production were also measured to assess the

persistence and productivity of Dorycnium compared to lucerne- and annual-based

pastures.


Site description and history

The two experimental sites were located at Merredin Department of Agriculture

Research Station (31º31’S, 118º10’E, 315 mm long-term mean annual rainfall (MAR))

and 10 km north of New Norcia (30º54’S, 116º14’E, 480 mm MAR). Both sites were


located on lower slopes (< 2% gradient) on a yellow sandy earth (Moore 2004), also

known as a yellow kandosol (Isbell 1996). A description of soil texture, colour, pH (1:5

0.01 M CaCl2) and bulk density at depths to 80 cm is provided for both sites in Table 1.

The Merredin site had been in long-term rotation between annual crops and pastures,

with the previous 5 years (i.e. 1997–2001) consisting of wheat followed by volunteer

pasture, canola, wheat and lupins. The New Norcia site had been sown to lucerne the

previous year.

Table 1. Soil properties to a depth of 80 cm at the Merredin and New Norcia sites.

Site Depth (cm)

Texture Colour A pH (CaCl2)

Bulk density (g/cm3)

0–20 Sandy loam 2.5Y 4/4 4.1 ± 0.05 1.80 ± 0.04

20–40 Sandy loam 2.5Y 5/6 4.8 ± 0.15 1.69 ± 0.02

40–60 Sandy clay loam 5YR 5/6 5.6 ± 0.10 1.74 ± 0.08

Merredin

60–80 Clay loam, sandy 5YR 5/6 5.8 ± 0.20 1.71 ± 0.06

0–20 Sandy loam 2.5Y 5/4 4.4 ± 0.20 1.65 ± 0.03

20–40 Sandy loam 2.5Y 6/4 4.3 ± 0.10 1.66 ± 0.03

40–60 Sandy clay loam 2.5Y 6/6 5.0 ± 0.10 1.67 ± 0.02

New Norcia

60–80 Sandy clay loam 2.5Y 6/6 5.3 ± 0.05 1.67 ± 0.02 A Munsell Soil Colour chart

Experimental design

At New Norcia, 4 replicate plots (4.8 × 5 m) of each treatment were established, while

at Merredin 6 replicate plots (2.4 × 4 m) were used. At both sites treatments were

arranged in a randomised block design and between plots 1.2 m wide buffers were sown

to annual pasture. Treatments at both sites consisted of bare ground, lucerne cv Sceptre,

Dorycnium hirsutum (L.) Ser. (accession TAS 1002) and annual pasture; Medicago

polymorpha L. cv. Santiago (burr medic) at Merredin and Trifolium subteranneum L.

cv. Dalkeith (subterranean clover) at New Norcia. Two other accessions of D. hirsutum

(AL 4858 and SA 33716) were sown at New Norcia but data is not presented because

lower plant densities were present in these plots. Three accessions of D. rectum (L.) Ser.

(TAS 135, TAS 1274 and SA 1231), two accessions of Lotus creticus L. (CPI 66507

and S1012) and Lotus maroccanus Ball (SA 12953) were also planted at New Norcia

but failed to establish due to the dry seasonal conditions experienced during 2002 (Fig.

1). Subsequently, on these plots the following year, treatments of bare ground, lucerne

85

cv. Sceptre and D. hirsutum (composite line) were repeated. A second treatment of D.

hirsutum was also sown in 2003 at Merredin on spare plots.

Site preparation and management

Both sites were prepared with two applications of glyphosate (720 g/ha), one following

the break of season and the second approximately one week prior to sowing. Residual

lucerne plants remained at low density (< 1 plant/m2) at New Norcia in 2002 and these

were removed by hand during the establishment year. Grass selective herbicides were

applied after sowing in August 2002 to reduce competition from grasses, mainly annual

ryegrass (Lolium rigidum L.) (sethoxyolim 93 g/ha at New Norcia and trifluralin 480

g/ha at Merredin). Plots were weeded by hand in the establishment year to reduce the

significant weed competition, mostly from capeweed (Arctotheca calendula (L.)

Levyns) and wireweed (Polygonum aviculare L.). In subsequent years after

establishment weeds were not controlled, thus pastures also contained a significant

proportion of volunteer annual legumes, mainly subterranean clover and balansa clover

(Trifolium michelianum Savi) at New Norcia, grasses, mainly annual ryegrass and

barley grass (Hordeum spp.), and broad-leafed weeds, mainly capeweed and mallow

(Malva parviflora L.)).

Pasture treatments were sown on 23 May 2002 at Merredin and 2 July 2002 at New

Norcia. Plots were sown in the second year at New Norcia on 20 August 2003 and at

Merredin on 28 May and 2 July 2003, 3 plots on each date. Lucerne and D. hirsutum

were sown at 7 kg/ha in 2002 and 5 kg/ha in 2003. Seeding rate for subterranean clover

and burr medic was 15 kg/ha. One hundred kg/ha of single superphosphate was applied

to both experimental areas at sowing in 2002.

Plots at both sites were managed in the absence of grazing because of the unknown

grazing management requirements for D. hirsutum and the different cutting

management that was used for the pastures. However, at New Norcia all plots were

inopportunely grazed by cattle for 2 weeks in early March 2004. During the growing

season plots were mechanically mown to approximately 2 cm above ground level at 6–8

week intervals in conjunction with biomass cuts on lucerne and annual pastures. Cut

biomass was left on plots. During summer and autumn, when annual pastures were not

growing, lucerne plots were only cut when approximately > 200 kg DM/ha were


present. To imitate their proposed role as a standing green forage source, D. hirsutum

plots were allowed to accumulate growth and were cut once in early autumn.

Plant density

The persistence of lucerne and D. hirsutum was assessed by measuring plant density in

four permanent 0.5 × 0.5 m quadrats per plot in spring and late autumn during each year

of the experiment.

Biomass production

Dry matter production was not measured during the establishment year. In subsequent

years, biomass was collected from 12 randomly placed 0.5 × 0.5 m quadrats, i.e. 2

quadrats/plot at Merredin and 3 quadrats/plot at New Norcia. Pasture biomass was

measured prior to mowing (described previously) and thus was only measured in

autumn for D. hirsutum. No data were obtained from New Norcia due to low plant

numbers and grazing by cattle in 2004. After biomass was measured plots were mowed

to a height of 2 cm.

The composition of biomass was determined for each quadrat from sub-samples that

were sorted into lucerne/D. hirsutum, annual legumes, grasses and broad-leafed weeds.

The dry mass of sorted sub-samples and unsorted biomass was measured after 3 days in

a 60ºC oven.

Soil water measurements

PVC access tubes (50 mm diameter), sealed at the lower end, were installed at the

centre of each plot prior to sowing in May 2002. A 4:1 kaolin:lime slurry was used to

fill the cavity around the tube. Soil water was measured with a neutron moisture meter

(NMM) (CPN Corp., California) at 20 cm intervals at soil depths from 10 cm to a

maximum depth of 290 cm every 3–4 weeks from September 2002 until February 2005

at Merredin and until December 2004 at New Norcia. New Norcia measurements were

concluded early due to the low numbers of plants remaining.

Neutron moisture meter readings (counts per 16 s) were converted into count ratios by

dividing the count number by a standard count (based on 10 replicates) in the shield

prior to beginning measurements. Count ratios (x) were converted into soil volumetric

water content (SWC) using a linear relationship (Equation 1, a = intercept, b = slope),

87

which was calibrated at soil depths of 10, 30, 50 and 70 cm at each site (Greacen 1981).

The 70 cm calibration was used for measurements at greater depths. The calibration at

each depth was based on a linear regression between count ratio and soil volumetric

water content in four dry plots and four plots watered to field capacity at each site. In

March 2005, when the driest soil profile was expected and after experimental NMM

measurements were completed, soil volumetric water content was calculated from three

replicates of gravimetric soil water content and samples for measurement of soil bulk

density at each depth.

(1) b

axSWC

)( −=

Total profile soil water content (mm) was calculated by adding together the stored soil

water in each depth, as measured by the NMM. For comparisons between treatments

involving the 2002-sown lucerne and D. hirsutum, profile soil water content was

calculated for 0 to 300 cm at Merredin and 0 to 280 cm at New Norcia; NMM readings

at 290 cm in some plots at New Norcia were inconsistent due to their proximity to the

bottom of the tube, and were omitted. For comparisons between 2003-sown lucerne and

D. hirsutum total profile soil water content was calculated from 0 to 200 cm. No change

in soil water content was detected beyond 200 cm in these plots.

Soil water deficit was calculated as the difference between the total soil profile water

content in the vegetated treatments and field capacity, assumed from the maximum total

profile water content measured in bare plots during the experiment. Maximum soil

profile water content was measured at Merredin on 19 August 2003 (310 mm between 0

and 200 cm, and 503 mm between 0 and 300 cm) and at New Norcia on 18 August 2004

(370 mm between 0 and 200 cm and 524 mm between 0 and 280 cm).

Statistical analysis

Total profile soil water content under bare ground, annual pastures, lucerne- and D.

hirsutum-based pastures were analysed for differences using an analysis of variance for

repeated measurements using Genstat 6 (Genstat 6 Committee 2004). An analysis of

variance was conducted on soil volumetric water content data at each depth and

differences in water extraction between treatments identified by a significant treatment

× date interaction. Least significant differences (P < 0.05) were used for comparisions

of soil volumetric water content. Soil water deficit in February and August was analysed


using analysis of variance and treatment differences determined using Tukey’s multiple

comparisons (P < 0.05) (GenStat 6 Committee 2002).

Results

Environmental conditions

For the experimental period annual total rainfall was 208 mm in 2002, 356 mm in 2003

and 280 mm in 2004 at Merredin (315 mm MAR) and 326 mm in 2002, 540 mm in

2003 and 378 mm in 2004 at New Norcia (480 mm MAR) (Fig. 1). Very dry conditions

were experienced at both sites during winter 2002. Between May and October 2002,

only 93 mm of rain fell at Merredin, the lowest on record for this period. At New

Norcia, rainfall between May and October 2002 was 261 mm, which was in the lowest

12th percentile for this period. These conditions greatly inhibited establishment of the

experimental treatments. However, at Merredin rainfall on 6–7 December (16 mm), 28

December (28 mm) and 17–18 February (49 mm) greatly assisted survival of plants at

this site during the first summer. Subsequent years at both sites were indicative of

average years, with > 70% of rain falling between May and October and typically dry

summers with a high water deficit (Fig. 1). Annual potential evapotranspiration, as

estimated by pan evaporation, was similar at both sites, ranging between 2260 mm and

2390 mm. Over the experimental period, pan evaporation exceeded rainfall at Merredin

in all but one month, June 2004, while at New Norcia rainfall exceeded pan evaporation

in June 2003, August 2003, May 2004 and June 2004.

Plant density

In all cases, plant densities of both lucerne and D. hirsutum declined considerably

during the first summer after establishment (Tables 2 and 3). However, this decline was

less severe at Merredin for D. hirsutum sown in 2003 than 2002. Poor establishment at

New Norcia in 2002 led to low densities (< 3 plants/m2) of D. hirsutum in 2003 and

2004. Plant density was also reduced in the second summer after establishment for both

species, but this reduction was less pronounced than in the first summer. Final plant

densities after the third summer were not determined, as the experiment was terminated

prior to 2005 autumn measurements.

89

Figure 1. Measured monthly rainfall (bars) between January 2002 and March 2005, long-term

mean rainfall (dotted lines) and pan evaporation (solid lines) at (a) Merredin and (b) New

Norcia. Pan evaporation for New Norcia was measured at a nearby weather station at Wongan

Hills (30º51’S, 116º44’E).

Table 2. Plant density (plants/m2) of lucerne and D. hirsutum at Merredin measured in spring

and autumn from 2002 to 2004 (mean ± se) (n=24).

Sown 2002 Sown 2003 Date

Lucerne D. hirsutum D. hirsutum

8 Oct. 2002 44 ± 7 44 ± 7

14 May 2003 33 ± 5 17 ± 3

15 Oct. 2003 34 ± 4 13 ± 2 58 ± 3

12 May 2004 16 ± 3 7 ± 2 41 ± 3

6 Oct 2004 15 ± 3 7 ± 2 36 ± 2

(a) Merredin

0

20

40

60

80

100

120

140

160

180

200

Rai

nfal

l (m

m)

0

50

100

150

200

250

300

350

400

Pan

eva

pora

tion

(mm

)

(b) New Norcia

0

20

40

60

80

100

120

140

160

180

200

Jan.

02

Apr

. 02

Jul.

02

Oct

. 02

Jan.

03

Apr

. 03

Jul.

03

Oct

. 03

Jan.

04

Apr

. 04

Jul.

04

Oct

. 04

Jan.

05

Rai

nfal

l (m

m)

0

50

100

150

200

250

300

350

400

Pan

eva

pora

tion

(mm

)


Table 3. Plant density (plants/m2) of lucerne and D. hirsutum sown in 2002 and 2003 at New

Norcia measured from 2002 to 2004 (mean ± se) (n=16).

Sown 2002 Sown 2003 Date

Lucerne D. hirsutum Lucerne D. hirsutum

29 Oct 2002 85 ± 8 16 ± 4

14 Oct 2003 19 ± 3 3 ± 1 88 ± 7 52 ± 3

2 Jun 2004 13 ± 2 1 ± 0 19 ± 5 11 ± 3

Biomass production

Total biomass harvested in D. hirsutum plots was 15–50% less than from annual pasture

and lucerne at Merredin (Fig. 2). When biomass was measured in February, the annual

component in D. hirsutum plots was minimal and some leaf material had been lost prior

to harvest. Nonetheless, cumulative annual growth of D. hirsutum was less than lucerne,

particularly from plots sown in 2002. Despite the lower biomass harvested from D.

hirsutum plots, green material was present in February when other treatments contained

negligible biomass. Biomass production data for D. hirsutum at New Norcia were not

collected in 2003 because of the very low density of plants that remained in plots sown

in 2002 and in 2004 plots were unintentionally grazed before biomass was measured.

Total biomass production of annual pasture and lucerne in 2003 and 2004 was less at

Merredin (Fig. 2) than at New Norcia (Fig. 3). At both sites lucerne plots produced

more biomass than annual pasture in 2003 but broad-leafed weeds were a major

component of the harvested biomass in both pastures. This was particularly the case in

annual pasture plots at Merredin in 2004, where a false break resulted in death of burr

medic seedlings during a dry period after germination. However, in lucerne plots in

2004, lucerne contributed > 40% to total biomass. At Merredin this was due to

additional lucerne growth (1380 kg DM/ha) before the annual pasture germinated in

2003. However, at both sites in 2004 lucerne growth was limited to the growing season

of the annual pastures and little additional growth was produced by lucerne in the

summer and autumn.

At both sites At New Norcia, volunteer annual legumes and grasses made a significant

contribution to biomass in lucerne plots and lucerne made up < 20% of the total annual

biomass production.

91

Figure 2. Total annual cumulative biomass and the contribution of pasture components to biomass in 2003 and 2004 from annual pasture, lucerne sown in 2002 and D. hirsutum sown in 2002 and 2003 at Merredin. Annual pasture and lucerne plots were sampled at 6–8 week intervals, while D. hirsutum plots were measured once in February. (Mean ± sem for total biomass production (n=12))

0

2000

4000

6000

8000

10000

12000

2003 2004 2003 2004 2004

Annual Lucerne 2002 Lucerne2003

Ann

ual b

iom

ass

prod

uctio

n (k

g D

M/h

a)

Lucerne Annual legumeBroad-leafed weeds Annual grass

Figure 3. Total cumulative annual biomass and the contribution of pasture components to biomass in 2003 and 2004 from annual pasture and lucerne sown in 2002 and 2003 at New Norcia. (Mean ± sem for total biomass production (n=12))

0

500

1000

1500

2000

2500

3000

3500

4000

4500

5000

2003 2004 2003 2004 2003 2004 2004

Annual pasture Lucerne D. hirsutum 2002 D.hirsutum

2003

Ann

ual b

iom

ass

prod

uctio

n (k

g D

M/h

a)

Lucerne Annual legume Broad-leafed weedsD. hirsutum Annual grass

D. hirsutum

2002

D. hirsutum

2003


Soil water dynamics

Lucerne and D. hirsutum sown in 2002

Total soil profile water content was similar under lucerne and D. hirsutum at all times

throughout the experimental period (Fig. 4). In the first year after establishment, soil

water content and the maximum soil water deficit in February 2003 under D. hirsutum

did not differ from that of annual pasture and bare ground (Fig. 4 and Table 4).

However, under lucerne at Merredin the maximum soil water deficit was larger than

under annual pasture by 34 mm (Table 4). In the following winter (August 2003) the

soil profile rewet under all treatments with no difference in total soil water content

evident. In the second and third summers, both lucerne and D. hirsutum extracted

progressively more water from the soil profile. The soil water deficit at Merredin in

February was larger than under annual pastures by 56 and 81 mm for D. hirsutum and

69 and 88 mm for lucerne in 2004 and 2005, respectively (Table 4). At New Norcia, the

maximum soil water deficit was larger than under annual pastures by 23 and 43 mm for

D. hirsutum and 40 and 66 mm for lucerne in 2003 and 2004, respectively. The soil

profiles under both lucerne and D. hirsutum at both sites remained drier than bare

ground in the second winter (August 2004), and were drier than under annual pasture,

although this difference was not statistically significant (Table 4).

Lucerne and D. hirsutum extracted water from similar soil depths throughout the

experiment (Fig. 5) and the drier soil profiles were largely due to their ability to extract

water from greater depth than annual pastures. There was little difference in the water

content under annual pasture and D. hirsutum or lucerne between 20 and 60 cm, but

additional water was extracted between 60 and 100 cm by lucerne at both sites and D.

hirsutum at Merredin (Fig. 5). The maximum depth of water uptake by annual pastures

was 100 cm at Merredin and 120 cm at New Norcia. In the first year after establishment,

when the total soil water content did not differ greatly between treatments, D. hirsutum

and lucerne only used water from the top 100 cm of the soil profile (Fig. 5). However, at

Merredin in the second and third summers lucerne and D. hirsutum extracted water to

depths of 180 cm and 220 cm, respectively (Fig. 5). At New Norcia, no differences in

water content in soil layers deeper than 100 cm was evident between annual pastures,

lucerne and D. hirsutum.

93

(a) Merredin

l.s.d.

300

350

400

450

500

550

Tot

al s

oil w

ater

con

tent

(m

m)

(0-3

00 c

m)

(b) New Norcia

l.s.d.

300

350

400

450

500

550

1 S

ep 0

2

1 N

ov 0

2

1 Ja

n 03

3 M

ar 0

3

3 M

ay 0

3

3 Ju

l 03

2 S

ep 0

3

2 N

ov 0

3

2 Ja

n 04

3 M

ar 0

4

3 M

ay 0

4

3 Ju

l 04

2 S

ep 0

4

2 N

ov 0

4

2 Ja

n 05

4 M

ar 0

5

Tot

al s

oil w

ater

con

tent

(m

m)

(0-2

80 c

m)

Figure 4. Total soil water content under bare ground (●), annual pasture (■), lucerne- (○) and

D. hirsutum-based pasture (□) established in 2002 at (a) Merredin (0–300 cm) and (b) New

Norcia (0–280 cm). Bars represent least significant difference (l.s.d.)(P < 0.05) for the treatment

× date interaction.


Table 4. Soil water deficit at Merredin (0–300 cm) and New Norcia (0–280 cm) measured in

February and August under bare ground, annual pasture, lucerne- and D. hirsutum-based

pastures established in 2002. Within each site at each date numbers with different letters are

significantly different (P< 0.05).

Maximum (February) Minimum (August) Site/Treatment

2003 2004 2005 2003 2004

Merredin

Bare ground 35 a 52 a 64 a 0 a 17 a

Annual pasture 28 a 73 a 73 a 0 a 25 ab

D. hirsutum 41 ab 129 b 154 b 3 a 50 ab

Lucerne 62 b 142 b 161 b 22 a 62 b

New Norcia

Bare ground 96 a 57 a 34 a 0 a

Annual pasture 119 ab 105 ab 50 a 19 ab

D. hirsutum 142 ab 148 bc 75 a 49 b

Lucerne 159 b 171 c 75 a 57 b

Lucerne and D. hirsutum sown in 2003

Similar trends in profile soil water content were obtained for plots sown in 2003 as for

those sown in 2002. Total soil water content was similar under all treatments in the first

year after establishment. In the second summer at Merredin, D. hirsutum continued to

extract water from the profile during summer. The soil water deficit under D. hirsutum

in February was 57 mm larger than under annual pasture, with additional soil water

extracted from 60 cm to a maximum depth of 180 cm. At New Norcia, no difference in

total soil water content and depth of water extraction was observed between annual

pasture, D. hirsutum and lucerne. Soil water measurements were completed in

December 2004 at New Norcia, when treatment differences in soil water content were

not evident at either site.

.

95

Figure 5. Volumetric soil water content (SWC) at 20–60 cm, 60–100 cm, 100–140 cm, 140–180 cm and 180–220 cm under bare ground (●), annual pasture (■), lucerne- (○) and D. hirsutum-based pasture (□) established in 2002 at (a) Merredin and (b) New Norcia. Bars represent the least significant difference (l.s.d.)(P< 0.05) for the treatment × date interaction.

20-60 cm

l.s.d.

60-100 cm

l.s.d.

100-140 cm

l.s.d.

140-180 cm

l.s.d.

180-220 cm

l.s.d.

1 S

ep 0

2

1 N

ov 0

2

1 Ja

n 03

3 M

ar 0

3

3 M

ay 0

3

3 Ju

l 03

2 S

ep 0

3

2 N

ov 0

3

2 Ja

n 04

3 M

ar 0

4

3 M

ay 0

4

3 Ju

l 04

2 S

ep 0

4

2 N

ov 0

4

2 Ja

n 05

4 M

ar 0

5

20-60 cm

l.s.d.

0

0.05

0.1

0.15

0.2

0.25

SW

C (v/

v)

60-100 cm

l.s.d.

0

0.05

0.1

0.15

0.2

0.25

SW

C (v/

v)

100-140 cm

l.s.d.

0

0.05

0.1

0.15

0.2

0.25

SW

C (v/

v)

(d) 140-180 cm

l.s.d.

0

0.05

0.1

0.15

0.2

0.25

SW

C (

v/v)

180-220 cm

l.s.d.

0

0.05

0.1

0.15

0.2

0.25

1 S

ep 0

2

1 N

ov 0

2

1 Ja

n 03

3 M

ar 0

3

3 M

ay 0

3

3 Ju

l 03

2 S

ep 0

3

2 N

ov 0

3

2 Ja

n 04

3 M

ar 0

4

3 M

ay 0

4

3 Ju

l 04

2 S

ep 0

4

2 N

ov 0

4

2 Ja

n 05

4 M

ar 0

5

SW

C (v/

v)

(a) Merredin (b) New Norcia


Discussion

This study has demonstrated that D. hirsutum-based pasture used more water than annual

pasture and was capable of drying the soil profile to a similar extent to lucerne. D. hirsutum

was able to extract water from the same soil layers and reduce the soil water content during

spring and summer in a similar fashion to lucerne. Lucerne water use measured in this study

was consistent with other similar studies in the wheatbelt of Western Australia (Latta et al.

2001; Ward et al. 2001; Latta et al. 2002; Ward et al. 2002). For example, Ward et al (2001)

found that water uptake in the first 3 years after establishment from increasing depths of 1.2,

1.5 and 1.9 m created a dry soil buffer of 50, 60 and 75 mm. The ability of lucerne to produce

a larger dry soil buffer than annual pasture by extracting water from deep in the soil profile

and utilising out of season rainfall has been shown to reduce the amount of water that would

otherwise leak past the root zone of annual plants (Ridley et al. 2001; Ward et al. 2001). The

results of this study suggest that D. hirsutum could be equally effective as lucerne at reducing

drainage in the wheatbelt of Western Australia.

Additional water use by lucerne and D. hirsutum was closely related to extraction of water

from deeper layers in the soil profile. In the present study, the maximum depth of water

extraction under both lucerne and D. hirsutum increased by 3 mm/day in the first 2 years, and

1 mm/day in the third year. These results are consistent with calculations from similar studies

on lucerne in Western Australia, where the maximum depth of water extraction by lucerne

increases on average by 3 mm/day, but ranges between 1.7 and 9.2 mm/day, depending on

soil texture and structural constraints to root growth (Dolling et al. 2005). In addition to

extraction from deep soil layers, fuller depletion of water from shallow layers was also

important, particularly at New Norcia. More complete extraction of water by lucerne from

within the root zone of annual crops and pastures has been observed by others (Holford and

Doyle 1978; Angus et al. 2001; Ridley et al. 2001) and may result from either a greater root

density in this region and/or the ability to extract water at lower soil matric potentials.

The comparable water use by D. hirsutum and lucerne was unexpected for a number of

reasons. D. hirsutum plant density was lower than lucerne at all times at both sites. After the

first summer < 3 plants/m2 were present at the New Norcia site and 12 plants/m2 at the

Merredin site. It could be expected that lower plant densities would be less effective at drying

97

the soil profile. However, Virgona (2003) demonstrated in southern New South Wales that

lucerne plant density did not affect the final soil water content, but lower plant densities were

slower to dry the soil profile. In the present study, the lower densities of D. hirsutum than

lucerne appeared to extract water from the soil at similar rates. It could be that D. hirsutum

plants had larger root systems and were able to more effectively explore the soil, but

differences in cutting management between D. hirsutum and lucerne may have also

contributed. D. hirsutum was allowed to accumulate growth throughout the year until autumn,

to simulate a standing green forage reserve, while lucerne was cut every 6–8 weeks to 2 cm,

when sufficient growth was present. Leaf area duration was not measured in the experiment

and D. hirsutum may have used more water because of greater biomass being present during

summer. Thus a more intensive defoliation regime may lessen or slow water extraction by D.

hirsutum.

The comparable water use of lucerne and D. hirsutum was also unexpected given that D.

hirsutum has only recently been domesticated and have not been actively selected for

improved growth rate and/or deep-rootedness. The origin of the D. hirsutum accession used in

the study is unknown and its suitability to the soil type and climatic environment in this study

is uncertain. The two experimental sites, in particular Merredin, were located in a climatic

region where the adaptation of lucerne is questionable (Hill 1996). Similarly, the low surface

soil pH of both sites is marginal for lucerne. The water use by D. hirsutum in these situations

suggests that there is a large opportunity for well adapted accessions of alternative perennial

legumes to use equivalent or larger amounts of water than current lucerne varieties.

Although D. hirsutum pastures used similar amounts of water to lucerne, less biomass was

harvested from these plots. Undoubtedly the single harvest in autumn under-estimated the

total annual biomass production on D. hirsutum plots because the annual component was not

present and some D. hirsutum leaves had been shed. At New Norcia, the majority of biomass

in plots sown in 2002 was annual species due to the very low density of D. hirsutum. Despite

the lower productivity of D. hirsutum, its ability to maintain some biomass during water stress

ensured that useful amounts of green forage were present during summer and autumn (400–

1200 kg/ha)(Fig. 2), when annuals were dead and lucerne growth was negligible. The

productivity of D. hirsutum-based pasture could be improved significantly in a mixture with

suitable annual species, while even low densities of D. hirsutum could provide water use

benefits and be utilised for forage when other feed sources are in short supply. However, at


New Norcia strong competition from annuals was detrimental to D. hirsutum survival

(Chapter 5). Thus appropriate grazing management to control competition between annual

and perennial pasture components may be needed to ensure D. hirsutum persistence.

Conclusions

This study has shown that D. hirsutum, when managed as a standing green forage reserve, can

use similar amounts of water to lucerne and would presumably reduce deep drainage to a

similar extent. However, DM production from D. hirsutum-based pasture managed in this

way was less than lucerne. D. hirsutum is relatively untried in the wheatbelt of Western

Australia and testing used wild germplasm of questionable suitability to the climatic

conditions. Thus, there appears to be a large opportunity for adapted alternative perennial

legumes in these environments. Selection of appropriate germplasm may improve DM

production, persistence, and possibly water use of D. hirsutum. The possible future role of D.

hirsutum still remains to be resolved but its capacity to use more water than annual pastures

and thus reduce groundwater recharge seems to make it a promising alternative to lucerne.

References

Angus JF, Gault RR, Peoples MB, Stapper M, van Herwaarden AF (2001) Soil water extraction by dryland crops, annual pastures, and lucerne in south-eastern Australia. Australian Journal of Agricultural Research 52, 183-192. Bennett SJ (2002) Distribution and economic importance of perennial Astragalus, Lotus and Dorycnium. In 'New Perennial Legumes for Sustainable Agriculture'. (Ed. SJ Bennett) pp. 90-115. (University of Western Australia Press: Crawley, Western Australia) Clarke CJ, Mauger GW, Bell RW, Hobbs RJ (1998) Computer modelling of the effect of revegetation strategies on salinity in the western wheatbelt of Western Australia 1. The impact of revegetation strategies. Australian Journal of Soil Research 36, 109-129. Cocks PS (2001) Ecology of herbaceous perennial legumes: a review of characteristics that may provide management options for the control of salinity and waterlogging in dryland cropping systems. Australian Journal of Agricultural Research 52, 137-151. Cransberg L, McFarlane DJ (1994) Can perennial pastures provide the basis for a sustainable farming system in southern Australia? New Zealand Journal of Agricultural Research 37, 287-294. Dear BS, Moore GA, Hughes SJ (2003) Adaptation and potential contribution of temperate perennial legumes to the southern Australian wheatbelt: a review. Australian Journal of Experimental Agriculture 43, 1-18.

99

Dolling PJ, Latta RA, Ward PR, Robertson MJ, Asseng S (2005) Soil water extraction and biomass production by lucerne in the south of Western Australia. Australian Journal of Agricultural Research 56, 389-404. Dunin FX (2002) Integrating agroforestry and perennial pastures to mitigate water logging and secondary salinity. Agricultural Water Management 53, 259-270. Ewing MA, Dolling PJ (2003) Herbaceous perennial pasture legumes: Their role and development in southern Australian farming systems to enhance system stability and profitability. In 'New Perennial Legumes for Sustainable Agriculture'. (Ed. SJ Bennett) pp. 3-14. (University of Western Australia Press: Perth, Western Australia) GenStat 6 Committee (2002) GenStat 6th Edition 6.1.0.200. Lawes Agricultural Trust, Rothampstead, UK. Greacen EL (1981) ‘Soil water assessment by neutron method’. (CSIRO Publishing, Melbourne) Hatton TJ, Nulsen RA (1999) Towards acheiving functional ecosystem mimicry with respect to water cycling in southern Australian agriculture. Agroforestry Systems 45, 203-214. Hill MJ (1996) Potential adaptation zones for temperate pasture species as constrained by climate: a knowledge-based logical modelling approach. Australian Journal of Agricultural Research 47, 1095-1117. Holford ICR, Doyle AD (1978) Effect of grazed lucerne on the moisture status of wheat-growing soils. Australian Journal of Experimental Agriculuture and Animal Husbandry 18, 112-117. Humphries AW, Auricht GC (2001) Breeding lucerne for Australia's southern dryland cropping environments. Australian Journal of Agricultural Research 52, 153-169. Isbell RF (1996) 'The Australian Soil Classification.' (CSIRO Publishing: Collingwood, Australia) Latta RA, Blacklow LJ, Cocks PS (2001) Comparative soil water, pasture production, and crop yields in phase farming systems with lucerne and annual pasture in Western Australia. Australian Journal of Agricultural Research 52, 295-303. Latta RA, Cocks PS, Matthews C (2002) Lucerne pastures to sustain agricultural production in southwestern Australia. Agricultural Water Management 53, 99-109. Lolicato SJ (2000) Soil water dynamics and growth of perennial pasture species for dryland salinity control. Australian Journal of Experimental Agriculuture 40, 37-45. Moore GA (2004) 'Soil Guide: A handbook for understanding and managing agricultural soils.' (Department of Agriculture, Western Australia: Perth, Australia)


Ridley AM, Christy B, Dunin FX, Haines PJ, Wilson KF, Ellington A (2001) Lucerne in crop rotations on the Riverine Plains 1. The soil water balance. Australian Journal of Agricultural Research 52, 263-277. Sandral GA, Dear BS, Virgona JM, Swan AD, Orchard BA (in press) Changes in soil water content under annual and perennial based pasture systems in the wheat-belt of southern NSW. Australian Journal of Agricultural Research. Virgona JM (2003) Effect of lucerne density on soil moisture content during summer in southern NSW. In 'Proceedings of 11th Australian Agronomy Conference'. Geelong. (Australian Society of Agronomy) Ward PR, Dunin FX, Micin SF (2001) Water balance of annual and perennial pastures on a duplex soil in a Mediterranean environment. Australian Journal of Agricultural Research 52, 203-209. Ward PR, Dunin FX, Micin SF (2002) Water use and root growth by annual and perennial pastures and subsequent crops in a phase rotation. Agricultural Water Management 53, 83-97.

Chapter 5: Establishment and summer survival of Dorycnium

hirsutum and D. rectum in Mediterranean environments

Abstract

The genus Dorycnium has been identified for its potential use as a forage plant for

southern Australia, but little is known about factors affecting establishment and

survival. This investigation examined some factors affecting the establishment of D.

hirsutum and D. rectum in Mediterranean environments of south-west Western

Australia. The population dynamics of D. hirsutum and D. rectum seedlings were

investigated during the summer drought in 4 environments. The effect of time of sowing

on establishment and survival of D. hirsutum was tested as a management option for

improving establishment of these species.

Poor seedling performance was observed in both Dorycnium species. Less than 20% of

D. rectum plants survived the summer drought at all locations, compared with > 50%

for D. hirsutum seedlings. Poor seedling vigour coupled with weed competition resulted

in low plant numbers at 2 sites. Compared with autumn sowings, populations of D.

hirsutum sown in August and September had lower plant densities before summer due

to poorer seedling emergence. Plant numbers declined during the summer in all plots,

but losses were greatest in those sown in September. In both experiments small D.

hirsutum plants survived in plots where little competition was present. Improvements in

seedling vigour may be possible with plant breeding but establishment methods that

reduce weed competition are valuable. Spring sowing may enable effective weed

control before seeding, but later sowings run the risk of reducing seedling emergence

and survival.

Chapter 5 is previously published in Australian Journal of Experimental Agriculture, 2005, 45,

1245-1254

Chapter 5: Establishment and survival of Dorycnium spp.

102

Introduction

The genus Dorycnium (Mill.) (canary clovers) is made up of perennial legumes that

range in habit from herbs to small shrubs. It consists of 6 species which originate from

central and eastern Europe and the Mediterranean Basin including northern Africa and

western Asia. There are no records of Dorycnium species being sown commercially, but

they have been identified as potentially useful plants in California (Crampton 1946),

New Zealand (Wills 1983) and Australia (Brockwell and Neal-Smith 1966, E. Hall,

pers. comm.). Dorycnium species have been successfully trialed for the dual purposes of

revegetation and forage production in drought-prone and semi-arid areas in New

Zealand (Wills et al. 1989b; Douglas and Foote 1994). In Australia, attention has been

focused on herbaceous perennial pasture plants that may complement lucerne

(Medicago sativa L.) for managing dryland salinity (Cransberg and McFarlane 1994;

Cocks 2001). Dorycnium has been identified as a genus that may contain useful plants

for this purpose (Bennett 2002; Dear et al. 2003). Two species in particular, D. hirsutum

(L.) Ser. (hairy canary clover) and D. rectum (L.) Ser. (erect canary clover) have

performed well in preliminary experiments in Western Australia. However, little is

known about these species; where they might be best adapted, how they should be

managed and how they will fit into the farming systems of southern Australia.

The ease and reliability of perennial pasture establishment is a vital consideration for

new species. The Mediterranean climate in southern Australia, characterised by

summers with high evaporative demand and low, variable rainfall, imposes constraints

on the growth and survival of perennial plants. This is particularly the case in lower

rainfall regions where the growing season is shorter. In addition, the light textured and

infertile soils of south-western Australia have a low water holding capacity making this

environment especially challenging for perennials. The crucial objective is to ensure

sufficient plants survive from sowing through their first summer, the period of greatest

loss (Campbell and Swain 1973), to form the basis of a productive pasture (Campbell et

al. 1987).

Emergence and vegetative seedling growth in Dorycnium species has been observed to

be slow (Douglas and Foote 1994; Bell 2005). These characteristics are likely to

predispose Dorycnium to establishment problems. Dorycnium species are currently still

103

in the early stages of domestication and improvements in seedling vigour are required

through breeding programs. Nonetheless, a better understanding of the characteristics of

these species will enable agronomic practises to be designed to optimise establishment.

The two experiments described in this chapter investigated issues related to the

establishment of Dorycnium species in agricultural regions with a Mediterranean

climate. The first experiment examined the survival of D. hirsutum and D. rectum over

summer in a range of environments across south-west Western Australia. Sites included

a low and high rainfall environment (315 mm and 590 mm mean annual rainfall (MAR),

respectively) and two medium rainfall environments (approx. 480 mm MAR). The

second experiment investigated the influence of sowing time on plant size and ultimate

survival of summer drought in D. hirsutum. Outcomes from these two studies will

provide useful information about the agronomy and management required for successful

establishment of Dorycnium species in Mediterranean environments.


Experiment 1: Species and summer survival

Seed from composite lines of D. hirsutum and D. rectum were sown at a depth of

approximately 10 mm using a knife-point press wheel seeder at four locations spanning

a range of environments in the south-west of Western Australia in the winter of 2002

(see Table 1 for details of site location, soil type, mean annual rainfall, sowing date and

sowing rate). Plot size ranged from 9.6 m2 to 24 m2. Seed germinability after

scarification was 94% for D. hirsutum and 46% for D. rectum. Seed was inoculated with

Rhizobium for Lotus corniculatus, which has been shown to be effective in Dorycnium

(Wills et al. 1989a), in a peat slurry and pelleted with lime. At all sites 100 kg super-

phosphate/ha was applied at sowing. Prior to sowing all sites were sprayed with 2 L/ha

of Roundup® (360 g/L glyphosate) and were treated with a grass selective herbicide

post sowing (500 ml/ha Sertin® (186 g/L sethoxyolim) at New Norcia, Bibby Springs

and Katanning, 1 L/ha Triflurolin® at Merredin). Weeds were also removed by hand,

but residual weeds were present at Merredin and New Norcia following weed control

treatments.

At the end of the first growing season two replicates of 25 randomly selected plants,

were tagged and the length of the longest stem and number of stems were recorded. The


104

status and size of plants were monitored at approximately monthly intervals during the

ensuing summer. Plant densities were determined from plant counts in permanent 0.25

m2 quadrats at each site at various stages over the summer. Plots were not grazed during

the experiment. The rainfall for the experimental period was measured at weather

stations located at nearby Merredin and Katanning Research Stations, and from

collaborating farmers’ rainfall records for Bibby Springs and New Norcia.

Table 1. Site description, sowing date and sowing rate for each experimental site sown in 2002

Sowing rate (kg/ha) Site Location

MAR (mm)A Soil type

Sowing date

D. hirsutum D. rectum

Merredin 31°31′S, 118°10′E

315 Yellow duplex soil

23 May 7.2 6.2

New Norcia 30°54′S, 116°14′E


3 July 7.2 6.2

Katanning 33°42′S, 117°32′E


17 June 5.0 5.0

Bibby Springs 30°20′S, 115°16′E

590 Siliceous sand

4 July — 5.0

ALong-term mean annual rainfall

Experiment 2: Time of sowing

D. hirsutum (accession TAS 1002, courtesy of E. Hall) was sown by hand at 4 different

times over the winter and spring of 2003 at the Merredin site (described in Table 1) in

9.6 m2 plots with 3 replicates. Sowing times (approximately 5 weeks apart) were 28

May, 2 July, 6 August and 10 September 2003, representing late autumn, early winter,

later winter and early spring, respectively. Seed was inoculated with Rhizobium for

Lotus corniculatus (as in experiment 1) the day prior to sowing. Seeds were sown at a

depth of approximately 10 mm. The average seed size was 4.2 mg and the sowing rate

was 5.0 kg/ha (i.e. 120 seeds/m2). Plots were maintained weed free during the

experiment by applications of approximately 2 L/ha of Roundup® (360 g/L glyphosate)

when weeds emerged prior to sowing and hand weeding after sowing. Initial plant

density was measured 5 weeks after sowing in 4 permanent 0.25 m2 quadrats per plot

and subsequently measured at various stages during the following summer until the first

rains in April 2004. In addition, 20 randomly selected plants/ plot were tagged and the

length of the longest stem and number of terminal stems recorded monthly.

105

Water relations of plants sown in May, June and August were monitored during the

ensuing summer by measurements of soil water content, leaf water content, stem water

potential and leaf osmotic potential. Plants sown in September were not measured as

they were too small. Stem water potential at midday (between 11 am and 2 pm), the

peak time of plant stress was measured in a pressure chamber measurements on the

primary stem of 6 average sized plants from each treatment. After stem water potential

was measured, samples were snap frozen on dry ice and stored at -20ºC. The sap from

each sample was expressed using a leaf press and its osmolarity measured on a freezing

point osmometer (Fiske Associates, Massachusetts). Osmotic potential (π) of samples

was determined using equation 1. As samples thawed, the youngest fully expanded leaf

from each stem was removed, weighed, dried for 2 days in a 60ºC oven and again

weighed. Leaf water content was then calculated.

(1) 1000

447.2 osmolarity× = π

Soil water was measured to a depth of 2 m with a neutron moisture meter (CPN Corp.,

California). After the experiment was completed neutron moisture meter counts were

calibrated against soil moisture content in four dry plots and four plots watered to field

capacity. Three replicate soil samples were taken at 0–20, 20–40, 40–60 and 60–80 cm

in each plot and the gravimetric soil water content determined. Bulk density was

sampled in one plot at 10, 30, 50 and 70 cm depths in order for volumetric soil water

content to be calculated. The linear calibration developed at 60–80 cm was used for

depths > 80 cm.


The pattern of survival of different plant sizes was analyzed using contingency tables to

carry out Chi Square tests. Other data were subjected to a two-way analysis of variance

in Genstat 6.1 (GenStat 6 Committee, 2002). Normality was checked and all scored

variables found to be normal apart from plant density values, which were square root

transformed prior to analysis. Tukey’s multiple comparisons were used to identify

differences between factors (GenStat 6 Committee 2002).


106

Results

Experiment 1: Species and summer survival

Rainfall

Rainfall during the winter establishment period was below average at all sites (Fig. 1).

This was particularly the case at Merredin, where rainfall between May and October

2002 was in decile 1 of historical records. Little summer rain fell except at Merredin,

where significant rain fell on 6–7 December (16 mm), 28 December (28 mm) and 17–18

February (49 mm). There was negligible rainfall at Bibby Springs between 23

September 2002 and 30 March 2003, when 44 mm fell (Fig. 1).

(a) Merredin

0

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Figure 1. Monthly measured rainfall during 2002–2003 (bars) and long-term mean (dotted line)

rainfall (mm) measured at (a) Merredin, (b) New Norcia, (c) Katanning and (d) Bibby Springs.

Initial populations

At all sites, germination was uneven within plots, with some bare areas and other areas

containing high plant numbers. Plant density and size of initial populations differed

considerably between sites (Table 2 and 3). D. hirsutum established well at all sites and

D. rectum at Bibby Springs and Katanning. Within each site differences between

species in plant density were observed (Table 2); however, differences in plant size

were not large (Table 3). Plants died at Merredin and New Norcia before the start of the

107

measuring period due to weed competition, mainly from capeweed (Arctotheca

calendula Levyns), and dry conditions during winter and early spring.

Table 2. Plant density (plants/m2) before (October–December 2002) and after (May–June 2003)

summer for D. hirsutum and D. rectum at each site (mean ± sem) (n = number of observations).

D. hirsutum D. rectum Site

Oct.–Dec. May–June %

Loss Oct.–Dec.

May–June

% Loss

Merredin (n = 24) 43.6 ± 7.2 12.6 ± 2.3 71 7.2 ± 2.8 0.0 100

New Norcia (n = 16) 16.2 ± 3.7 3.0 ± 0.9 82 1.2 ± 0.6 0.0 100

Katanning (n = 8) 23.6 ± 2.2 17.0 ± 3.5 28 55.5 ± 6.8 7.4 ± 1.6 87

Bibby Springs (n = 8)

— — — 28.8 ± 2.6 3.0 ± 1.1 90

Table 3. Average plant size at the end of the 2002 growing season for D. hirsutum and D.

rectum at each site (mean ± sem) (n = 50).

Longest stem length (cm)

Number of stems/plant Site Date of

measurement D. hirsutum D. rectum D. hirsutum D. rectum

Merredin 7 Nov. 2002 4.0 ± 0.4 2.0 ± 0.2 1.7 ± 0.1 1.4 ± 0.1

New Norcia 25 Nov. 2002 6.6 ± 0.5 6.5 ± 0.3 1.5 ± 0.2 1.7 ± 0.1

Katanning 10 Dec. 2002 12.4 ± 0.8 13.1 ± 0.6 2.3 ± 0.2 2.4 ± 0.2

Bibby Springs 18 Dec. 2002 — 15.4 ± 0.6 — 3.8 ± 0.3

Population survival

A large difference in the proportion of tracked plants that survived the summer was

observed between species (Fig. 2). Over 80% of D. rectum plants died over the summer

at all sites except Katanning, while D. hirsutum survival rate was better (> 50%) at all

sites. Before plant tracking, 30% of the D. rectum plants had already died at Katanning.

The majority of plants died before March at all sites (Fig. 2), after which the remaining

plants generally survived until the end of the scoring period at the break of the season at

the end of April. Plant density declined during the summer at all sites (Table 2),

particularly in quadrats with a higher plant density at the beginning of the summer. The

decline in plant density was greater in D. rectum than D. hirsutum. At Merredin and

New Norcia no D. rectum plants remained after summer. Low numbers of D. rectum

plants remained at Katanning and Bibby Springs.


108

0

10

20

30

40

50

60

70

80

90

100

1 Nov. 02 1 Dec. 02 31 Dec. 02 30 Jan. 03 1 Mar. 03 31 Mar. 03 30 Apr. 03

Pro

port

ion

of p

lant

s al

ive

(%)

Figure 2. Proportion of tracked plants of D. hirsutum (filled symbols) and D. rectum (clear

symbols) surviving from Nov. 2002 to May 2003 in 4 Western Australian environments (�,

Merredin; �, New Norcia; �, Katanning; �, Bibby Springs). Bar represents the standard

deviation of the data.

Plant size effects

Differences in the average plant size were apparent among initial populations at each

site (Table 3), but these differences were not related to the proportion of plants that

survived (Fig. 2). Plants of similar size at different sites did not have the same

probability of surviving the summer (Table 4 and 5). For example, a greater proportion

of D. hirsutum plants with a stem length < 6 cm survived at Merredin than at New

Norcia.

Within some sites a relationship between plant size and survival was apparent. In D.

hirsutum at Merredin and New Norcia, smaller plants had a much lower likelihood of

surviving (Table 4). At both sites plants with a longest stem length > 6 cm had a much

higher chance of survival. However, this trend was not evident at Katanning. In D.

rectum, larger plants had a higher probability of survival at New Norcia and Katanning,

but not at Bibby Springs (Table 5). As all plants died at Merredin, data were not

analysed. In general, it appeared that D. rectum plants with a primary stem length of >

12 cm had a greater chance of survival. All but 1 plant failed to reach this size at New

Norcia and Merredin. At Katanning and Bibby Springs, 46% and 70% of plants,

109

respectively, had a stem length > 12 cm. These plants survived well at Katanning, but at

Bibby Springs plant survival was still low.

Table 4: Survival through the summer of different sized D. hirsutum plants (% of total initial

population) at 3 different sites in south-west Western Australia. Initial populations were

measured in November–December 2002 and final survival determined in May 2003.

New Norcia Merredin Katanning Longest stem

length (cm) Initial Final Initial Final Initial Final

0–3.0 20 0 48 16 4 4

3.1–6.0 30 14 34 28 8 6

6.1–9.0 32 26 16 16 24 22

9.1–12.0 16 16 2 2 20 16

12.1–15.0 2 2 – – 12 10

15.1–18.0 – – – – 18 18

> 18.1 – – – – 14 14

Total 100 58 100 62 100 90

χ2 49.3* 33.7* 5.3 n.s.

*P< 0.01; n.s., not significant.

Table 5. Survival through summer of different sized D. rectum plants (% of total initial

population) at 4 different sites in south-west Western Australia. Initial populations were

measured in November–December 2002 and final survival determined in May 2003.

New Norcia Merredin Katanning Bibby Springs Longest stem length (cm) Initial Final Initial Final Initial Final Initial Final

0–3.0 8 0 92 0 0 0 0 0

3.1–6.0 52 4 8 0 2 0 3 0

6.1–9.0 28 0 – – 22 16 8 0

9.1–12.0 10 2 – – 30 14 19 1

12.1–15.0 2 2 – – 18 8 27 4

15.1–18.0 – – – – 18 14 27 6

> 18.1 – – – – 10 10 16 5

Total 100 8 100 0 100 62 100 16

χ2 28.1* n.a. 17.7* 7.3 n.s.

*P< 0.01; n.s., not significant; n.a. not available.


110

Experiment 2: Time of sowing

Rainfall

At Merredin rainfall conditions during the growing season of 2003 were slightly above

average with 249 mm falling between May and October (Fig. 3). This was followed by

a dry spring and early summer with no daily falls of > 5 mm occurring between 1

October 2003 and 5 January 2004, when 20 mm fell. The next major rainfall event was

23 mm on the 9 April. The total rainfall at Merredin from May 2003 to May 2004 was

close to the long-term average (Fig. 3).

Initial populations

Emergence of seedlings was slow at all sowing times with cotyledons present only after

5 weeks. Plant density did not decline before 15 October in the plots of the 2 earlier

sowing dates. Lower plant density was measured at this time in the later sown plots

(Table 6). However, plots sown in August had the same plant density as those sown in

May when measured the following December and May. Earlier sown seedlings had a

greater initial plant size on 15 October than those sown later (Table 7). Seedlings in the

plots sown last still consisted only of cotyledons at this time. Plants continued to grow

in all plots until 2 December with earlier sown plots still maintaining a size advantage.

0

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Figure 3. Monthly measured rainfall (bars) during 2003–2004 and long-term mean rainfall

(dotted line) at Merredin.

111

Table 6. The effect of date of sowing on mean plant density (plants/m2) of D. hirsutum

measured at 3 times after establishment at Merredin. Means within columns followed by the

same letter are not significantly different (P< 0.05, Tukey’s multiple comparison).

Measurement date Date of sowing

15 Oct. 2003 2 Dec. 2003 12 May 2004

28 May 55.3 a 43.1 ab 33.4 ab

2 July 60.0 a 52.3 a 47.3 a

6 Aug. 38.6 b 35.6 b 23.5 b

10 Sept. 34.7 b 6.7 c 5.6 c

Table 7. Mean plant size on 15 October 2003 and 2 December 2003 of D. hirsutum sown at 4

different dates at Merredin. Means within columns followed by the same letter are not

significantly different (P< 0.05, Tukey’s multiple comparison).

Measurement date

15 Oct. 2003 2 Dec. 2003 Date of sowing

Stem length (cm)

No. of stems Stem length

(cm) No. of stems

28 May 3.9 a 1.6 a 9.0 a 4.61 a

2 July 2.6 b 1.1 b 6.8 b 3.87 a

6 Aug. 1.1 c 1.1 b 3.6 c 2.48 b

10 Sept. —A —A 2.1 c 1.45 b

ASeedlings still cotyledons.

Population survival

All treatments displayed a decline in plant numbers over the summer (Table 6). Plant

density declined over the whole summer by 40% in plots sown on 28 May and 6 August

and by 22% in plots sown on 2 July. However, this was much greater in the plots from

the September sowing time, with a decline in seedling density of 79% between 15

October and 2 December, where most plants still consisted only of cotyledons. After 2

December, despite the differences in average plant size between treatments, a similar

proportion of plants survived the summer (Table 8). Later sown populations had a larger

proportion of plants in smaller size categories (Table 7 and 8), which had higher death

rates. However, larger plants within each treatment survived. The proportion of small

plants that survived the summer was greater in plots where there were fewer larger

plants.


112

Table 8. Survival through the summer of different sized D. hirsutum plants (% of total initial

population) sown on 4 dates at Merredin in 2003. Initial measurements provided are for the 2

December 2003 and final measurements were taken on 22 April 2004.

Date of sowing

28 May 2 July 6 August 10 September Longest stem

length (cm) Initial Final Initial Final Initial Final Initial Final

0–3.0 5 0 12 3 33 19 73 38

3.1–6.0 21 12 30 22 55 41 25 20

6.1–9.0 28 22 29 26 10 9 2 2

9.1–12.0 20 16 19 17 2 0 0 0

12.1–15.0 12 10 8 8 0 0 0 0

15.1–18.0 9 7 2 2 0 0 0 0

> 18.1 5 4 0 0 0 0 0 0

Total 100 71 100 78 100 69 100 60

χ2 10.1 n.s. 13.2* 4.7 n.s. 8.25*

*P< 0.05; n.s., not significant.

Water relations

No difference in soil moisture content was measured between times of sowing and a

similar drying pattern over the spring and summer was observed (Fig. 4). No change in

soil water was detected below 1 m. Time of sowing did not significantly affect plant

water status. However, differences in leaf water content, and stem water and osmotic

potential were found between sampling times over the summer period (Fig. 5). Leaf

water content declined until 14 January when 20 mm of rain fell, resulting in a

subsequent increase. Measurements of osmotic and stem water potential decreased at

the 2 December sampling. Plants maintained this stem water potential throughout the

summer, but osmotic potential was higher at the next samplings (16 December and 14

January) and decreased again in February and March. No evidence of osmotic

adjustment was observed from this data.

113

60

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Figure 4. Mean soil water content to 1 m under D. hirsutum from all sowing time treatments

from August 2003 to May 2004 at Merredin (mean ± se). No differences between the soil water

content was found under plots sown at the 4 times.

20 mm rainfall

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DW

)

Figure 5. Mean stem water potential (�), osmotic potential (�) and leaf water content (�) of

D. hirsutum from all sowing time treatments over the summer of 2003–2004 (mean ± se). No

significant differences between plants sown at different times were found.


114

Discussion

This study has identified differences in establishment success between D. hirsutum and

D. rectum in Mediterranean environments. Seedling emergence was slow and early

vigour poor in both species of Dorycnium, consistent with results of previous studies

(Wills et al. 1989a; Douglas and Foote 1994; Wills and Trainor 2000; Bell 2005). The

adaptation of Dorycnium species to Mediterranean environments and the management

strategies required for the effective establishment of Dorycnium will be discussed.

Species differences

The difference in establishment of D. rectum and D. hirsutum in Mediterranean

environments of Western Australia reflects the differences in suitability of the species to

this climate. The results from this study have identified some limitations of D. rectum to

establish reliably in lower rainfall environments (< 600 mm MAR). In its native

environment, D. rectum is generally found in damp areas or close to water courses

(Demiriz 1970) and is unlikely to be well adapted to water limiting conditions. It would

appear that the seedlings lack a suitable strategy to enable them to withstand long

periods of water deficit. Bell (2005) or Chapter 6 found that in controlled conditions D.

rectum seedlings were much slower to produce roots deep in the soil profile than

lucerne and D. hirsutum. Lower rainfall Mediterranean regions have shorter growing

seasons before water stress occurs than higher rainfall regions. D. rectum seedlings may

not develop a deep root system quickly enough to access sufficient subsoil moisture as

the surface soil dries. D. rectum may be able to establish in medium rainfall

environments (~ 450 mm MAR) under more favourable seasonal conditions and where

soils are able to store substantial water in the surface zone, but would be best suited to

higher rainfall environments (> 600 mm MAR) or regions with a more reliable summer

rainfall. Successful establishment of D. rectum has been achieved in New Zealand under

such conditions (Douglas and Foote 1994).

D. hirsutum was better able to establish seedlings and seedlings displayed a superior

survival rate than D. rectum. D. hirsutum develops a deep root system more quickly

than D. rectum (Bell 2005 or Chapter 6), so can access subsoil moisture during periods

of water stress. Despite this, differences in tolerance of water deficit might also exist. D.

hirsutum displayed good drought tolerance and may be suitable for low to medium

rainfall regions (< 450 mm). The drought tolerance of D. hirsutum has been well

115

documented in New Zealand (Wills 1984; Douglas and Foote 1994; Wills and Trainor

2000).

Survival strategies

The ability of perennials to resist drought is the key to their survival in a Mediterranean

environment. Perennials employ two main strategies. Firstly, they grow roots that access

water deep in the soil profile. Secondly, they reduce water loss by closure of stomata,

leaf drop or dormancy. Lucerne produces deep roots but also reduces relative leaf water

content and stomatal conductance in response to water stress, and prolonged water

stress initiates leaf drop (Irigoyen et al. 1992). No previous studies have investigated the

mechanisms of drought tolerance in Dorycnium.

This study indicates that D. hirsutum seedlings also employ a number of mechanisms of

drought tolerance. The decline in leaf water content and stem water potential during

spring indicates that the plants respond to the onset of water stress by decreasing plant

water status. However, plant water status did not continue to decrease throughout the

summer. D. hirsutum plants appeared to access sufficient soil water for survival during

this period. Soil water content declined by approximately 0.2 mm per day during spring

and summer (Fig. 4), which is similar to that recorded under lucerne (Ward et al. 2001).

D. hirsutum leaves did not senesce during the summer. Further investigations into the

drought tolerance mechanisms in D. hirsutum are in progress.

Plant size effects

To avoid major plant losses over the first summer it is important that plants achieve

adequate size and develop their root system sufficiently to access subsoil water during

this period. In low rainfall Mediterranean environments the ability of plants to reach

sufficient size is limited by the short growing seasons. In the first experiment, larger

plants within each population of D. rectum and D. hirsutum had a higher probability of

surviving the summer. However, small plants did survive the summer at Merredin in

2002/03 after an extremely dry winter, and summer rain at this site may have aided their

survival. Few large plants were present in those plots, which would have minimised

competition for water. Similarly, in the second experiment, small plants survived the

summer in the September sown plots when competition from other plants was low.

However, in earlier sown plots where a higher plant density and larger plants were

present, the survival rate of small plants was reduced. The larger plants in earlier sown


116

plots exhibited similar water relations to smaller plants in the later sown plots,

indicating that water stress developed similarly in all plant sizes. Water relations

between different sized plants in each plot were not examined and may have identified

differences in water stress. It appears that even small seedlings of D. hirsutum can

survive summer provided competition is limited. Nonetheless, larger plants would be

advantageous if competition from weeds was present.

Management implications

Weed management techniques are necessary during early establishment of perennials to

minimise competition (Campbell et al. 1987). Competition from annuals in spring and

dry summer periods are major reasons for plant loss in the first spring and summer.

These effects have accounted for increasing plant losses by 30% to 80% for lucerne

(Martyn and Heard 1982), and 68% for Phalaris aquatica (Horsnell 1985). The poor

early vigour in Dorycnium compared to lucerne (Bell 2005) means that seedlings are

particularly prone to weed competition during establishment. This was evident in the

poor establishment achieved at New Norcia in 2002/03. Grazing has been used in New

Zealand to reduce competition in spring in establishing pastures of white clover

(Trifolium repens) and perennial ryegrass (Lolium perenne) (Cullen 1970). However,

Dorycnium seedlings are not well adapted to grazing and grazing is not recommended

until their second year (Wills 1983). Sowing when weed numbers are low after a crop

rotation may be helpful but the application of herbicides may still be necessary.

Selective herbicides applied after sowing can be used to control some weed species, but

herbicide resistance to common selective herbicides means that their use must be

rationalised. Non-selective herbicides can be used after a mass emergence of weeds at

the ‘break’ of season prior to sowing. However, delays in germination in some weed

species mean that later applications are more effective. A trade-off between minimizing

weed competition and sowing early enough for plants to establish sufficiently to survive

the summer is anticipated. Sowing at a time that optimizes plant size prior to summer,

while reducing weed competition sufficiently will improve establishment of perennial

species. This experiment has shown that sowing in July minimized seedling death

during establishment and had comparable summer survival to the earlier sown (and

larger) plants. Drier soil surface conditions reduced germination and emergence of seeds

sown at the two subsequent times. This indicates that herbicide application following

the break of the season followed by sowing in early July may be a useful management

option to control weeds and improve establishment of perennial pastures.

117

The success of most perennial pastures is measured by the density of plants achieved

during establishment. Plant densities after establishment in the dry seasonal conditions

of 2002, and at Merredin in 2003 were slightly lower than typical densities of lucerne

after establishment in similar situations i.e. 35–56 plants/m2 (Latta et al. 2001; Ridley et

al. 2001; Latta et al. 2002). However, the purpose of Dorycnium pastures is not solely

to satisfy productivity objectives. High plant densities may not be needed to increase

water use and manage dryland salinity in these environments. Virgona (2003) found that

lucerne pastures of 12 plants/m2 achieved maximum water extraction in a 570 mm

rainfall environment in southern New South Wales. In Chapter 4, D. hirsutum densities

of < 15 plants/m2 also effectively increased water use in the Western Australian

wheatbelt.

Conclusions

The low seedling vigour observed in D. hirsutum and D. rectum is likely to be a major

limitation to their successful establishment and integration into farming systems. D.

rectum appears to be susceptible to summer drought and survival is poor in drought-

prone environments. D. hirsutum, on the other hand, shows good tolerance to summer

drought providing competition from other plants is limited. As there has been little

breeding for cultivar development it is likely that improvements in seedling vigour can

be made through breeding in Dorycnium. However, reliable establishment techniques

need to be further investigated for these species before they can be successfully and

reliably integrated into current farming systems.

References

Bell LW (2005) Relative growth rate, resource allocation and root morphology in the perennial legumes, Medicago sativa, Dorycnium rectum and D. hirsutum grown under controlled conditions. Plant and Soil 270, 199-211. Bennett SJ (2002) Distribution and economic importance of perennial Astragalus, Lotus and Dorycnium. In 'New Perennial Legumes for Sustainable Agriculture'. (Ed. SJ Bennett) pp. 90-115. (University of Western Australia Press: Crawley, Western Australia) Brockwell J, Neal-Smith CA (1966) 'Effective nodulation of hairy canary clover, Dorycnium hirsutum (L.) Ser. in DC.' CSIRO Division of Plant Industry Field Station Record, 5 (1).


118

Campbell MH, Hosking WJ, Nicholas DA, Higgs ED, Read JW (1987) Establishment of perennial pastures. In 'Temperate Pastures: their production, use and management'. (Eds JL Wheeler, CJ Pearson, GE Robards) pp. 59-74. (Australian Wool Corporation/CSIRO) Campbell MH, Swain FG (1973) Factors causing losses during the establishment of surface-sown pasture species. Journal of Range Management 26, 355-359. Cocks PS (2001) Ecology of herbaceous perennial legumes: a review of characteristics that may provide management options for the control of salinity and waterlogging in dryland cropping systems. Australian Journal of Agricultural Research 52, 137-151. Crampton B (1946) Hairy canary clover. Californian Agriculture 18, 12-13. Cransberg L, McFarlane DJ (1994) Can perennial pastures provide the basis for a sustainable farming system in southern Australia? New Zealand Journal of Agricultural Research 37, 287-294. Cullen NA (1970) The effect of grazing, time of sowing, fertilizer and paraquat on the germination and survival of oversown grasses and clovers. In 'Proceedings of the XI International Grasslands Congress'. Surfers Paradise, Australia. (Ed. MJT Norman) pp. 112-115. (University of Queensland Press: St Lucia, Qld.) Dear BS, Moore GA, Hughes SJ (2003) Adaptation and potential contribution of temperate perennial legumes to the southern Australian wheatbelt: a review. Australian Journal of Experimental Agriculture 43, 1-18. Demiriz H (1970) Dorycnium Miller. In 'Flora of Turkey and East Aegean Islands'. (Ed. PH Davis) pp. 512-518. (Edinburgh University Press: Edinburgh) Douglas GB, Foote AG (1994) Establishment of perennial species useful for soil conservation and as forages. New Zealand Journal of Agricultural Research 37, 1-9. GenStat 6 Committee (2002) GenStat 6th Edition 6.1.0.200. Lawes Agricultural Trust, Rothamsted, UK. Horsnell L, J. (1985) The growth of improved pastures on acid soils. 1. The effect of superphosphate and lime on soil pH and the establishment and growth of phalaris and lucerne. Australian Journal of Experimental Agriculture 25, 149-156. Irigoyen JJ, Emerich DW, Sanchez-Diaz M (1992) Alfalfa leaf senescence induced by drought stress: photosynthesis, hydrogen peroxide metabolism, lipid peroxidation and ethylene evolution. Physiologia Plantarum 84, 67-72. Latta RA, Blacklow LJ, Cocks PS (2001) Comparative soil water, pasture production, and crop yields in phase farming systems with lucerne and annual pasture in Western Australia. Australian Journal of Agricultural Research 52, 295-303. Latta RA, Cocks PS, Matthews C (2002) Lucerne pastures to sustain agricultural production in southwestern Australia. Agricultural Water Management 53, 99-109.

119

Martyn RS, Heard AR (1982) Plant density decline of dryland lucerne during establishment. In 'Proceedings of the 2nd Australian Agronomy Conference'. Wagga Wagga pp. 176-179. (Australian Society of Agronomy) Ridley AM, Christy B, Dunin FX, Haines PJ, Wilson KF, Ellington A (2001) Lucerne in crop rotations on the Riverine Plains 1. The soil water balance. Australian Journal of Agricultural Research 52, 263-277. Virgona JM (2003) Effect of lucerne density on soil moisture content during summer in southern NSW. In 'Proceedings of 11th Australian Agronomy Conference'. Geelong. (Australian Society of Agronomy) Ward PR, Dunin FX, Micin SF (2001) Water balance of annual and perennial pastures on a duplex soil in a Mediterranean environment. Australian Journal of Agricultural Research 52, 203-209. Wills BJ (1983) 'Forage plants for the semi-arid high country and rangelands of New Zealand.' Centre of Resource Management, Lincoln College, Special Publication 26, Canterbury, New Zealand. Wills BJ (1984) Alternative plant species for revegetation and soil conservation in the tussock grasslands of New Zealand. Tussock Grasslands and Mountain Lands Institute Review 42, 49-58. Wills BJ, Begg JSC, Foote AG (1989a) Dorycnium species - Two new legumes with potential for dryland pasture rejuvenation and resource conservation in New Zealand. Proceedings of the New Zealand Grassland Association 50, 169-174. Wills BJ, Begg JSC, Sheppard JSS (1989b) Dorycnium and other Mediterranean species - their use for forage and soil conservation in semi-arid environments in New Zealand. In 'Proceedings of XVI International Grassland Congress'. Nice, France p. 1517. (Association Francaise pour la Production Fourragere, Centre National de Recherche Agronomique, Versailles, France) Wills BJ, Trainor KD (2000) Successful drilling of forage species during severe drought in Central Otago - a preliminary report 1998/99. Proceedings of the New Zealand Grassland Association 62, 207-211.

Chapter 6: Relative growth rate, resource allocation and root

morphology in the perennial legumes, Medicago sativa,

Dorycnium rectum and D. hirsutum grown under

controlled conditions

Abstract

Perennial pastures are needed in farming systems in southern Australia to combat

environmental problems such as dryland salinity. The Mediterranean climate in

southern Australia imposes constraints to the growth and survival of perennial plants.

The aim of this study was to compare growth rates, resource allocation and root

distribution in three perennial legumes, Medicago sativa L., Dorycnium hirsutum (L.)

Ser., and Dorycnium rectum (L.) Ser. to assess different plant traits and their ecological

and agronomic significance. Plants were grown in 1-m deep split tubes and destructive

harvests were made every 2 weeks after plant emergence for 10 weeks. Leaf area and

leaf, stem and root fresh and dry weights were measured. Maximum root depth and the

root distribution were also determined.

Seedlings of Dorycnium were slower to emerge and had a lower relative growth rate

(RGR) than M. sativa. The slower RGR was associated with a lower specific leaf area

(SLA) in D. hirsutum and a lower net assimilation rate (NAR) in D. rectum. Although

all species allocated a similar proportion of biomass to roots, D. rectum had a shallower

root distribution and took longer to produce deep roots. The slow growth rates of

Dorycnium seedlings suggest that they are more prone to establishment problems due to

competition from weeds or other pastures, and because they have less access to water at

greater depth during summer drought. However, D. hirsutum displayed characteristics

of a plant that is adapted to stressful environments and therefore may be able to grow in

conditions where other perennial legumes cannot.

Chapter 6 is previously published in Plant and Soil, 2005, 270, 199-211.

Chapter 6: Comparing growth and root morphology of perennial legumes

122

Introduction

Dryland salinity is a major environmental problem in southern Australia. The

replacement of native vegetation with annual crops and pastures has upset the water

balance and resulted in rising groundwater tables that bring salt to the surface. By using

perennial pastures in the farming systems of southern Australia we can combat dryland

salinity by reducing recharge of groundwater, whilst maintaining productivity

(Cransberg and McFarlane 1994; Cocks 2001; Ewing and Dolling 2003). Medicago

sativa (lucerne, alfalfa) is currently the main perennial legume grown in southern

Australia. However, new species are needed to provide diversity and options for regions

where M. sativa is not well adapted, for example, acid soils, waterlogged soils, low

summer rainfall (Humphries and Auricht 2001). Three species of Dorycnium have been

trialed in preliminary field evaluation in Western Australia; D. hirsutum (hairy canary

clover), D. rectum (erect canary clover) and D. pentaphyllum (prostrate canary clover,

scarrillo). D. hirsutum (hairy canary clover) and D. rectum (erect canary clover)

performed productively and are now subject to further investigation (Dear et al. 2003).

The species originate from the Mediterranean. D. hirsutum is widely distributed in

Northern Africa, the Middle East and the Mediterranean regions of Europe as far west

as Portugal. D. rectum is also widely distributed in similar regions, but it is generally

found in damp areas. Both Dorycnium species are frequently referred to as sub-shrubs

and differ from M. sativa because they accumulate woody material. D. hirsutum is a

hairy low growing perennial shrub, while D. rectum is erect (growing to 2 m tall) and

shoots annually from a perennial root stock in a similar way to M. sativa.

Field trials in New Zealand and the wheat-belt of Western Australia have shown that

Dorycnium species are particularly slow growing during establishment from seed

(Sheppard and Douglas 1984; Wills 1984; Chapter 5). Plant traits affecting growth of

Dorycnium species have not been studied to identify the causes of their slow growth.

The absolute growth rate of a plant is a function of its size and its relative growth rate,

the rate of increase in plant weight per unit plant weight. The relative growth rate

(RGR) is determined by two factors, the leaf area ratio and the net assimilation rate

(equation 1) (Evans 1972). Leaf area ratio (LAR) is the amount of leaf area per unit

total plant weight. Net assimilation rate (NAR) is defined as the rate of increase in plant

weight per unit leaf area. LAR is the product of the specific leaf area (SLA), the amount

123

of leaf area per unit leaf weight, and the leaf weight ratio (LWR), the fraction of the

total plant biomass allocated to leaves (equation 2). NAR is predominantly the net

balance of plant photosynthesis and total plant respiration.

(1) RGR = NAR × LAR

(2) LAR = SLA × LWR

These growth parameters are by no means independent, with one factor likely to affect

others. Even though all growth factors affect RGR, SLA is usually the main factor

correlating with variation in RGR (Poorter and Van der Werf 1998). By investigating

the components of growth in Dorycnium species and M. sativa, insight into how these

plants function and reasons for their different growth rates can be explored.

In Mediterranean climates perennial plants must be able to survive summer drought.

This is particularly important in the year of establishment when young plants are still

vulnerable. Differences in plant survival over the first summer have been observed

between M. sativa, D. hirsutum and D. rectum which may indicate differences in their

ability to avoid or tolerate drought (Chapter 5). Although many factors can be involved

in conferring drought tolerance, drought-resistant plants are often characterised by deep

roots (Taylor and Keppler 1978). These plants are likely to allocate more resources to

roots than those from wetter environments. However, there is a trade-off between

greater resource allocation to root growth and faster RGR. Differences in summer

survival between Dorycnium and M. sativa might be due to differences in resource

allocation, growth and root morphology. The aim of this experiment was to test these

characteristics in M. sativa, D. rectum and D. hirsutum by a classical growth analysis to

identify different plant traits and their ecological and agronomic significance.


Experimental design

The experiment was conducted in the glasshouses at the University of Western

Australia, Perth, Australia (31º59´S, 115º53É). Plants were grown in PVC tubes 100

cm deep and 15 cm diameter, cut in half lengthways and reassembled with plastic

adhesive tape and cable ties. The bottom of the tubes was sealed with a plastic base with


124

holes to allow drainage. Five hundred grams of gravel was placed in the bottom of each

tube to a depth of 2 cm. The tubes were filled with an oven-dried and sieved (2 mm)

coarse brown sand (Uc 4.22; Northcote 1971) collected from a site near Lancelin

(31º01’S, 115º20’E), Western Australia. The Lancelin sand has a pH of 5.2 (1:5

soil:0.01M CaCl2 w/v), 8.6 g kg-1 organic carbon, 2 mg kg-1 NO3-, 7 mg kg-1 NH4

+, 2

mg kg-1 P and 46 mg kg-1 K (Qifu et al. 2002). Basal nutrients sufficient for plant

growth (14 mg kg-1 MgCl2, 133 mg kg-1 Ca(H2PO4); 200 mg kg-1 K2SO4; 10 mg kg-1

MnSO4; 10 mg kg-1 ZnSO4; 2mg kg-1 CuSO4; 67µg kg-1 H3BO3; 33µg kg-1 CoSO4 and

17µg kg-1 Na2MoO4) were added to 3 kg of dried soil, which was placed in the top 10

cm of the tubes. Tubes were watered to field capacity and 6 pre-germinated seeds of M.

sativa L. (cv. Sceptre), D. hirsutum (L.) Ser. (accession TAS 1002) and D. rectum (L.)

Ser. (accession TAS 1274) were sown at a depth of 0.5 cm on 15 July 2003. Pre-

germination of scarified seed took place for four days for Dorycnium and one day for M.

sativa prior to sowing, and seeds with similar radicle length (5 mm) were used.

Accessions used were chosen because they previously performed well in field

conditions in Western Australia. Appropriate Rhizobium, group AL for M. sativa and

WSM 1293 for Dorycnium (same as Lotus corniculatus L.) were irrigated onto the soil

surface three days after sowing (DAS). Four replicated tubes for each species were

allocated randomly for the 5 harvests. Tubes were arranged on two glasshouse benches

in a blocked split-plot design to allow for ease of harvesting. Seedlings were thinned to

2 plants per tube after the emergence of the first true leaf, at 14 DAS in M. sativa and at

20 DAS in Dorycnium. Symptoms of nitrogen deficiency were observed in D. rectum at

27 DAS; thus 1 mg NH4NO3 was applied to the surface of each tube every 7 days

thereafter. Plants were watered 3 times a week throughout the experiment.

Sampling procedure and measurements

Harvests were conducted fortnightly after the first harvest at 27 DAS. At each harvest,

shoots were removed, placed in sealed plastic bags and in the laboratory leaves and

stems were separated and fresh weights measured. Leaf area was determined by sub-

sampling and measurement using a portable area meter (LI-3000, LiCor, USA).

Samples were oven-dried for 2 days at 60ºC and dry weights measured. Dry matter

content was calculated from dry and fresh weights and leaf thickness estimated from

fresh weight per unit leaf area (assuming leaf density of 1 g FW/cm3). Tubes were split

and the soil column was sectioned into the following depths, 0–10 cm, 10–20 cm, 20–40

cm, 40–60 cm, 60–80 cm and 80–100 cm. The depth of the deepest root was measured.

125

Soil was washed away from roots over a 2 mm sieve and roots from each section kept

separate, placed in sealed plastic bags and refrigerated overnight. Total root length and

average diameter of roots from each sample were determined using a WinRHIZO root

scanner and WinRHIZO v3.9 software (Régent Instruments Inc., Quebec). Fresh

weights were determined and samples oven-dried for 2 days at 60ºC and dry weights

measured.

Experimental conditions

Glasshouse minimum (4–16 ºC) and maximum (22–35 ºC) daily air temperatures

averaged 11 ºC and 28 ºC, respectively, during the experiment (Fig. 1). Temperatures

increased during the growing period. Minimum (36–64%) and maximum (67–84%)

daily relative humidity averaged 49% and 75%, respectively. Light levels increased

during the growing period but were variable with some cloudy days experienced.

27 DAS 41 DAS 55 DAS 69 DAS 83 DAS

0

5

10

15

20

25

30

35

40

15 Jul 03 29 Jul 03 12 Aug 03 26 Aug 03 9 Sep 03 23 Sep 03 7 Oct 03

Air

tem

per

atu

re (

oC

)

Figure 1. Maximum (●) and minimum (○) air temperature during the experiment. Vertical lines

indicate harvest dates.


Data were subjected to a two-way analysis of variance in Genstat 6 (Genstat 6

Committee 2002). Block effects were not significant. Mean RGR and their standard

errors were calculated using the method outlined by Venus and Causton (1979). Species

× time interaction of the natural log of plant biomass was used to identify significant

differences in RGR. Mean net assimilation rates (NAR) and their standard errors were

calculated by the method of random pairing (Elias and Causton 1975). All other


126

parameters were point measurements and normal standard errors were calculated. Plant

growth data were plotted against a function of plant biomass to remove size effects and

better depict intrinsic differences between species.

Results

Growth factors

Average seed size of the three species was 4.8 mg for D. hirsutum, 2.5 mg for M. sativa

and 1.3 mg for D. rectum. Medicago sativa seedlings emerged at 3 DAS while

Dorycnium species had not fully emerged until 10 DAS, despite the fact that Dorycnium

seeds were pre-germinated 3 days longer than M. sativa and were at a similar stage of

radicle emergence at sowing. At all harvests, M. sativa plants had a higher total biomass

than the Dorycnium species (Fig. 2) and the absolute growth rate of M. sativa plants was

faster than that of the Dorycnium plants. D. rectum plants were 57% the size of (14 mg

smaller) D. hirsutum at the first harvest (27 DAS), the same size at the second harvest

(41 DAS) and achieved a greater biomass subsequently. All species displayed

exponential growth during the period of the experiment, and their growth was described

by logistic curves (Fig. 2).

0

2

4

6

8

10

12

14

16

18

25 35 45 55 65 75 85

DAS

Pla

nt

d. w

t (g

)

Figure 2. Plant growth of M. sativa (●), D. rectum (○) and D. hirsutum (□) seedlings. Growth is

described by the following logistic relationships: M. sativa, y = -0.167 + 53.5/(1 + e-0.1016 × (x -

82.7)); D. hirsutum, y = 0.029 + 4.6/(1 + e-0.116 × (x – 81.0)); and D. rectum, y = 0.012 + 12.6/(1 + e-

0.120 × (x – 85.8)).

127

Relative growth rates for the three species ranged between 60 and 145 mg g-1 day-1 (Fig.

3). Medicago sativa displayed a faster RGR than the Dorycnium species initially, but

RGR declined as plant size increased (Fig. 3). M. sativa had begun flowering by the last

harvest when its RGR was lower than D. rectum. D. rectum displayed a faster RGR than

D. hirsutum initially but no difference was apparent after this. Dorycnium species

maintained a constant RGR during the growing period.

0

20

40

60

80

100

120

140

160

180

3 4 5 6 7 8 9 10

Logex of plant DM (mg)

Rel

ativ

e g

row

th r

ate

(mg

g-1

d-1

)

Figure 3. Relationship between relative growth rate (RGR) and total plant biomass for M. sativa

(●), D. rectum (○) and D. hirsutum (□) (mean ± se).

Differences in net assimilation rate and leaf area ratio between species greatly affected

the relative growth rate. NAR varied between 6.6 and 15.2 g m-2 day-1 for the three

species (Fig. 4). Mean NAR values differed between species over the whole period: M.

sativa, 12.5 g m-2 day-1; D. hirsutum, 10.2 g m-2 day-1; and D. rectum, 8.0 g m-2 day-1.

NAR increased noticeably with plant biomass in all species (Fig. 4). Little difference in

LAR was observed between D. rectum and M. sativa plants of the same size (Fig. 5). D.

hirsutum, on the other hand, began with a much lower leaf area per plant weight than

the other two species. Little difference in LWR was observed amongst plants of the

same size in all three species (Fig. 7a). However, the SLA of D. hirsutum was initially

much lower than that of the other two species (Fig. 6), resulting in a lower LAR (Fig.

5). D. hirsutum leaves had fleshier leaves than the other species and higher dry matter

content than D. rectum (Table 1).


128

0

2

4

6

8

10

12

14

16

18

3 4 5 6 7 8 9 10

Logex of plant d. wt (mg)

Net

ass

imila

tio

n r

ate

(g m

-2 d

-1)

Figure 4. Relationship between net assimilation rate (NAR) and total plant biomass for M.

sativa (●), D. rectum (○) and D. hirsutum (□) (mean ± se).

0

5

10

15

20

25

2 3 4 5 6 7 8 9 10 11


Lea

f ar

ea r

atio

(m

2 kg

-1)

Figure 5. Relationship between leaf area ratio (LAR) and total plant biomass for M. sativa (●),

D. rectum (○) and D. hirsutum (□) (mean ± se).

In M. sativa the decline in RGR (Fig. 3) with increasing plant biomass corresponded

with a decrease in leaf area per plant weight. This was associated with a decrease in

both SLA and LWR. In D. rectum a large increase in LAR was observed initially,

associated with an increase in LWR and SLA. This was followed by a decline in all

three parameters. Increases in plant size in D. hirsutum resulted in a gradual decline in

LAR associated with decreasing SLA.

129

0

5

10

15

20

25

30

35

40

45

50

2 4 6 8 10


Sp

ecif

ic le

af a

rea

(m2

kg-1

)

Figure 6. Relationship between specific leaf area (SLA) and total plant biomass for M. sativa

(●), D. rectum (○) and D. hirsutum (□) (mean ± se).

Table 1. Estimated leaf thickness (mm) and dry matter content (DMC) of M. sativa, D. rectum

and D. hirsutum. Letters denote significant differences (P< 0.01).

Species Leaf thickness (mm) DMC (%)

M. sativa 26 b 18.2 b

D. rectum 28 b 14.8 c

D. hirsutum 37 a 19.5 a

Resource allocation

In general, the species allocated resources similarly to leaves, roots and stems (Fig.

7a,b,c). In all species the proportion of stem increased as plants increased in age. The

proportion of leaf in M. sativa declined steadily over time as stem weights increased.

The leaf weight ratio of D. rectum also declined after the third harvest while in D.

hirsutum it was constant after the second harvest. In both Dorycnium species a

significant increase in the proportion of leaves was observed between the first and

second harvests. This coincided with a reduction in the allocation of resources to roots.

This was not observed in M. sativa. M. sativa plants had a similar root weight ratio to

the Dorycnium species at lower plant biomass, but as plant size increased and

reproductive maturity approached the root weight ratio increased.


130

Figure 7. Resource allocation to (a) leaves (LWR – leaf weight ratio), (b) roots (RWR – root

weight ratio) and (c) stems (SWR - stem weight ratio) in M. sativa (●), D. rectum (○) and D.

hirsutum (□) (mean ± se).

(a)

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7L

eaf

wei

gh

t ra

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(g

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(b)

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Ro

ot

wei

gh

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(c)

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2 4 6 8 10


Ste

m w

eig

ht

rati

o (

g g

-1)

131

Root depth

M. sativa had a faster root depth extension than Dorycnium species, reaching the bottom

of the tubes (1 m) between 41 and 55 DAS (Fig. 8a). D. hirsutum roots reached

maximum tube depth at 69 DAS. D. rectum was slower to produce roots at depth than

the other two species, not reaching the bottom of the tubes until the last harvest (83

DAS). When root depth was compared in relation to plant size little difference was

observed between D. hirsutum and M. sativa (Fig. 8b). On the other hand, D. rectum

plants were much older and larger before deep roots began to develop.

(a)

0

10

20

30

40

50

60

70

80

90

100

25 35 45 55 65 75 85

DAS

Max

imu

m r

oo

t d

epth

(cm

)

(b)

0

10

20

30

40

50

60

70

80

90

100

2 3 4 5 6 7 8 9


Max

imu

m r

oo

t d

epth

(cm

)

Figure 8. Depth of deepest root of M. sativa (●), D. rectum (○) and D. hirsutum (□) as

dependent on (a) plant age and (b) plant size (mean ± se).


132

Root growth and distribution

M. sativa had a much greater total root length than Dorycnium species throughout the

experiment (Fig 9). The specific root length (SRL), length of root per unit weight of

root, varied amongst species and over time (Fig. 10). SRL was initially greatest in M.

sativa (182 m g-1), but declined rapidly during the experiment to 24 m g-1 at 83 DAS

(Fig. 10). This corresponded with an increased tap-root size. The mean SRL for D.

hirsutum and D. rectum over the experimental period was 109 and 89 m g-1,

respectively. Dorycnium species did not exhibit the large decline in SRL seen in M.

sativa and tap-root development was not as pronounced.

0

50

100

150

200

250

300

350

25 35 45 55 65 75 85

DAS

To

tal r

oo

t le

ng

th (

m)

Figure 9. Increase in total root length of M. sativa (●), D. rectum (○) and D. hirsutum (□)

(mean ± se).

M. sativa distributed its roots deeper in the profile earlier than the Dorycnium species

(Fig 11). D. hirsutum had less total root length than D. rectum at 55 DAS (Fig 9), but

had distributed its roots deeper in the soil profile (Fig 11). D. rectum still had > 95% of

its root length distributed in the top 20 cm at 69 DAS. In all species the majority of

roots were distributed in the top 10 cm of the tube with the exception of M. sativa at 83

DAS, which accumulated a large amount of roots at the bottom of the tubes, an artifact

of air pruning.

133

0

50

100

150

200

250

2 4 6 8 10


Sp

ecif

ic r

oo

t le

ng

th (

m g

-1)

Figure 10. Relationship between specific root length (SRL) and total plant biomass for M.

sativa (●), D. rectum (○) and D. hirsutum (□) (mean ± se).

Discussion

Inherent differences in RGR and associated parameters and in root distribution between

M. sativa and Dorycnium were identified in the growth analysis. The factors affecting

differences between these species and the ecological significance of these attributes in

relation to adaptation and integration into farming systems will be discussed.

Growth factors

Both seed size and germination time are important factors affecting absolute growth rate

of plants independent of RGR. Seed size is a major determinant of initial plant size and

absolute growth rate of seedlings (Cooper 1977). In general plants of greater seed size

produce seedlings of greater biomass (Cooper 1977; Fenner 1983). Larger-seeded

species tend to be found in environments where seedlings establish in shade or where

they are prone to drought (Baker 1972). However, plants of smaller seed size frequently

have a faster RGR (Grime and Hunt 1975; Fenner 1983; Gross 1984).


134

(a)

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27 41 55 69 83

% o

f to

tal r

oo

t len

gth

0-10 cm 10-20cm 20-40 cm

40-60 cm 60-80 cm > 80cm

(b)

0.0

0.1

0.2

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27 41 55 69 83DAS

% o

f to

tal r

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t len

gth

(c)

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

27 41 55 69 83DAS

% o

f to

tal r

oo

t len

gth

Figure 11. Distribution of root length in 1-m long tubes containing (a) M. sativa, (b) D. rectum

and (c) D. hirsutum (mean ± se).

135

In this study D. hirsutum possessed the greatest seed size (4.8 mg), and M. sativa (2.5

mg) and D. rectum (1.3 mg) had smaller seeds. D. hirsutum did indeed have a greater

seedling biomass (14 mg) than D. rectum at the first harvest, but was later overtaken

due to the faster RGR of the smaller-seeded D. rectum. Medicago sativa achieved a

greater biomass at the first harvest, largely due to its earlier emergence. Medicago

sativa emerged 7 days prior to both Dorycnium species. During the exponential stage of

plant growth this initial difference resulted in an enormous advantage in plant biomass.

The slow germination of the Dorycnium species is not well understood and slow

emergence is also observed in field conditions (Wills et al. 1989a; Douglas and Foote

1994; Chapter 5). It seems that slow germination and hypocotyl extension is a feature of

Dorycnium species and this is likely to slow their early growth in comparison with M.

sativa in both the glasshouse and field conditions, regardless of any subsequent

differences in growth rates.

In addition to its earlier emergence, M. sativa also displayed a faster RGR than both

Dorycnium species. A number of factors are likely to have resulted in the differences in

RGR between the species. First, the degree of selection for faster growth rate, as traded

off against survival strategies, to which these species have been exposed should be

considered. Cultivars of M. sativa have been bred for faster growth by agriculture for

hundreds of years (Small 2003), and strategies that are associated with survival and

slow growth rate would have been selected against. On the other hand, the Dorycnium

accessions used in this study are not domesticated and have undergone little, if any,

selection for improved growth rate.

Second, differences in adaptations associated with inherent variation in RGR amongst

species should be considered. Fast-growing species generally occur in fertile, productive

habitats where rapid growth is advantageous to compete for resources (Lambers and

Poorter 1992). There is a trade-off between growth potential and adaptation to

unfavourable conditions (Lambers and Poorter 1992). Plants (species or ecotypes) that

occur in adverse conditions like shaded (Grime and Hunt 1975), infertile (Poorter and

Remkes 1990), arid (Rozjin and van der Werf 1986), alpine (Atkin et al. 1996) and

saline environments (Ball 1988), all have lower growth potential than ones from more

favourable environments. In this case M. sativa displayed the fastest growth rate under

favourable conditions. Historically, M. sativa has been grown in moist environments or


136

provided with irrigation and fertilizer, conditions in which M. sativa is highly

productive (Small 2003). Correspondingly, there has been little attempt to cultivate M.

sativa in circumstances of low potential productivity (Small 2003). Therefore, modern

cultivars of M. sativa have originated with a selection pressure for high potential growth

rates in favourable conditions. In comparison, D. hirsutum displayed a slow RGR,

indicative of adaptation to adverse conditions. D. hirsutum is usually found in dry areas

with low fertility, especially on light sandy soils (Allen and Allen 1981). Similarly in

New Zealand its tolerance of frost, high winds and drought has been well documented

(Sheppard and Douglas 1984;1986; Wills et al. 1989b; Wills et al. 2004). Evidence

suggests that D. rectum is less adapted to adverse conditions (Douglas and Foote 1994).

The findings of this experiment are consistent with observations that D. hirsutum is

relatively better adapted to adverse conditions than D. rectum and perhaps even more so

than M. sativa.

The faster RGR of M. sativa was associated with a higher NAR than that of D. rectum

and with a higher SLA than that of D. hirsutum. Variation in SLA most frequently

accounts for differences in RGR (Poorter and Remkes 1990; Poorter and Van der Werf

1998). Variation in SLA can be the result of differences in the number of cells/unit leaf

area, leaf anatomy, morphology and chemical composition. Slow-growing species

reduce leaf turnover and nutrient loss by producing structures and compounds that

increase leaf longevity (Coley et al. 1985). Slow-growing species accumulate more

quantitative secondary compounds (e.g., tannins and lignin) that reduce plant

palatability and herbivory (Coley et al. 1985). In this case both Dorycnium species are

known to accumulate condensed tannins in their leaf material. Exceptionally high

concentrations of 18% in D. hirsutum and 14–20% in D. rectum have been recorded

(Terrill et al. 1992; Waghorn et al. 1998). In addition to the accumulation of secondary

compounds, D. hirsutum produces thick leaves covered in hairs, which reduce

palatability to livestock (Wills et al. 1999). Leaf hairs can also reduce water loss

(Grammatikopoulous and Manetas 1994), protect against radiation damage

(Karabourniotis et al. 1995), decrease leaf temperatures (Ehleringer 1984) and protect

against insect attack (Agren and Schemske 1993). The investment of resources in these

structures and secondary compounds can decrease SLA (Lambers and Poorter 1992)

and results in a low photosynthetic return per unit leaf mass. D. hirsutum also had a

higher fresh weight per leaf area, indicative of thicker leaves than the other species.

137

These characteristics observed in D. hirsutum are again consistent with plants that are

adapted to stressful environments. Despite the high level of secondary compounds

recorded previously in D. rectum a similar SLA was observed to M. sativa. In this study

D. rectum leaves had a lower dry matter content than M. sativa but their fresh mass per

area was similar. This suggests that D. rectum leaves are thinner than the other species.

The slower RGR in D. rectum compared with that of M. sativa was associated with a

slower NAR. A number of factors may have contributed to this but it is likely that

degree of selection for greater growth rate (discussed previously) was a major

contributor.

Ontogenic drift in RGR occurs as plants become larger and more complex (Evans

1972). The accumulation of stem and storage structures means a lower proportion of

plant biomass contributes to photosynthesis. Medicago sativa displayed a greater

decline in RGR throughout this experiment than the Dorycnium species. M. sativa had

begun flowering by 83 DAS and exhibited a shift in its resource allocation from

vegetative growth. Development was more rapid than that of the Dorycnium species,

which rarely flower in their first year. The different ontogeny of M. sativa and

Dorycnium indicates differences in the phenology and development of these species.

Dorycnium being sub-shrubs, compared with the herbaceous M. sativa, may be longer-

lived and therefore ontogenic drift occurs more slowly.

In M. sativa, the reduction in RGR during the experiment was the result of a large

decline in leaf area per plant weight, despite some increase in NAR over the period. The

decreasing LAR resulted from a reduction in SLA and an increase in the proportion of

stem (SWR) and roots (RWR). The increase in RWR as the M. sativa plants matured

probably resulted from allocation of resources for storage in the tap-root which are

utilised to survive drought periods and following defoliation (Avice et al. 1996). In

Dorycnium species RGR was constant. The reduction in LAR after the second harvest

was offset by an increase in NAR. The reduction in leaf area per plant weight was a

result of a small decline in SLA but the proportion of leaves was maintained. Should

this experiment have continued, D. rectum might have displayed a faster RGR than that

of M. sativa plants of the same size.


138

Resource allocation

Resource allocation to roots, leaves and stems was similar in all species. At the first

harvest all species had a higher RWR than was observed at later harvests with the

exception of M. sativa, which increased allocation to roots following 41 DAS

(associated with tap root growth). Plants are particularly vulnerable to drought as young

seedlings, thus more roots are produced at this time. In Dorycnium, nutrient deficiency

at 27 DAS may also have contributed to the higher RWR at this time. In all species,

SWR increased over time with a similar proportion of the DM made up by stems. The

three species allocated resources similarly at the same size demonstrating the

importance of root growth in perennial species. Dorycnium species did not noticeably

increase allocation of resources to roots for storage as they matured, as seen in M.

sativa. M. sativa is well adapted to the growing conditions in this study and is likely to

be more plastic in its allocation of resources than the Dorycnium species. The plants in

this experiment were grown under optimal conditions where they are less likely to

allocate resources to roots than those grown in the field.

Root depth and distribution

While resource allocation to roots is an important factor, the distribution of these roots

in the soil profile indicates the ability of plants to access vital water and nutrients.

Drought resistant perennial plants need deep roots to access sufficient water held deeper

in the profile. The results of this experiment suggest D. rectum seedlings do not produce

roots deep in the soil as early as M. sativa or D. hirsutum. In part this characteristic is

likely to explain the poor survival of seedlings in the field during summer drought in

comparison with D. hirsutum (Chapter 5). This result does not mean that D. rectum does

not produce roots as deep as those of D. hirsutum or M. sativa, but it does mean that in

environments with shorter growing seasons and faster onset of drought after

germination (e.g., the Western Australian wheat-belt) the probability of successful

establishment is reduced. D. hirsutum displayed a similar root morphology and depth to

M. sativa plants of the same size, with plants quickly developing a deep single tap root.

This again indicates that this species is likely to be well adapted to more arid

environments.

139

Conclusions

The growth analysis proved to be a valuable tool for investigating differences in plant

growth characteristics. Slower absolute growth rates in Dorycnium than in M. sativa

were largely correlated with slower emergence and slower RGR during early stages of

seedling growth. D. hirsutum and M. sativa displayed a greater ability to produce roots

at greater depth than D. rectum. This factor may, in part, explain the reason for the poor

drought survival of D. rectum in the field. On the other hand, D. hirsutum displayed

characteristics of a slower-growing species that may be well adapted to harsh

environments that other perennial legumes may not be able to tolerate. Further

investigations on other environmental variables that influence plant survival of

Dorycnium species in the field (e.g. drought tolerance per se) are now underway.

References

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Cransberg L, McFarlane DJ (1994) Can perennial pastures provide the basis for a sustainable farming system in southern Australia? New Zealand Journal of Agricultural Research 37, 287-294. Dear BS, Moore GA, Hughes SJ (2003) Adaptation and potential contribution of temperate perennial legumes to the southern Australian wheatbelt: a review. Australian Journal of Experimental Agriculture 43, 1-18. Douglas GB, Foote AG (1994) Establishment of perennial species useful for soil conservation and as forages. New Zealand Journal of Agricultural Research 37, 1-9. Ehleringer J (1984) Ecology and ecophysiology of leaf pubescence in North American desert plants. In 'Biology and Chemistry of Plant Trichomes'. (Eds E Rodrigues, PL Healey, I Mehta) pp. 113-132. (Plenum: New York) Elias CO, Causton DR (1975) Temperature and the growth of Impatiens parviflora DC. New Phytologist 75, 495-505. Evans GC (1972) 'The Quantitative Analysis of Plant Growth.' (Blackwell Scientific Publications: Oxford, England) Ewing MA, Dolling PJ (2003) Herbaceous perennial pasture legumes: Their role and development in southern Australian farming systems to enhance system stability and profitability. In 'New Perennial Legumes for Sustainable Agriculture'. (Ed. SJ Bennett) pp. 3-14. (University of Western Australia Press: Perth, Western Australia) Fenner M (1983) Relationships between seed weight, ash content and seedling growth in twenty-four species of Compositae. New Phytologist 95, 697-706. Grammatikopoulous G, Manetas Y (1994) Direct absorption of water by hairy leaves of Pholomis fruticosa and its contribution to drought avoidance. Canadian Journal of Botany 72, 1805-1811. Grime JP, Hunt R (1975) Relative growth rate: its range and adaptive significance in a local flora. Journal of Ecology 53, 393-422. Gross KL (1984) Effect of seed size and growth form on seedling establishment on six monocarpic perennial plants. Journal of Ecology 72, 369-387. Humphries AW, Auricht GC (2001) Breeding lucerne for Australia's southern dryland cropping environments. Australian Journal of Agricultural Research 52, 153-169. Karabourniotis G, Kotsabassidis D, Manetas Y (1995) Trichome density and its protective potential against ultra-violet-B radiation damage during leaf development. Canadian Journal of Botany 73, 376-383. Lambers H, Poorter H (1992) Inherent variation in growth rate between higher plants: A search for physiological causes and ecological consequences. Advances in Ecological Research 23, 187-261.

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Poorter H, Remkes C (1990) Leaf area ratio and net assimilation rate of 24 wild species differing in relative growth rate. Oecologia 83, 553-559. Poorter H, Van der Werf DC (1998) Is inherent variation in RGR determined by LAR at low irradiance and by NAR at high irradiance? A review of herbaceous species. In 'Inherent Variation in Plant Growth. Physiological Mechanisms and Ecological Consequences'. (Eds H Lambers, H Poorter, M Van Vuuren) pp. 309-336. (Backhuys Publishers: Leiden) Qifu M, Longnecker N, Atkins C (2002) Varying phosphorus supply and development, growth and seed yield in narrow-leafed lupin. Plant and Soil 239, 79-85. Rozjin NAMG, van der Werf DC (1986) Effect of drought during different stages in the life cycle on the growth and biomass of two Aira species. Journal of Ecology 74, 507-523. Sheppard JS, Douglas GB (1984) Canary clovers. Streamland 32, 4-8. Sheppard JS, Douglas GB (1986) Management and uses of Dorycnium spp. Water & Soil Miscellaneous Publication 94, 260-262. Small E (2003) Distribution of perennial Medicago with particular reference to agronomic potential for semi-arid Mediterranean climate. In 'New Perennial Legumes for Sustainable Agriculture'. (Ed. SJ Bennett) pp. 57-80. (University of Western Australia Press: Perth, Western Australia) Taylor HM, Keppler B (1978) The role of rooting characteristics in the supply of water to plants. Advances in Agronomy 30, 99-128. Terrill TH, Rowan AM, Douglas GD, Barry TN (1992) Determination of extractable and bound condensed tannin concentrations in forage plants, protein concentrate meals and cereal grains. Journal of the Science of Food and Agriculture 58, 321-329. Venus JC, Causton DR (1979) Plant growth analysis: A re-examination of the methods of calculation of relative growth and net assimilation rates without using fitted functions. Annals of Botany 43, 633-638. Waghorn GC, Douglas GB, Niezen JH, McNabb WC, Foote AG (1998) Forages with condensed tannins - their management and nutritive value for ruminants. Proceedings of the New Zealand Grassland Association 60, 89-98. Wills BJ (1984) Alternative plant species for revegetation and soil conservation in the tussock grasslands of New Zealand. Tussock Grasslands and Mountain Lands Institute Review 42, 49-58. Wills BJ, Begg JSC, Foote AG (1989a) Dorycnium species - Two new legumes with potential for dryland pasture rejuvenation and resource conservation in New Zealand. Proceedings of the New Zealand Grassland Association 50, 169-174.


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Wills BJ, Begg JSC, Sheppard JSS (1989b) Dorycnium and other Mediterranean species - their use for forage and soil conservation in semi-arid environments in New Zealand. In 'Proceedings of XVI International Grassland Congress'. Nice, France p. 1517. (Association Francaise pour la Production Fourragere, Centre National de Recherche Agronomique, Versailles, France) Wills BJ, Douglas GB, Foote AG, Trainor KD (1999) Germplasm characterization and palatability of Dorycnium species under New Zealand dryland conditions. Plant Genetic Resources Newsletter 120, 8-14. Wills BJ, Trainor KD, Littlejohn RP (2004) Semiarid land rehabilitation by direct drilling in the South Island, New Zealand - Plant species and establishment technology. Land Degradation and Development 15, 1-14.

Chapter 7: Water relations and adaptations to increasing water

deficit in three perennial legumes, Medicago sativa,

Dorycnium hirsutum and D. rectum

Abstract

Few perennial forages, with the exception of M. sativa L., are suitable for low rainfall

environments in the agricultural regions of southern Australia. Dorycnium hirsutum (L.)

Ser. and D. rectum (L.) Ser. are potential alternative perennial forage legumes under

evaluation to complement M. sativa. Strategies for surviving periods of water deficit are

vital for perennial plants in these water-limited environments. This experiment

compared physiological responses to increasing water deficit among D. hirsutum, D.

rectum and M. sativa. Plants were grown in the glasshouse in large pots (1 m deep, 10

cm diameter) containing a sandy clay loam (14% available water content). Watering

was withheld for 21 days and predawn and midday leaf water potential, leaf osmotic

potential and relative leaf water content were determined, and mid morning rates of gas

exchange rates were measured at 5 times as soil water was depleted. After an additional

2 weeks of severe water deficit plant recovery was measured. Pressure-volume

relationships for each species were also investigated.

D. hirsutum and M. sativa displayed similar physiological responses to increasing water

deficit. Both species reduced stomatal conductance at leaf water potentials below -1.8

MPa and had osmotically adjusted by approximately 0.5 MPa by the end of the period

of drought. D. rectum differed from the other species; leaf water potential was

maintained until soil water content was very low when leaf water potential dropped

rapidly. D. rectum did not accumulate osmotica or show leaf morphological adaptations

to water deficit. Only 20% of D. rectum plants survived the period of severe water

deficit compared with 100% for D. hirsutum and 80% for M. sativa. D. hirsutum and M.

sativa appear to possess physiological and morphological adaptations that enable them

to overcome periods of water deficit. The physiology of D. rectum is distinct from D.

hirsutum and M. sativa and does not seem to be suitable for overcoming extended

periods of water deficit.

Chapter 7: Adaptations to water deficit in Dorycnium

144

Introduction

Periods of water deficit are common across the agricultural regions of Australia. In the

past, pasture production in these regions has mainly relied upon annual plants that can

quickly grow and reproduce during the wet season and survive the dry season as seed,

thus avoiding severe drought (Turner 2004). However, systems that rely entirely on

annual plants are unsustainable and the integration of perennial pastures is needed to

reduce problems such as dryland salinity (Cocks 2001). Perennials need to be able to

resist or tolerate periods of water deficit to survive. Of the current array of herbaceous

perennial legumes, Medicago sativa L. (lucerne, alfalfa) is the most tolerant of low

rainfall environments (< 450 mm mean annual rainfall), where growing seasons are

short, and long and intense periods of water deficit are experienced. The tolerance of M.

sativa to these conditions is related to its ability to access water from the subsoil and its

ability to remain dormant when water supply is limited (Sheaffer et al. 1988).

Two potential alternative perennial forages for southern Australia are Dorycnium

hirsutum (L.) Ser. and D. rectum (L.) Ser. (Bennett 2002; Dear et al. 2003). Both

species originate from Mediterranean regions of Europe, Africa and West Asia with

similar climates to southern Australia (Chapter 3). D. hirsutum has been found to be

drought tolerant in experiments in Australia (Chapter 5)(Lane et al. 2004) and New

Zealand (Wills 1983; Sheppard and Douglas 1986; Douglas et al. 1996). The deep root

systems of D. hirsutum and M. sativa allow extraction of water from deep soil layers

during periods of low rainfall (Chapter 4), but a range of other physiological and

morphological adaptations to drought are likely to play a role in their tolerance to water

deficit. D. rectum is reported to occur mostly on moist sites or where water is readily

available (Demiriz 1970) and appears to be less successful in drought-prone

environments. Field experiments in Western Australia show that D. rectum survival was

inferior to D. hirsutum under water-limited conditions during its year of establishment

(Bell et al. 2005) (Chapter 5). This lesser drought tolerance of D. rectum seedlings

could be due to differences in root morphology, with D. hirsutum more quickly

developing a deep root system (Bell 2005) (Chapter 6). Beside root morphology, other

strategies that D. hirsutum and D. rectum use to tolerate water deficit have not been

investigated.

145

More generally, in addition to deep root systems, a range of morphological and

physiological adaptations to avoid or tolerate water deficit are found in plants. These

include (adapted from Begg and Turner (1976)):

• Regulation of water use by stomatal closure in response to declining leaf turgor.

This enables plants to photosynthesise when evaporative demand is low in the

morning and evening, and conserve water when evaporative demand is high

during the middle of the day.

• Osmotic adjustment via the net accumulation of solutes in the leaf under water

deficit. This lowers leaf osmotic potential and contributes to the maintenance of

leaf turgor.

• Minimisation of leaf area to reduce the rate of water loss from the soil. This slows

the development of water deficit and can involve leaf shedding or accelerated

senescence of older leaves, leaf movement to reduce incident radiation, and leaf

flagging or rolling reduce effective leaf area.

• Formation of trichomes or leaf hairs and cuticular waxes. These can increase

reflection of radiation and reduce water conductance through the leaf boundary

layer, thus reducing water loss and moderating leaf temperature.

This experiment compared a selection of these responses to increasing water deficit

among D. rectum, D. hirsutum and M. sativa. It was hypothesised that the three species

would differ in their physiological and morphological adaptations to water deficit,

which would reflect differences in tolerance to drought in the field. To reduce the

effects of different root morphologies plants were grown in pots with in a set soil

volume, but large enough to closely represent the development of water deficit in the

field. Observations of plant survival following rewatering after a period of severe water

deficit were also made.

Materials and Method

Experimental design

The experiment was carried out in the glasshouses at the University of Western

Australia, Perth, Australia (31º59´S, 115º53É). Plants were grown in 7.9 L freely

drained pots (1 m deep, 10 cm diameter) to ensure slow soil drying. In each pot 400 g of

coarse gravel was placed in the bottom and 11 kg of air dried sandy clay loam soil,


146

collected from CSIRO Yallanbee Research Station, Bakers Hill, Western Australia

(31º45´S, 116º29É), added above the gravel. Soil was allowed to settle to a bulk

density of 1.48 g cm-3. The moisture retention characteristics of the soil were

determined using the pressure plate technique (Moore et al. 2004). The soil was packed

into rings at the same bulk density to that in the pots and the gravimetric water content

corresponding to 0 kPa (saturated), 10 kPa (field capacity), 100 kPa and 1500 kPa

(permanent leaf wilting point) (PWP) determined (Table 1). Total available water

content (i.e. field capacity – leaf wilting point) was 13.8% w/w.

Table 1. Soil water characteristics of sandy clay loam soil used in the glasshouse experiment, as

determined by the pressure plate method.

Soil water potential (kPa)

Soil water content (w/w % ± se)

0 32.2 ± 0.4

10 18.1 ± 0.2

100 8.4 ± 0.1

1500 4.3 ± 0.1

Five replicate pots of M. sativa (cv. Sceptre), D. hirsutum (accession TAS 1002) and D.

rectum (accession TAS 1274) were allocated to the glasshouse bench in a split-plot

design. Sowing of seeds was staggered, based on data from Bell (2005)(Chapter 6), in

an attempt to achieve similar plant size at the initiation of the drought treatments; 12

July for D. hirsutum, 19 July for D. rectum and 9 August for M. sativa. Ten seeds were

sown per pot and seedlings were thinned to 1 plant per pot approximately 4 weeks after

sowing. Basal nutrients were applied per kg of oven dreid soil as follows: 14 mg kg-1

MgCl2; 133 mg kg-1 Ca(H2PO4); 200 mg kg-1 K2SO4; 10 mg kg-1 MnSO4; 10 mg kg-1

ZnSO4; 2 mg kg-1 CuSO4; 67 µg kg-1 H3BO3; 33 µg kg-1 CoSO4 and 17 µg kg-1

Na2MoO4. The nutrients were added in a solution to soil surface before sowing.

Appropriate Rhizobium, group AL for M. sativa and WSM 1293 for Dorycnium (same

as Lotus corniculatus L.) (Wills et al. 1989), were irrigated onto the soil surface three

days after sowing (DAS). A small amount of nitrogen (100 mg kg-1 NH4NO3) was also

added to aid early growth of seedlings before effective nodules had been formed.

Glasshouse temperatures throughout the experiment are provided in Fig. 1.

147

0

5

10

15

20

25

30

35

40

45

12 J

ul.

29 J

ul.

15 A

ug.

1 S

ep.

18 S

ep.

5 O

ct.

22 O

ct.

8 N

ov.

25 N

ov.

12 D

ec.

29 D

ec.

Air

tem

pera

ture

(oC

)

BA C

0

5

10

15

20

25

30

35

40

45

12 J

ul.

29 J

ul.

15 A

ug.

1 S

ep.

18 S

ep.

5 O

ct.

22 O

ct.

8 N

ov.

25 N

ov.

12 D

ec.

29 D

ec.

Air

tem

pera

ture

(oC

)

BA C

Figure 1. Maximum (●) and minimum (○) air temperature in the glasshouse during the

experiment. Vertical lines indicate the dates of initiation of drought treatment (A), completion

of physiological measurements (B) and rewatering of plants (C).

Plate 1. D. hirsutum plants at the initiation of drought treatments.

Plants were watered ad libitum until the root system of all plants had fully explored the

soil in the pot; spare pots of each species were examined to ensure this was the case. All

pots were watered to field capacity on the afternoon of 25 November 2004 and


148

physiological measurements were initiated out on 26 November 2004. Watering then

ceased for the drought treatment, and well-watered control pots were watered to weight

(field capacity) twice a week and in the afternoon before measuring physiological

parameters. Plants size at this time was sufficient that repeated sampling of leaves

represented a small percentage of plant biomass (Plate 1).

Physiological measurements

Physiological measurements were carried out on droughted and well-watered plants 6,

10, 13, 17 and 21 days after water was withheld. Pots were weighed and the

corresponding soil water content (SWC) determined. Leaf water potential was measured

predawn (0300–0500 hrs) and at midday (1200–1400 hrs) in a pressure chamber on

petioles for lucerne and stems of Dorycnium species (petioles were too short). Samples

were immediately placed in a water tight vial, snap frozen on dry ice and stored in a

freezer at -20ºC. Samples were later thawed, sap expressed using a leaf press and sap

osmolarity measured using a freezing point osmometer (Fiske Associates,

Massachusetts). Osmotic potential (π) of samples was determined using equation 1.

Osmotic potential at full turgor (πsat) (100% relative leaf water content) was calculated

(Equation 2) to allow comparisons between leaves at the same water content. Relative

leaf water content (RLWC) was measured predawn and at midday (Equation 3). Leaves

were removed adjacent to those used for water potential measurements and their fresh

mass measured immediately. Turgid mass was measured after they had been floated on

deionised water overnight. Dry mass was measured after samples were dried in a 70ºC

oven for 2 days.

(1) 1000

447.2 osmolarity× = π

(2) 100

RLWCsat

× = ππ

(3) 100×−−

= dryturgid

dryfresh

MassMass

MassMassRLWC

CO2 and H2O exchange were measured between 0900 hrs and 1100 hrs using a LI-6400

with LED light source (LI-COR, Nebraska). Newly expanded leaves were enclosed in

the chamber for approximately 2 minutes and allowed to equilibrate. The light level was

set at 1500 µmol m-2 s-1, flow rate at 500 µmol s-1, [CO2] to 400 µmol mol-1, leaf

149

temperature to 25ºC and relative humidity was maintained between 33 and 42%. After

measurements were logged, leaves were marked and later used for midday RLWC. Leaf

area within the cuvette was determined using a WinRHIZO scanner and software

(Régent Instruments Inc., Quebec) after turgid leaf weights were obtained.

Photosynthetic parameters were calculated on a leaf area and dry mass basis.

Pressure-volume relationship

Samples were removed from the terminal stems of well-watered plants of D. hirsutum,

D. rectum and M. sativa at 0800 hrs on 2 December 2004 (7 days after commencing

drought treatments) and submerged in deionised water for 2 hours in a test tube until

fully hydrated. Surface water was removed from the sample and the mass measured.

The pressure volume relationships were then determined from alternate measurements

of sample mass and stem water potential, using a pressure chamber. After completion,

samples were dried in an oven at 70ºC for 2 days, dry mass measured and RLWC of

samples at each measurement calculated (Equation 3). Pressure volume curves were

fitted as for Turner (1981) and osmotic potential at full turgor and the turgor loss point

were extrapolated. Volumetric modulus of elasticity (ε) was calculated and used to

estimate maximum bulk elastic modulus (εmax) (Turner 1981).

Recovery after drought

Once pot weight had declined below a soil water content of 4% w/w (corresponding to

soil water potential of -1.5 MPa or permanent wilting point), watering was withheld for

a further 2 weeks, with pot weight measured weekly. After 2 weeks pots were rewatered

to field capacity and plant survival recorded after 10 days.


All data were subjected to an analysis of variance using Genstat version 6 (Genstat 6

Committee 2002) and regression analysis was used to determine relationships between

parameters.

Results

Plant water status

Leaf water potentials were similar for M. sativa and D. hirsutum as soil water content

declined (Fig. 2a and 2b). Predawn leaf water potentials remained constant (> –0.7


150

MPa) until soil water content declined below 8% w/w, when 73% of available water had

been used. On average, midday leaf water potential was 1.0 MPa lower than predawn

measurements and began to decline at higher soil water contents (SWC of 10% w/w).

When soil water content was at 4% w/w (PWP), leaf water potentials of M. sativa and

D. hirsutum reached less than –3.0 MPa.

D. rectum showed similar leaf water potentials at predawn and midday and plants did

not display the same pattern of decline in plant water status as observed for D. hirsutum

and M. sativa (Fig. 2c). It appeared that D. rectum maintained leaf water potentials until

a threshold water deficit was reached, resulting in an abrupt decline in leaf water

potential at soil water contents < 8% w/w at midday and < 6% w/w predawn. However,

this threshold was not consistent among individual plants.

In D. hirsutum and M. sativa, the decline in RLWC was similar to that for leaf water

potential. However, differences between midday and predawn for relative leaf water

content were not as evident as those for leaf water potential. Nonetheless, a clear linear

relationship was observed between RLWC and leaf water potential. This correlation was

not as strong for D. rectum and leaf water potential and RLWC were not as closely

related in this species.

Figure 2. Predawn (open) and midday (solid) leaf water potential and relative leaf water content (RLWC) at declining soil water content and the relationship between RLWC and leaf water potential for (a) M. sativa, (b) D. hirsutum and (c) D. rectum (dashed line represents soil water potential of -1.5 MPa or permanent leaf wilting point (PWP)). All regressions have a P<0.001.

PWP

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

00.050.10.150.20.25Soil water content (w/w)

RLW

C

PWP

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0


RLW

C

PWP

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0


RLW

C

(a) M. sativa

PWP

-4.5

-4.0

-3.5

-3.0

-2.5

-2.0

-1.5

-1.0

-0.5

0.0


Leaf

wat

er p

oten

tial (

MP

a)

(b) D. hirsutum

PWP

-4.5

-4.0

-3.5

-3.0

-2.5

-2.0

-1.5

-1.0

-0.5

0.0


Leaf

wat

er p

oten

tial (

MP

a)

(c) D. rectum

PWP

-4.5

-4.0

-3.5

-3.0

-2.5

-2.0

-1.5

-1.0

-0.5

0.0


Leaf

wat

er p

oten

tial (

MP

a)

y = -4.53x

r2 = 0.52

-4.5

-4.0

-3.5

-3.0

-2.5

-2.0

-1.5

-1.0

-0.5

0.0

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.01 - RLWC

Leaf

wat

er p

oten

tial (

MP

a)

y = -5.34x

r2 = 0.78

-4.5

-4.0

-3.5

-3.0

-2.5

-2.0

-1.5

-1.0

-0.5

0.0

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.01 - RLWC

Leaf

wat

er p

oten

tial (

MP

a)

y = -6.8x

r2 = 0.70

-4.5

-4.0

-3.5

-3.0

-2.5

-2.0

-1.5

-1.0

-0.5

0.0

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.01 - RLWC

Leaf

wat

er p

oten

tial (

MP

a)


152

Figure 3. Changes in calculated osmotic potential at full turgor (π sat) in leaves of (a) M. sativa,

(b) D. hirsutum and (c) D. rectum sampled at midday from well-watered (solid) and droughted

plants (open) (l.s.d. at P<0.05).

Osmotic adjustment

Changes in osmotic potential at full turgor, which is indicative of osmotic adjustment,

contributed to reductions in the leaf osmotic potential of 0.46 and 0.53 MPa in M. sativa

and D. hirsutum, respectively (Fig 3a and 3b). Average midday relative leaf water

content at this time was 28 ± 2 % for M. sativa and 53 ± 2% for D. hirsutum. The

osmotic potential at full turgor of droughted D. rectum leaves was always lower than for

well-watered plants, but no consistent change in osmotic potential at full turgor in

(c) D. rectum

l.s.d.

-1.8

-1.6

-1.4

-1.2

-1.0

-0.8

-0.6

0 3 6 9 12 15 18 21

Days after initiation of water stress

π s

at

(b) D. hirsutum

l.s.d.

-1.8

-1.6

-1.4

-1.2

-1.0

-0.8

-0.6

π s

at(a) M. sativa

l.s.d.

-1.8

-1.6

-1.4

-1.2

-1.0

-0.8

-0.6π

sat

153

response to increased water stress (Fig. 3c). In all species, saturated osmotic potential of

leaves sampled at midday was 0.15–0.19 MPa lower than those at predawn.

Photosynthetic responses

All species showed reduced photosynthesis and stomatal conductance in response to

declining water status (Fig. 4). Stomatal conductance in M. sativa and D. hirsutum was

substantially reduced once leaf water potential declined below -1.8 MPa. Photosynthesis

in M. sativa and D. hirsutum declined in response to similar reductions in leaf water

potential (Fig. 4a and 4b). However, in droughted D. rectum plants, stomatal

conductance and photosynthesis were reduced even though no reduction in leaf water

potential was observed.

Stomatal conductance and photosynthetic rate of unstressed D. rectum plants were

lower than for D. hirsutum and M. sativa (Fig. 4). For example, mean stomatal

conductance on a leaf area basis was 2.23 ± 0.27 mol m-2 s-1 for M. sativa and 1.99 ±

0.42 mol m-2 s-1 for D. hirsutum compared to 1.23 ± 0.18 mol m-2 s-1 for D. rectum.

However, due to the lower specific leaf area of D. hirsutum (Table 2) its photosynthetic

rate on a leaf dry mass basis was lower than for M. sativa, being more similar to D.

rectum (M. sativa, 523 ± 38 µmol g-1 s-1; D. hirsutum, 346 ± 68 µmol g-1 s-1; and D.

rectum, 371 ± 20 µmol g-1 s-1).

Table 2. Specific leaf area of droughted and well-watered M. sativa, D. hirsutum and D. rectum,

measured after the initiation of drought treatments.

Specific leaf area (m2/kg) Species

Water stressed Well-watered mean

M. sativa 20.0 20.3 20.1

D. hirsutum 11.6 15.0 13.3

D. rectum 17.8 18.2 18.0

l.s.d. (P=0.05) 1.7 1.2

Figure 4. Relationship between midday leaf water potential and photosynthetic rate and stomatal conductance (gS,w) for well-watered (solid) and water-stressed

plants (open) of (a) M. sativa, (b) D. hirsutum and (c) D. rectum. The exponential relationships displayed for: stomatal conductance were, y = 7806e1.413x (r2 = 0.76)

for M. sativa and y = 2798e1.074x (r2 = 0.73) for D. hirsutum; and for photosynthesis, y = 63.3e0.798x (r2 = 0.81) for M. sativa and y = 45.5e0.630x (r2 = 0.59) for D.

hirsutum.

(a) M. sativa

0

5

10

15

20

25

30

35

40

45

50P

hoto

synt

hesi

s (u

mol

m-2

s-1)

0

500

1000

1500

2000

2500

3000

-4.5-4-3.5-3-2.5-2-1.5-1-0.50

Leaf water potential (MPa)

gS,w

(m

mol

m-2

s-1

)

0

500

1000

1500

2000

2500

3000

-4.5-4-3.5-3-2.5-2-1.5-1-0.50


gS,w

(m

mol

m-2

s-1

)

(b) D. hirsutum

0

5

10

15

20

25

30

35

40

45

50

Pho

tosy

nthe

sis

(um

ol m

-2 s-1

)

(c) D. rectum

0

5

10

15

20

25

30

35

40

45

50

Pho

tosy

nthe

sis

(um

ol m

-2 s

-1)

0

500

1000

1500

2000

2500

3000

-4.5-4-3.5-3-2.5-2-1.5-1-0.50


gS,w

(m

mol

m-2

s-1

)


155

Despite differences in maximum rate of photosynthesis of unstressed plants,

photosynthetic water use efficiency (WUE) (A/gSw) was similar in all species;

averaging 44 ± 5 nmol/mmol for D. rectum, 34 ± 8 nmol/mmol for M. sativa and 36 ± 6

nmol/mmol for D. hirsutum (Fig. 5). A similar ratio of internal to external CO2

concentrations was also calculated in the three species at these times (Fig. 5). WUE

increased at the last measurement in all species when internal CO2 concentration

declined (Fig. 5). This coincided with higher midday leaf water potentials in D. rectum

(-2.6 MPa) than in M. sativa or D. hirsutum (< -4.0 MPa).

Pressure-volume curves

Pressure-volume analysis of undroughted plants revealed similar findings for both D.

hirsutum and M. sativa (Table 3). However, D. rectum exhibited a lower water potential

at turgor loss point (TLP) than D. hirsutum or M. sativa. This difference was largely

explained by a higher osmotic potential, and thus RLWC at turgor loss point was similar

in all species. Despite the higher osmotic potential calculated in D. rectum in the

pressure-volume analysis, osmotic potential measured using an osmometer was the

same in all species. The data suggest that the cells in D. rectum leaves had a higher bulk

elastic modulus, and thus were less elastic than the cells of D. hirsutum or M. sativa, but

this appeared to have minor impact on the turgor loss point.

Table 3. Water potential (-Ψ TLP) and relative water content (RWCTLP) at turgor loss point,

saturated osmotic potential (-Ψπ,sat) and bulk elastic modulus (εmax) of M. sativa, D. hirsutum

and D. rectum determined using pressure-volume analysis. Saturated osmotic potential

measured using an osmometer is also presented. (mean ± sem)

Species -Ψ Ψ Ψ Ψ TLP (MPa)

RWCTLP -ππππ sat (MPa)

Osmometer

-ππππ sat (MPa) εmax

M. sativa 1.13 ± 0.13 0.82 ± 0.03 0.92 ± 0.08 1.02 ± 0.05 4.8 ± 0.7

D. hirsutum 1.38 ± 0.07 0.87 ± 0.02 1.04 ± 0.04 1.05 ± 0.03 4.3 ± 0.3

D. rectum 1.59 ± 0.11 0.86 ± 0.01 1.29 ± 0.06 1.03 ± 0.05 8.6 ± 1.7

Figure 5. Changes in photosynthetic water use efficiency (A/gSw) and the ratio of internal and external CO2 concentration (Ci/Ca) with declining soil water content

in (a) M. sativa, (b) D. hirsutum and (c) D. rectum (mean ± sem) (dashed line represents soil water potential of -1.5 MPa or permanent leaf wilting point (PWP)).

PWP

0.00.1

0.20.3

0.40.5

0.60.7

0.80.9

1.0

00.050.10.150.2

Soil water content (w/w)

Ci /C

a

PWP

0.0

0.10.2

0.3

0.40.5

0.6

0.7

0.80.9

1.0

00.050.10.150.2


PWP

0.0

0.10.2

0.3

0.40.5

0.6

0.7

0.80.9

1.0

00.050.10.150.2


(c) D. rectum

PWP0.00

0.05

0.10

0.15

0.20

0.25

0.30

A/E

(um

ol m

mol

-1)

(b) D. hirsutum

PWP0.00

0.05

0.10

0.15

0.20

0.25

0.30

A/E

(um

ol m

mol

-1)

(a) M. sativa

PWP0.00

0.05

0.10

0.15

0.20

0.25

0.30

A/g

S w

(um

ol m

mol

-1)

157

Leaf morphological adaptations

A number of leaf morphological adaptations to water deficit were observed among the

three species. Trichomes (leaf hairs) were very evident on the leaves of D. hirsutum,

and to a lesser extent in D. rectum, but were not observed on M. sativa (Plate 2). Both

D. hirsutum and M. sativa leaves reacted to reduce radiation interception as water

deficit developed (Plate 3). Specific leaf area of droughted D. hirsutum plants was also

lower than in well-watered plants, while no difference was observed for M. sativa or D.

rectum (Table 2).

Plate 2. Comparison of leaf pubescence in (a) M. sativa, (b) D. hirsutum and (c) D. rectum

Plate 3: Leaf movements to reduce effective leaf area in (a) M. sativa and (b) D. hirsutum.

(a) M. sativa (b) D. hirsutum

(b) D. hirsutum (a) M. sativa (c) D. rectum


158

Recovery after drought

After 2 weeks of soil water content being below 4% w/w (i.e. -1.5 MPa or permanent

leaf wilting point) followed by 10 days of watering to field capacity all D. hirsutum

plants survived, while 80% of M. sativa and 20% of D. rectum plants survived.

Extraction of water from the soil was negligible during this period and plants of all

species proceeded to senesce leaves. Stems of lucerne and D. hirsutum appeared to be

dead but upon rewatering plants were able to reshoot from the base. However, once all

green leaves on D. rectum plants had died, plants failed to respond when water status

was restored.

Discussion

This study has identified some distinct physiological and morphological adaptations to

water deficit among D. rectum, D. hirsutum and M. sativa. The implications of these for

the ability of these species to tolerate periods of water deficit will now be discussed.

Physiological adaptations

D. hirsutum and M. sativa displayed similar physiological responses to increasing water

deficit. First, both species exhibited the capacity to reduce stomatal conductance as

water deficit increased, but this did not completely prevent the development of further

water deficit. In field-based studies, M. sativa stomatal conductance decreased at leaf

water potentials of -1.2 to -1.5 MPa with minimums typically reached at -2.5 MPa

(Sheaffer et al. 1988). In the present study a large decline in stomatal conductance in M.

sativa was associated with midday leaf water potentials of less than -1.8 MPa. Secondly,

both D. hirsutum and M. sativa displayed some degree of osmotic adjustment as water

deficit developed. Osmotic adjustment is known to occur in M. sativa, with proline

concentration increasing in the phloem and in droughted leaves, which is presumably a

mechanism for maintenance of leaf turgor (Irigoyen et al. 1992b; Girousse et al. 1996).

These two mechanisms may play a significant role in the tolerance of these two species

to water deficits.

In contrast to the similar responses of D. hirsutum and M. sativa, D. rectum displayed

somewhat puzzling physiological responses to increasing water deficit. It appears that

D. rectum attempts to maintain high plant water status irrespective of the level of water

supply. This might be achieved if plants could translocate water quickly and/or store in

159

plant tissues a large amount of water. The thick fleshy stems of D. rectum are consistent

with the latter scenario, but the process by which leaf water potential is maintained is

unknown. Once water supply is insufficient to maintain high plant water status the rapid

decline in leaf water potential suggests that D. rectum does not have appropriate

strategies to control reductions in leaf water potential. Indeed, adaptations to maintain

leaf turgor, such as cell elasticity and osmotic adjustment, were lower in D. rectum than

in D. hirsutum and M. sativa. Despite the apparent maintenance of leaf water potential,

D. rectum exhibited a reduction in stomatal conductance in water-stressed plants. Begg

and Turner (1976) assert that stomata close when leaf turgor declines below a critical

value, but in D. rectum stomatal closure was more closely related to RLWC. Leaf water

potential is not closely related to turgor, and osmotic and matric effects may play a role.

Even though all care was taken, the unusual response observed in D. rectum may have

resulted from a false determination of the end point at balancing pressure in the chamber

when measuring leaf water potential, and these results may be an artifact of this

difficulty.

In addition to differences in plant physiological responses as water stress developed,

differences in stomatal conductance and photosynthetic rate among well-watered plants

of each species were evident. M. sativa and D. hirsutum displayed higher stomatal

conductance than D. rectum when leaf water status was high. High stomatal

conductances (625 – 1250 mmol m-2 s-1) are common in M. sativa (Sheaffer et al. 1988)

and might be indicative of higher stomata density and/or larger stomata apertures than

D. rectum. However, high stomatal conductance (>1000 mmol m-2 s-1) were measured

in all species in this study.

The differences in the photosynthesis rate of well-watered plants among the species are

consistent with their plant growth rate characteristics. M. sativa had a higher relative

growth rate (i.e. growth increment per unit of plant mass) than D. hirsutum and D.

rectum (Bell 2005) (Chapter 6), and, as anticipated, displayed a higher rate of

photosynthesis per gram of leaf. The lower photosynthesis rate per unit leaf area

observed for D. rectum in the present study is analogous with the lower net assimilation

rate previously recorded (i.e. growth increment per unit leaf area) (Bell 2005) (Chapter

6). In the present experiment and Bell (2005) (Chapter 6) assimilation per unit leaf area

was similar for D. hirsutum and M. sativa, but the lower specific leaf area of D.


160

hirsutum explains the lower assimilation per unit mass. Despite the differences in

photosynthesis rate, it is surprising that no difference in photosynthetic water use

efficiency was observed among M. sativa, D. hirsutum and D. rectum. All species use

the C3 photosynthetic pathway, but it might be expected that M. sativa might be higher,

having received the greatest selection for biomass production.

A result of interest in the current experiment was that in all species reductions in

stomatal conductance were not associated with a decline in the ratio of internal to

external CO2 concentration. Internal CO2 concentration was unaffected until the final

measurement (Fig. 5), when water deficits were far greater than those required to close

stomata (< -3.0 MPa midday ψleaf) and photosynthetic rate was already reduced (Fig. 4).

Similar observations have previously been made in M. sativa (Irigoyen et al. 1992a) and

a range of other species (Begg and Turner 1976). CO2 exchange may be still occurring

due to cuticular conductance or incomplete stomatal closure. Carter and Sheaffer

(1983b) recorded stomatal conductance of 45–125 mmol m-2 s-1 when leaf water

potential had fallen below -2.5 MPa in M. sativa. In the present study, internal CO2

concentration was maintained until stomatal conductance declined below about 50

mmol m-2 s-1. The results suggest that CO2 concentration was not responsible for the

decline in rate of photosynthesis. Non-stomatal reductions in photosynthesis have been

attributed to water stress impacts on the photosynthetic pathway through the inhibition

of chloroplast activity (Boyer and Bowen 1970; Boyer and Potter 1973). This is

consistent with the results of the present experiment where the proportional decline in

photosynthesis and transpiration as water stress developed meant that photosynthetic or

water use efficiency did not improve.

Morphological adaptations

Leaf morphological adaptations to water-limiting conditions were observed in D.

hirsutum and M. sativa and may also contribute to their greater tolerance of water

deficits compared with D. rectum. The leaves and stems of D. hirsutum are particularly

pubescent. Leaf pubescence increases the boundary layer and thus decreases the

transpiration water loss (Grammatikopoulous and Manetas 1994). Leaf trichomes can

also reduce heat load by reflecting radiation and reducing the absorption of

photosynthetically active radiation (Begg and Turner 1976). Radiation interception was

also reduced by heliotropic leaf movements in both D. hirsutum and M. sativa. The

phenomenon of leaf cupping has been previously documented in M. sativa and occurs in

161

conjunction with midday decline in leaf water potential (Travis and Reed 1983). In this

study, it was also observed that specific leaf area of water-stressed D. hirsutum plants

was significantly lower than in well-watered plants. This apparent plasticity in D.

hirsutum may be associated with adjustments in leaf morphology as stress increases.

It was also observed that whole stems of D. hirsutum and M. sativa died after a short

period of severe water deficit, but plants responded upon rewatering, while in D. rectum

once all green leaves had been lost plants failed to respond to rewatering. It is widely

recognized that M. sativa plants will shed leaves during severe water stress and assume

a semi-dormant state until water supply is improved (Carter and Sheaffer 1983a;

Irigoyen et al. 1992a). D. hirsutum also appears to sacrifice stems and leaves in order to

maintain water status in buds and meristems near the base of the plant during severe

water stress. It is possible that xylem vessels of M. sativa and D. hirsutum cavitate more

readily than D. rectum and reduce water loss by shutting down older stems (Tyree and

Ewers 1991), but this has not been documented elsewhere in these species and was not

investigated in this study.

Conclusions

The experiment demonstrated that D. hirsutum and M. sativa have similar physiological

responses when subjected to water deficit. Leaf morphological adaptations in D.

hirsutum and M. sativa may contribute to their ability to handle water deficit. However,

adaptations, such as osmotic adjustment, and an ability to survive severe water deficit,

observed in D. hirsutum and M. sativa were absent in D. rectum. Thus, there appears to

be some physiological basis for the poorer survival of D. rectum than D. hirsutum in the

field (Chapter 5 or Bell et al. 2005). Based on the physiological parameters measured in

this chapter, D. rectum does not appear to be adapted to dry environments unlike D.

hirsutum.

References

Begg JE, Turner NC (1976) Crop water deficits. Advances in Agronomy 28, 161-217. Bell LW (2005) Relative growth rate, resource allocation and root morphology in the perennial legumes, Medicago sativa, Dorycnium rectum and D. hirsutum grown under controlled conditions. Plant and Soil 270, 199-211.


162

Bell LW, Moore GA, Ewing MA, Bennett SJ (2005) Establishment and summer survival of the perennial legumes, Dorycnium hirsutum and D. rectum in mediterranean environments. Australian Journal of Experimental Agriculture 45, 1245-1254. Bennett SJ (2002) Distribution and economic importance of perennial Astragalus, Lotus and Dorycnium. In 'New Perennial Legumes for Sustainable Agriculture'. (Ed. SJ Bennett) pp. 90-115. (University of Western Australia Press: Crawley, Western Australia) Boyer JS, Bowen BL (1970) Inhibition of oxygen evolution in chloroplasts isolated from leaves with low water potentials. Plant Physiology 45, 612-615. Boyer JS, Potter JR (1973) Chloroplast response to low leaf water potentials. Part 1, Role of turgor. Plant Physiology 51, 989-992. Carter PR, Sheaffer CC (1983a) Alfalfa response to soil water deficits. I. Growth, forage quality, yield, water use and water-use efficiency. Crop Science 23, 669-675. Carter PR, Sheaffer CC (1983b) Alfalfa response to soil water deficits. II. Plant water potential, leaf conductance and canopy temperature relationships. Crop Science 23, 676-680. Cocks PS (2001) Ecology of herbaceous perennial legumes: a review of characteristics that may provide management options for the control of salinity and waterlogging in dryland cropping systems. Australian Journal of Agricultural Research 52, 137-151. Dear BS, Moore GA, Hughes SJ (2003) Adaptation and potential contribution of temperate perennial legumes to the southern Australian wheatbelt: a review. Australian Journal of Experimental Agriculture 43, 1-18. Demiriz H (1970) Dorycnium Miller. In 'Flora of Turkey and East Aegean Islands'. (Ed. PH Davis) pp. 512-518. (Edinburgh University Press: Edinburgh) Douglas GB, Wills BJ, Pryor HN, Foote AG, Trainor KD (1996) Establishment of perennial legume species in drought-prone, North and South Island sites. Proceedings of the New Zealand Grassland Association 58, 253-257. GenStat 6 Committee (2002) GenStat 6th Edition 6.1.0.200. Lawes Agricultural Trust, Rothamsted UK. Girousse C, Bournoville R, Bonnemain J-L (1996) Water deficit-induced changes in concentrations in proline and some other amino acids in the phloem sap of alfalfa. Plant Physiology 111, 109-113. Grammatikopoulous G, Manetas Y (1994) Direct absorption of water by hairy leaves of Pholomis fruticosa and its contribution to drought avoidance. Canadian Journal of Botany 72, 1805-1811. Irigoyen JJ, Emerich DW, Sanchez-Diaz M (1992a) Alfalfa leaf senescence induced by drought stress: photosynthesis, hydrogen peroxide metabolism, lipid peroxidation and ethylene evolution. Physiologia Plantarum 84, 67-72.

163

Irigoyen JJ, Emerich DW, Sanchez-Diaz M (1992b) Water stress induced changes in concentrations of proline and total soluble sugars in nodulated alfalfa (Medicago sativa) plants. Physiologia Plantarum 84, 55-60. Lane PA, Davies SR, Hall EJ, Moore GA (2004) 'Dorycnium species as alternative forage plants.' Rural Industries Research and Development Corporation, Report No. 04/159. Moore GA, Hall D, Russell JS (2004) Physical factors affecting water infiltration and redistribution - Soil water. In 'Soilguide. A handbook for understanding and managing agricultural soils'. (Ed. GA Moore). (Department of Agriculture, Western Australia: Perth, Western Australia) Sheaffer CC, Tanner CB, Kirkham MB (1988) Alfalfa Water Relations and Irrigation. In 'Alfalfa and Alfalfa Improvement'. (Eds AA Hanson, DK Barnes, RR Hill Jr) pp. 373-409. (American Society of Agronomy, Crop Science Society of America and Soil Science Society of America: Madison, Wisconsin, USA) Sheppard JS, Douglas GB (1986) Management and uses of Dorycnium spp. Water and Soil Miscellaneous Publication 94, 260-262. Travis RL, Reed R (1983) The solar tracking pattern in a closed alfalfa canopy. Crop Science 23, 664-668. Turner NC (1981) Techniques and experimental approaches for the measurement of plant water status. Plant and Soil 58, 339-366. Turner NC (2004) Sustainable production of crops and pastures under drought in a Mediterranean environment. Annals of Applied Biology 144, 139-147. Tyree MT, Ewers FW (1991) Tansley review No. 34. The hydraulic architecture of trees and other woody plants. New Phytologist 119, 345-360. Wills BJ (1983) 'Forage plants for the semi-arid high country and rangelands of New Zealand.' Centre of Resource Management, Lincoln College, Special Publication 26, Canterbury, New Zealand. Wills BJ, Begg JSC, Foote AG (1989) Dorycnium species - Two new legumes with potential for dryland pasture rejuvenation and resource conservation in New Zealand. Proceedings of the New Zealand Grassland Association 50, 169-174.

Chapter 8: Production, survival and nutritive value of the

perennial legumes Dorycnium hirsutum and D. rectum

subjected to different cutting heights

Abstract

Dorycnium hirsutum and D. rectum are perennial legumes which may have potential for

use as pastures for the control of groundwater recharge in southern Australia. Little is

known about the quality of the forage of Dorycnium species for grazing livestock or

how these species respond to cutting. The effect of cutting height on plant survival,

production of dry matter (DM), the proportion of leaf, edible stem (approximately < 5

mm diameter) and woody stem in the DM and the nutritive value of the edible

components was investigated. Biomass from five cutting-height treatments (uncut,

ground level, 5 or 8 cm, 10 or 15 cm and 15 or 30 cm above ground level) was removed

at 8-weekly intervals from plots of D. hirsutum and D. rectum from September 2002 to

July 2003.

In both species, plants subjected to lower cutting height treatments produced less DM

above the height of the cut than those cut at higher heights. Dry matter production

declined over time in all treatments. Plants cut to ground level failed to regrow after the

second harvest for D. hirsutum and the fourth harvest for D. rectum. Thus, these

Dorycnium species were intolerant of high severity defoliations at 8-week intervals.

Negligible inedible woody stem was present in regrowth of both species after 8 weeks

but D. hirsutum regrowth had a higher proportion of leaf (0.72) than D. rectum (0.56).

Plants left uncut accumulated a large amount of inedible woody stem (0.69 in both

species by July 2003), particularly at the base of the plant.

Edible DM from regrowth of D. hirsutum and D. rectum had crude protein (CP)

concentrations of 120 and 150 g kg-1 DM; dry matter digestibility (DMD) of 0.45 and

0.58; organic matter digestibility (OMD) of 0.50 and 0.64; neutral-detergent fibre

(NDF) concentrations of 370 and 290 g kg-1 DM; and acid-detergent fibre (ADF)

concentrations of 260 and 210 g kg-1 DM, respectively. Medicago sativa, grown under

similar conditions, had higher digestibility (0.63 DMD and 0.66 OMD) and similar CP

concentrations to D. rectum (140 g kg-1 DM), but higher concentrations of NDF and

Chapter 8: Cutting height, production and nutritive value of Dorycnium

166

ADF (410 and 290 g kg-1 DM). Leaf material from both Dorycnium species had a higher

nutritive value than edible stems, with DMD and OMD values of leaf of D. rectum

being 0.68 and 0.74, respectively. Uncut plants had a much lower nutritive value of

edible DM than the regrowth from cut treatments; older material was also of a lower

nutritive value. The relatively low nutritive value of even the young regrowth of

Dorycnium species suggests that forage quality is a major limitation to its use. Forage of

Dorycnium species could be saved for use during periods when other sources of forage

are in short supply, but infrequent grazing it is likely to produce forage of a low

nutritive value.

Introduction

Few perennial legumes, with the exception of Medicago sativa L. (lucerne), are well

adapted to the cropping regions of southern Australia. Thus, a range of new perennial

legumes that may provide options for controlling recharge of groundwater and slow the

onset of dryland salinity are currently under evaluation. An understanding of how

grazing should be managed is needed to optimise plant persistence, and pasture and

livestock productivity. Unless bred for grazing tolerance perennial pastures are likely to

need more intensive grazing management (Lodge 1991; Kemp and King 2001) than

traditional annual pastures systems, which are generally capable of persisting under set-

stocking regimes (Collins 1978). For instance, M. sativa pastures should be grazed

rotationally with an interval of approximately 6 weeks between grazing periods when

plants regrow and renew reserves in their crown (Lodge 1991). Frequent severe

defoliation of M. sativa pastures can cause plant death and thus a decline in sward

density and productivity (Lodge 1991). However, the applicability of this grazing

management to new perennial legume species is unknown and may be complicated by

differences in plant morphology. For example, M. sativa is herbaceous with the ability

to regrow from a subsurface crown where carbohydrate reserves are stored. Thus, M.

sativa is tolerant of relatively short periods of high severity grazing, providing reserves

are not overly depleted. However, many new species lie somewhere in the continuum

between woody and herbaceous (Chapter 1, Fig. 4), and hence all dry matter (DM) may

not be edible to livestock. New species may also differ from M. sativa in their allocation

of reserves and regrowth capability. Dorycnium hirsutum and D. rectum are

predominantly herbaceous, but accumulate woody stem at their base as they mature.

They are described as ‘sub-shrubs’ (Ball 1968). Dorycnium rectum has a more erect

167

growth habit than D. hirsutum and therefore the two species may accumulate DM and

respond to grazing differently.

For Dorycnium species, little is known about the management that minimises the

production of inedible DM, while enabling plants to regrow rapidly after grazing. In

New Zealand, two studies have investigated the effect of cutting management on the

DM production and yield components of D. rectum. Oppong et al. (2001) found that

cutting heights of 10, 80 and 120 cm had no subsequent effect on the yield of total DM

and edible DM of D. rectum. Douglas et al. (1996a) subjected D. rectum plants to 5

cutting regimes over summer and autumn (December–April) which differed in cutting

frequency (1, 2 or 3 cuts) and height (10 cm or 60 cm). Three cuts at 10 cm produced

the least edible DM (0.4 t DM ha-1) with two 60-cm cuts followed by one 10-cm cut

producing the highest edible DM (1.0 t DM ha-1). The edible component (leaf and soft

stem) was proportionately 0.33 of DM above the cutting height from cut treatments. In

both Oppong et al. (2001) and Douglas et al. (1996a), conservative cutting intensities

were used and the capacity of D. rectum to respond after severe defoliation was not

investigated. Dorycnium hirsutum is said to be tolerant of hard grazing (Sheppard and

Douglas 1986), but the response to different cutting or grazing managements has not

been investigated.

Because of the tolerance of Dorycnium species to drought (Wills 1983; Douglas et al.

1996b), it has been suggested that their role in grazing systems could be the provision of

standing green forage during times of shortage of forage (Chapter 2). Forage during

periods of low supply, such as the summer/autumn feed gap in Mediterranean climates,

has high economic value because it removes the need for high-cost supplementary

feeding to maintain livestock numbers (Bathgate and Pannell 2002; Flugge et al. 2004).

However, the nutritive value of Dorycnium forage during summer and autumn is low. In

Tasmania, Australia, Davies and Lane (2003) found that the dry matter digestibility

(DMD) values of D. hirsutum and D. rectum ranged from 0.58–0.49 and from 0.67–

0.47, respectively, peaking in November and declining steadily during summer. The

DMD values of Dorycnium forage declined below the level needed to maintain the

liveweight of ruminant livestock during this period (approximately a DMD value of

0.55). The DMD values of M. sativa forage were much higher during this period; 0.77

in September and 0.60 in February (Davies and Lane 2003). The crude protein (CP)


168

concentration was also much lower in Dorycnium species (130–180 g kg-1 DM,

declining to 50–60 g kg-1 DM in April) than in M. sativa (170 − 280 g kg-1 DM). The

organic matter digestibility (OMD, 0.874) and the CP concentration (200 g kg-1 DM) of

D. rectum leaf have been found to be much higher than edible stem (OMD of 0.456 and

75 g kg-1 DM) (Oppong et al. 2001). Thus, the ratio of leaf:stem and the selection of

these components will greatly influence the value of Dorycnium forage to ruminant

livestock. No studies have investigated the possibility of manipulating cutting or

grazing management of Dorycnium species to improve their nutritive value.

The current experiment investigated the effects of 5 cutting heights on the survival,

production and proportion of DM as leaf, edible stem and woody stem in D. hirsutum

and D. rectum over a growing season. Defoliation treatments were imposed at 8-week

intervals to mimic the recommended period between grazing for M. sativa and to assess

the response of Dorycnium species to similar regimes of grazing management.


Experimental design

The experiment was conducted at the Medina Research Station, Department of

Agriculture, Western Australia (32º 13’ S, 115º 47’ E, 14 m above sea level). Seedlings

were grown in a glasshouse in jiffy pots where they were inoculated with Rhizobium SU

343 for Lotus corniculatus. One 25 m long strip of D. hirsutum TAS 1002 and one 20 m

long strip of D. rectum SA 1231 seedlings were planted in August 2001 into white

plastic matting (to reduce weed competition). Strips consisted of two rows of plants at

30 cm intervals, with rows 50 cm apart and plant centres offset. A 1.2 m buffer between

strips of plastic was kept free from weeds. A basal application of 300 kg ha-1 of

superphosphate: potash (3:1) was applied at planting. Rainfall data is presented in Table

1. Approximately 25 mm of irrigation was also applied weekly throughout the

experiment.

Within the strips of each species, treatments were arranged in a randomised block

design with 6 replicates in D. rectum and 4 replicates in D. hirsutum. Individual plants

were allocated to different treatments in D. rectum, while in D. hirsutum individual

plants could not be separated and thus 0.5 × 0.5 m quadrats were used (the approximate

169

spread of each plant). The cutting height treatments are described in Table 2. Harvests

of herbage from above the cutting height of cut plants or quadrats were repeated at

approximately 8-week intervals. Sufficient plants or quadrats allocated to uncut

treatments were left uncut for destructive harvests at these times. Initial uncut DM

production was measured and cutting height treatments were imposed on 9 September

2002. Subsequent harvests were taken on 15 November 2002, 14 January 2003, 12

March 2003, 7 May 2003 and 1 July 2003.

Table 1. Monthly rainfall (mm) at Medina Research Station between September 2002 and June

2003. Additional irrigation of 25 mm was applied weekly.

2002 2003

Sept. Oct. Nov. Dec. Jan. Feb. Mar. Apr. May June

41 44 15 1 1 15 47 113 99 148

Table 2. The cutting height treatments imposed on Dorycnium rectum and D. hirsutum.

Cutting height Cutting height

treatment D. rectum D. hirsutum

Ground 0 cm or top

of crown

0 cm or top of

crown

Low 8 cm 5 cm

Mid 15 cm 10 cm

High 30 cm 15 cm

Uncut – –

A subsample of the cut herbage was separated into leaf, edible stem (approximately < 6

mm diameter) and woody stem (approximately > 6 mm diameter) components. Edible

stems were defined as stems that could be easily broken by hand. The herbage samples

were dried at 70ºC for three days and then weighed. The total DM production and the

proportion of leaf, edible stem and woody stem in each sample were estimated.

M. sativa cv. Sceptre was included as a reference species with which to compare the

nutritive value of the Dorycnium species. Seedlings were planted in June 2002 in an

adjacent strip with a similar design to the strips of the Dorycnium species. This plot was

managed in the same manner as the Dorycnium plots but cutting height treatments were

not imposed. Whole M. sativa shoots were cut at a height of 5 cm on the 21 January, 26


170

March, 7 May and 1 July 2003, dried at 70ºC for three days and included in the analyses

of nutritive value.

Estimated nutritive value

All dried samples were stored in a cool and dry environment until processing. Analyses

were not undertaken on woody stems as these would not be grazed by livestock. Two of

the six replicates of D. rectum were discarded to reduce the number of samples for

analysis. Leaf and edible stems of Dorycnium species were analysed from herbage

harvested from the mid-cutting treatment at each sampling date. In addition,

comparisons between cutting treatments were made for herbage sampled on 14 January

2003 and 7 May 2003.

Samples were ground to pass through a 1 mm screen using a cyclone grinder

(CYCLOTECH 1093 Sample Mill, Tecator, Hoganas, Sweden) and stored in plastic

vials at room temperature. Near infrared (NIR) spectra for each sample were collected

as log (1/R) over the whole NIR region from 1100 to 2500 nm with a scanning

monochromator (model 6500, NIRSystems Inc., Silver Spring, MD, USA). A subset of

80 samples were analysed for in vitro dry matter digestibility (DMD) using a

pepsin/cellulase assay (Clarke et al. 1982), ash (Faichney and White 1988), and neutral-

detergent fibre (NDF) and acid-detergent fibre (ADF) using the ANKOM filter-bag

method in accordance with the operating instructions, with CTAB instead of Cetavlon

(ANKOM Technology 1998). Organic matter digestibility (OMD) was calculated as the

digestibility of the combustible component of the sample (i.e. excluding ash content).

The samples were analysed for crude protein (CP) according to the method of Sweeney

(1989).

The data from the subset of 80 samples were analysed, using WinISI 2 Software

(WinISI, Infrasoft International, PA, USA), to produce prediction equations for feed

quality. The predicted values for the samples were compared to those from the

laboratory analysis to test the accuracy of the prediction equations. Samples with a low

correlation were removed and the remaining equations were used to estimate the

nutritive value of the remaining samples. The accuracy of the final prediction equations

for measurements of nutritive value are presented in Table 3.

171


Data were subjected to analysis of variance using Genstat 6.1 (GenStat 6 Committee

2002). All variables were found to follow a normal distribution. Cut treatments

(excluding uncut) were subjected to a repeated measures analysis because dry matter

production was measured on the same plants. Dry matter production and the proportions

of leaf, edible stem and woody stem were analysed for each species separately as

replication and the data units differed (i.e. g DM m-2 for D. hirsutum and g DM plant-1

for D. rectum). The main effects explored were time of harvest (with each harvest date

considered as independent) and cutting height treatment. Comparisons between main

effects were made using least significant differences or Tukey’s multiple comparisons

(P< 0.05).

Effects of species and harvest date on nutritive value variables were analysed for edible

forage components (i.e. leaf and stem) among D. hirsutum, D. rectum and M. sativa.

Between the two Dorycnium species, the main effects of edible forage components,

harvest date and cutting treatments were explored.

Table 3. Correlation coefficient (r2) between predicted values from near-infrared spectroscopy

and measured feed quality parameters and the number of samples on which equations were

based (n).

Variable r 2 n

Crude protein concentration 0.989 71

In vitro dry matter digestibility 0.918 79

Ash concentration 0.838 67

In vitro organic matter digestibility 0.910 68

Neutral-detergent fibre concentration 0.399 80

Acid-detergent fibre concentration 0.639 79

Results

Plant survival and DM production

The two Dorycnium species differed not only in growth habit but also in the nature of

regrowth (Figure 1). D. hirsutum regrew primarily from axillary buds on stems while in


172

D. rectum new shoots emerged mostly from the base of the plant in a manner similar to

M. sativa.

Figure 1. Comparison of growth habit (left) and the sites of regrowth (right) among (a)

Medicago sativa, (b) Dorycnium hirsutum and (c) D. rectum.

(a) M. sativa

(b) D. hirsutum

(c) D. rectum

UNCUT REGROWTH

173

Plant survival

In the treatment where the plants were cut to ground level, no regrowth of D. hirsutum

was measured at the third harvest (12 March 2003). One ground-cut quadrat produced

some DM yield at the harvest on 7 May 2003 but, thereafter, all plants on this treatment

had died. D. hirsutum plants in one low-cut quadrat had also died by 1 July 2003. For D.

rectum, all ground-cut plants failed to regrow after the harvest on 7 May 2003.

Effect of cutting height on total production and components of DM

For both D. hirsutum and D. rectum, cutting height treatments affected total DM

production (Tables 4 and 5). Plants subjected to lower cutting heights displayed less

regrowth but this trend was less pronounced in D. rectum than D. hirsutum. Dry matter

production declined in all cutting treatments during the experiment. The majority of DM

harvested above the cutting height of all cutting treatments in both species was

considered edible, with negligible woody stem present (Figure 2). Differences between

species in the proportion of edible DM made up by leaf and stem were evident. On

average, the proportion of DM consisting of leaf in D. hirsutum was 0.72 compared to

0.56 in D. rectum. Cutting treatments and harvest date also affected the proportion of

leaf and stem in both species. In both D. hirsutum and D. rectum, growth from ground-

cut plants had a lower proportion of leaf than the other cutting treatments (0.67 and

0.53, respectively). Plants cut at a greater height had a higher proportion of leaf (0.61)

than low- or mid-cut plants of D. rectum. Regrowth harvested on 1 July 2003 had a

higher proportion of leaf than the previous harvests in both species, although little DM

was produced at this time (Tables 4 and 5).

Total production and DM components from uncut plants

Uncut D. hirsutum quadrats continued to accumulate DM over the experiment but DM

production was less during autumn (12 March–1 July 2003) than in spring and summer

(Table 6). Growth of uncut D. rectum plants was confounded by large variation in plant

size which resulted in variable DM measurements. In both species, the proportion of

woody stem in the DM of uncut plants increased during the experiment, peaking at 0.69

at the last harvest on 1 July 2003. This accumulation of woody stem resulted in a

decline in the proportion of edible DM (Table 6).


174

Table 4. Dry matter production above cutting height (g DM m-2) of D. hirsutum plants

subjected to 4 cutting heights over 1 growing season. Statistical level of significance and least

significant difference at P< 0.05 (l.s.d) are also presented.

Cutting height above ground Date of harvest Ground

(0 cm)

Low

(5 cm)

Mid

(10 cm)

High

(15 cm) Mean

15 Nov. 2002 105 220 279 337 235

4 Jan. 2003 41 212 290 320 216

12 March 2003 0 119 188 251 140

7 May 2003 15 77 142 131 91

1 July 2003 0 7 14 16 9

Mean 32 127 183 211 138

Effects Level of significance l.s.d.

Treatment *** 8.4

Date *** 9.2

Treatment × date *** 16.9 ***, P< 0.001

Table 5 Dry matter production above cutting height (g DM plant-1) of D. rectum subjected to 4

cutting heights over 1 growing season. Statistical level of significance and least significant

difference at P< 0.05 (l.s.d) for each effect are also presented.

Cutting height Date of harvest Ground

(0 cm)

Low

(8 cm)

Mid

(15 cm)

High

(30 cm) Mean

15 Nov. 2002 43.8 53.1 61.0 54.2 53.0

4 Jan. 2003 25.0 33.0 39.5 28.5 31.5

12 March 2003 5.6 19.5 27.5 25.1 19.4

7 May 2003 2.1 22.2 36.3 56.6 29.3

1 July 2003 0.0 1.7 4.5 15.5 5.4

Mean 15.3 25.9 33.8 36.0 27.7

Effects Level of significance l.s.d.

Treatment n.s. 28.4

Date *** 10.0

Treatment × date n.s. 32.6 ***, P< 0.001; n.s., not significant

175

Figure 2. Proportion of DM harvested above cutting height which consisted of leaf (grey

shading), edible stem (clear) and woody stem (black shading) under 4 cutting height treatments

for (a) D. hirsutum and (b) D. rectum over 1 growing season. Ground-, low-, mid- and high-

cutting height treatments used were 0, 5, 10 and 15 cm in D. hirsutum and 0, 8, 15 and 30 cm in

D. rectum.

(a) D. hirsutum

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

15 N

ov 0

214

Jan

03

12 M

ar 0

37

May

03

1 Ju

l 03

15 N

ov 0

214

Jan

03

12 M

ar 0

37

May

03

1 Ju

l 03

15 N

ov 0

214

Jan

03

12 M

ar 0

37

May

03

1 Ju

l 03

15 N

ov 0

214

Jan

03

12 M

ar 0

37

May

03

1 Ju

l 03

Ground Low Mid High

Pro

porti

on o

f bio

mas

s

(b) D. rectum

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

15 N

ov 0

214

Jan

03

12 M

ar 0

37

May

03

1 Ju

l 03

15 N

ov 0

214

Jan

03

12 M

ar 0

37

May

03

1 Ju

l 03

15 N

ov 0

214

Jan

03

12 M

ar 0

37

May

03

1 Ju

l 03

15 N

ov 0

214

Jan

03

12 M

ar 0

37

May

03

1 Ju

l 03

Ground Low Mid High

Pro

porti

on o

f bio

mas

s

Table 6. Dry matter (DM) production at each harvest, and its components, for uncut D. rectum and D. hirsutum plants over 1 growing season. Letters denote

significant differences (P< 0.05) between dates.

D. hirsutum D. rectum

Date of sampling DM production

(kg m-2)

Proportion of leaf

Proportion of edible

stem

Proportion of woody stem

DM production (g/plant)

Proportion of leaf

Proportion of edible stem

Proportion of woody stem

8 Sept. 2002 1.20a 0.298a 0.396ab 0.306 a 96a 0.252a – –

15 Nov. 2002 1.62a 0.218ab 0.467a 0.315 a 375ab 0.226ab 0.406a 0.368a

14 Jan. 2003 2.31ab 0.215ab 0.350b 0.436ab 360ab 0.187bc 0.326ab 0.488a

12 Mar. 2003 3.54bc 0.175b 0.220c 0.611bc 236a 0.097d 0.252bc 0.650b

7 May 2003 3.62bc 0.169b 0.239c 0.587bc 927c 0.158cd 0.194cd 0.649b

1 July 2003 3.84c 0.146b 0.163c 0.691c 790bc 0.146cd 0.164cd 0.690b

.

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Estimated nutritive value

Comparisons between species at mid-cutting height regime

D. hirsutum, D. rectum and M. sativa differed for all nutritive value variables (Table 7).

Forage from M. sativa had higher DMD and OMD values than both Dorycnium species,

despite possessing higher NDF and ADF concentrations. CP and ash concentrations

were higher in D. rectum than M. sativa or D. hirsutum. Differences during summer and

autumn were found for CP concentration, which was higher for D. rectum and M. sativa

in May, and NDF and ADF concentrations, which increased in all species in May.

There were large differences in all nutritive value variables between leaf and edible

stem from mid-cut plants (Table 8). In D. rectum, the nutritive value of leaf was far

superior to that of stem. Leaf of D. rectum had higher CP and ash concentrations, higher

DMD and OMD values, and lower NDF and ADF concentrations than the leaf of D.

hirsutum. In D. hirsutum, although the nutritive value of leaf was higher than stem, this

difference was not as large as in D. rectum (Table 8). Leaf of D. rectum had a higher

nutritive value than that of D. hirsutum with a DMD value of 0.63 and an OMD value of

0.71, similar to that of the shoot (leaf and stem) of M. sativa (Tables 7 and 8). However,

the higher proportion of lower quality edible stem in D. rectum meant that total edible

DM had lower DMD and OMD values than M. sativa.

Cutting effects on nutritive value

Cutting treatments affected all nutritive value variables in both Dorycnium species

(Table 9). Edible DM from uncut plants had a lower CP concentration and lower DMD

and OMD values than that of cut treatments in both species. Uncut plants had higher

NDF and ADF concentrations in D. hirsutum and lower concentrations of ash in D.

rectum. Within each species, differences in nutritive value between cutting heights were

small, except for D. rectum where ground-cut plants had higher NDF and ADF

concentrations and high-cut plants had lower NDF and ADF concentrations than other

cutting heights.

Table 7. Comparison of D. hirsutum, D. rectum and M. sativa forage (leaf + edible stem) for feed quality from mid-cut plants (10 cm in D. hirsutum, 15 cm in D.

rectum and 5 cm in M. sativa) over summer and autumn. Feed quality measurements are crude protein (CP) concentration, dry matter digestibility (DMD), ash

concentration, organic matter digestibility (OMD) and neutral-detergent fibre (NDF) and acid-detergent fibre (ADF) concentrations. Statistical levels of significance

for each effect are presented.

Species Date CP (g kg-1 DM)

DMD

Ash (g kg-1 DM)

OMD

NDF (g kg-1 DM)

ADF (g kg-1 DM)

13 Jan. 2003 118 0.458 64 0.500 362 245 13 Mar. 2003 114 0.449 71 0.493 360 244

7 May 2003 120 0.456 62 0.493 392 288

D. hirsutum

Mean 117 0.454 66 0.495 371 259 13 Jan. 2003 131 0.567 89 0.635 255 163

13 Mar. 2003 139 0.559 98 0.627 297 190 7 May 2003 173 0.604 104 0.664 323 266

D. rectum

Mean 148 0.577 97 0.642 291 206 13 Jan. 2003 129 0.660 88 0.678 383 276

13 Mar. 2003 123 0.625 65 0.640 415 286 7 May 2003 155 0.610 69 0.656 431 300

M. sativa

Mean 136 0.631 74 0.658 410 287 Effects Level of significance Species *** *** *** *** *** *** Date *** n.s. n.s. n.s. *** *** Species × date n.s. n.s. *** n.s. n.s. n.s. *** = P< 0.001, n.s., not significant

Table 8. Nutritive value of edible stem and leaf of D. hirsutum and D. rectum harvested from mid-cut plants (10 cm in D. hirsutum, 15 cm in D. rectum) at

approximately 8-week intervals over summer. Nutritive value variables are crude protein (CP) concentration, dry matter digestibility (DMD), ash concentration,

organic matter digestibility (OMD), and neutral-detergent fibre (NDF) and acid-detergent fibre (ADF) concentrations. Statistical levels of significance are presented.

“Herbage” effect refers to comparisons between leaf and stem.

CP (g kg-1 DM)

DMD

Ash (g kg-1 DM)

OMD

NDF (g kg-1 DM)

ADF (g kg-1 DM)

Species Date

Leaf Stem Leaf Stem Leaf Stem Leaf Stem Leaf Stem Leaf Stem 5 Nov. 2002 136 103 0.423 0.363 6.5 6.6 0.456 0.414 379 544 332 417 14 Jan. 2003 129 85 0.487 0.370 6.6 5.7 0.528 0.416 308 522 195 394

12 Mar. 2003 124 85 0.480 0.357 7.4 6.2 0.525 0.396 301 537 187 414 7 May 2003 132 83 0.488 0.359 6.5 5.5 0.526 0.394 345 532 248 406

D. hirsutum

Mean 130 89 0.469 0.362 6.7 6.0 0.509 0.405 333 534 240 408

5 Nov. 2002 162 68 0.605 0.388 11.5 7.6 0.684 0.443 230 498 180 360 14 Jan. 2003 188 108 0.627 0.389 10.4 4.6 0.718 0.387 238 488 94 366

12 Mar. 2003 153 65 0.625 0.363 11.2 5.7 0.708 0.387 176 499 128 375 7 May 2003 198 96 0.679 0.380 11.3 7.4 0.740 0.437 260 510 227 383

D. rectum

Mean 175 84 0.634 0.380 11.1 6.3 0.713 0.413 226 499 157 371 Effects Level of significance Species *** *** *** *** *** *** Herbage *** *** *** *** *** *** Date *** ** *** n.s. *** *** Species × herbage *** *** *** *** *** ** Species × date *** n.s. *** n.s. n.s. ** Herbage × date n.s. *** ** *** ** *** Species × herbage × date n.s. n.s. n.s. n.s. n.s. n.s.

***, P< 0.001; **, P< 0.01; n.s., not significant

Table 9. Comparison between nutritive value of D. hirsutum and D. rectum subjected to different cutting heights. Measurements are the means from all harvest dates

for crude protein (CP) concentration, dry matter digestibility (DMD), ash concentration, organic matter digestibility (OMD), and neutral-detergent fibre (NDF) and

acid-detergent fibre (ADF) concentrations. Statistical levels of significance for each effect are presented.

Species Cutting height

CP (g kg-1 DM)

DMD

Ash (g kg-1 DM)

OMD

NDF (g kg-1 DM)

ADF (g kg-1 DM)

Ground 110 0.453 61 0.475 389 286 Low 124 0.481 64 0.519 364 248 Mid 118 0.455 63 0.495 379 268 High 119 0.474 62 0.512 376 262

D. hirsutum

Uncut 85 0.358 62 0.398 494 367 Ground 128 0.526 99 0.592 393 270 Low 131 0.530 96 0.604 364 256 Mid 126 0.511 84 0.561 352 262 High 135 0.523 81 0.578 304 196

D. rectum

Uncut 99 0.447 67 0.470 371 285 Effects Significance Species *** *** *** *** *** *** Treatment *** *** *** *** *** *** Species × treatment n.s. n.s. *** n.s. *** *** ***, P< 0.001; n.s., not significant

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Discussion

Cutting treatments imposed on Dorycnium species in this study were intended to be

indicative of varying severity of grazing. Cutting does not accurately reproduce the

removal of DM by grazing because choice of forage components by ruminants is not

considered. In this case, it appears that the cutting heights combined with the frequency

of cutting were probably too intensive for Dorycnium species. Nonetheless, the cutting

treatments did differentially affect plant survival, DM production and its components,

and the nutritive value of the edible DM, of Dorycnium species.

Total DM production and plant survival

In both Dorycnium species, plants cut to a lower height displayed a reduced capacity for

regrowth. This was not unexpected; more leaf material in plants cut at greater height

allowed photosynthesis and plant growth to be maintained without having to produce

more leaf. In D. hirsutum, because regrowth occurs by axillary branching, the removal

of growing points in plants cut to a lower height may have also reduced regrowth. It is

unclear whether the decline in DM production observed in all cut treatments in both

species during the experiment is indicative of the seasonal growth pattern of these

species or removal of growing points and declining plant reserves. Evidence for the

former explanation is found in the growth of uncut plants being also observed to be

slow during early autumn (March to May).

Despite having the ability to regrow from woody stems, repeated cutting at a low height

of D. hirsutum (i.e. ground and low treatments) resulted in plant death, presumably due

to depletion of plant reserves or removal of growing points. Ground-cut plants of D.

hirsutum, where all woody material was removed, failed to regrow after the second

harvest. This suggests that D. hirsutum does not accumulate carbohydrate reserves in its

roots, unlike M. sativa where this occurs in a sub-surface crown. The accumulation of

carbohydrate reserves in the perennial legume Lotus corniculatus also differs from M.

sativa and grazing management that maintains leaf area is necessary to maximise

growth (Nelson and Smith 1968). Similar grazing management appears to be required

for D. hirsutum. D. rectum showed greater tolerance of cutting to ground level and

regrew well after two to three harvests on this treatment. However, repeated cutting to

ground level at 8-week intervals also eventually resulted in plant death. Shading by


182

adjacent plants may also have contributed to declining plant health in D. rectum plants

cut to ground level. Nonetheless, the decline in DM production of all cut plants and the

eventual death of some plants subjected to lower cutting heights, suggests an 8-week

interval between severe defoliation is too short for Dorycnium species.

A proposed role in farming systems for Dorycnium is as a standing ‘haystack’, to

provide forage during periods of low feed supply (Wills 1983; Douglas et al. 1996b)

which occur in late summer and autumn in southern Australia (Chapter 1). This

experiment suggests that Dorycnium plants can accumulate a large amount of inedible

woody biomass during spring and summer if left uncut. Although uncut plants produced

more DM than cut treatments, edible DM production was similar (e.g. for D. hirsutum,

uncut plants had accumulated 644 g edible DM m-2 at its peak on 7 May, while to this

date the cumulative edible DM production, averaged over all cut treatments, was 682 g

DM m-2). In New Zealand, studies suggest that plant death can occur in Dorycnium

species under lax grazing management (Wills 1983). Plants carrying large amounts of

leaf into summer have also died in Western Australia. Thus, more tactical grazing to

reduce the development of woody stems is desirable. Evidence from this experiment

suggests more than 8 weeks between grazing events is required and that grazing

management used for M. sativa is not suitable for Dorycnium species. However, if

longer periods are required, a greater proportion of biomass may become woody. At this

stage it seems that grazing in late spring may be beneficial to avoid lignification of

stems, to reduce plant leaf area and to encourage fresh growth.

Nutritive value

This experiment supports previous evidence that forage quality is a major limitation to

the development of Dorycnium species as forage plants. Davies and Lane (2003)

reported lower digestibility of forage from Dorycnium species than for M. sativa.

However, the DMD of fresh growth of both species in the present experiment is

considerably lower than peak values documented by Davies and Lane (2003) (< 0.46

compared to 0.58 for D. hirsutum and < 0.60 compared to 0.67 for D. rectum). The

reasons for these differences are not clear but it is likely that methodological,

environmental and perhaps genetic differences played some part. In the present

experiment, the DMD of the leaf fraction of fresh growth in D. hirsutum was below a

DMD value of 0.55, which is generally considered necessary for maintenance of live

weight of ruminant livestock (Freer et al. 1997). This is a major issue to be overcome

183

for D. hirsutum. In this experiment only 1 accession of each Dorycnium species was

tested. Variation in forage quality may exist and improvements may be possible through

breeding.

The reasons for the low DMD of Dorycnium species are not clear. Notable in the

present experiment were the higher concentrations of ADF and NDF measured in M.

sativa forage than in the Dorycnium species (Table 7). The concentration of ADF in

most forages is a good predictor of in vivo digestibility (Marten, 1981). In M. sativa, the

fibre components of the forage account for much of the indigestible organic material,

while in both Dorycnium species there is a larger discrepancy between the OMD and

ADF concentration. High levels of condensed tannins (CT) (> 0.12 of DM) have been

documented in Dorycnium species and may be responsible for the lower DMD (Terrill

et al. 1992; Waghorn and Molan 2001). The removal of the effects of CT in D. rectum

(by the addition of polyethylene glycol) has been shown to increase DMD from 0.6 to

0.64 and nitrogen digestibility from 0.24 to 0.74 (Waghorn and Molan 2001). CT were

not measured in this experiment, but have been documented in the accessions used

(Lane et al. 2004). CT bind to protein, and high levels in Dorycnium forage may have

rendered this fraction indigestible. The effect of CT on in vitro measures of digestibility

are not well understood and may have interfered with the DMD assay by binding to

proteins or enzymes and thus causing the assay to underestimate in vivo digestibility.

As expected, nutritive value of leaf in both Dorycnium species was higher than that of

stem. Leaf of D. rectum had a high CP concentration (150–200 g kg-1 DM) and was

highly digestible (> 0.70 OMD). However, the high proportion of stem (approximately

0.55 of DM) in D. rectum meant that the nutritive value of all edible DM in D. rectum

was much lower. Leaf of D. rectum had an OMD which was 0.20 higher than that of D.

hirsutum. Higher concentrations of ADF in D. hirsutum leaves would have contributed

to these differences but do not fully explain them. Waghorn et al. (1998) found CT

concentration to be much higher in the leaves of D. rectum than in the stems.

Differences in CT concentrations between species may have caused the lower DMD of

D. hirsutum leaf. Despite the low nutritive value found for edible DM in Dorycnium

species, the higher nutritive value of leaf of D. rectum, if selected preferentially by

livestock, would result in a higher nutritive value of Dorycnium forage for grazing.


184

However, no observations have been made of the grazing behaviour of animals grazing

Dorycnium forage.

Conclusions and practical implications

This experiment demonstrates that D. rectum has displayed the ability to regrow after

mechanical removal of inedible woody material to ground level. Such removal could

prove valuable in D. rectum after a grazing event to remove inedible biomass and

encourage regrowth with a higher nutritive value. D. rectum could be managed in a

similar way to tagasaste (Chamaecytisus proliferus Link.), a forage shrub grown in

alleys and regularly coppiced to encourage fresh growth and prevent it reaching

unmanageable heights (Wiley 2001). Coppicing of tagasaste requires specialised

equipment; the ‘shrubbier’ D. rectum may have the advantage that it could be cut easily

with a tractor-mounted slasher.

In southern Australia, M. sativa pastures extend the period that green forage is available

beyond that of annual pastures by providing forage in spring, early summer and after the

first rains in autumn (Dear et al. 2003). M. sativa also provides valuable forage by

making use of out-of-season rainfall during summer and early autumn ((Dear et al.

2003). However, M. sativa forage is unreliable during this period in climates where

rainfall at this time is infrequent. Previous studies have identified that Dorycnium

species, in particular D. hirsutum, are drought-tolerant and could be used as forage to

reduce the need for supplementary feeding when other pasture sources are not available

(Wills 1983; Waghorn et al. 1998; Davies and Lane 2003). If used in this manner, the

low nutritive value of Dorycnium species is less of a limitation, as few or no high

quality forage options are available during summer and early autumn. However, if

plants are left to grow during the spring and summer, a large proportion of inedible DM

is produced and the quality of edible forage declines further (DMD value of < 0.50).

Furthermore, this experiment was conducted under favourable conditions, where plants

were supplied with irrigation over summer. In field conditions, leaf drop due to drought

and harsher growing conditions are likely to produce forage of even lower value.

Other pasture systems used to provide forage during late summer and autumn currently

have distinct advantages over Dorycnium. For example, saltbush (Atriplex spp.) is

currently grown on salt-affected land in southern Australia and has forage with similar

185

concentrations of CP (100–150 g kg-1 DM ) and DMD (0.50–0.60) to Dorycnium

species (Norman 2002). Saltbush grown on saline land acquires high levels of salt,

which restricts forage intake by livestock. However, when supplemented with low-cost

straw, animal production is improved (Barrett-Lennard 2003). Saltbush is popular

because it uses otherwise unproductive land to provide an economic benefit by enabling

higher carrying capacity and livestock condition to be maintained during summer.

However, with further selection for improved forage quality and a better understanding

of grazing management, Dorycnium species could be a useful niche forage crop to

provide other benefits for livestock production systems and reduce groundwater

recharge on non-salt affected areas of the landscape.

References

ANKOM Technology (1998) 'Method for determining acid detergent fibre.' (ANKOM Technology Corporation Publication: Fairport, USA) Ball PW (1968) Dorycnium Miller. In 'Flora Europaea'. (Eds TG Tutin, VH Heynood, NA Burgess, DM Moore, DH Valentine, SM Walters, DA Webb) pp. 172. (Cambridge University Press: London) Barrett-Lennard EG (2003) 'Saltland Pastures in Australia - A practical guide.' (Land, Water and Wool Sustainable Grazing on Saline Lands Sub-program) Bathgate A, Pannell DJ (2002) Economics of deep-rooted perennials in western Australia. Agricultural Water Management 53, 117-132. Clarke T, Flinn PC, McGowan AA (1982) Low-cost pepsin-cellulase assays for prediction of digestibility of herbage. Grass and Forage Science 37, 147-150. Collins WJ (1978) The effect of defoliation on inflorescence production, seed yield and hardseededness in swards of subterranean clover. Australian Journal of Agricultural Research 29, 789-801. Davies SR, Lane PA (2003) Seasonal changes in feed quality of Dorycnium spp. In 'Proceedings of the 11th Australian Agronomy Conference'. Geelong, Victoria. (Eds M Unkovich, GJ O'Leary). (The Australian Society of Agronomy Inc. Victorian Institute for Dryland Agriculture) Dear BS, Moore GA, Hughes SJ (2003) Adaptation and potential contribution of temperate perennial legumes to the southern Australian wheatbelt: a review. Australian Journal of Experimental Agriculture 43, 1-18. Douglas GB, Bulloch BT, Foote AG (1996a) Cutting management of willows (Salix spp.) and leguminous shrubs for forage during summer. New Zealand Journal of Agricultural Research 39, 175-184.


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Douglas GB, Wills BJ, Pryor HN, Foote AG, Trainor KD (1996b) Establishment of perennial legume species in drought-prone, North and South Island sites. Proceedings of the New Zealand Grassland Association 58, 253-257. Faichney GJ, White GA (1988) Partition of organic-matter, fibre and protein digestion in ewes fed at a constant rate throughout gestation. Australian Journal of Agricultural Research 39, 493-504. Flugge F, Abadi A, Dolling PJ (2004) Lucerne-based pasture for the central wheat-belt region of Western Australia - a whole-farm economic analysis. In 'Proceedings of the "Salinity Solutions" conference'. Bendigo, Victoria Freer M, Moore AD, Donnelly JR (1997) GRAZPLAN: Decision support systems for Australian enterprises - II. The animal biology model for feed intake, production and reproduction. Agricultural Systems 54, 77-126. GenStat 6 Committee (2002) GenStat 6th Edition 6.1.0.200. Lawes Agricultural Trust, Rothampsted, UK. Kemp DR, King WM (2001) Plant competition in pastures - implications for management. In 'Competition and Succession in Pastures'. (Eds PG Tow, A Lazenby) pp. 85-102. (CABI Publishing: Oxon, UK) Lane PA, Davies SR, Hall EJ, Moore GA (2004) 'Dorycnium species as alternative forage plants.' Rural Industries Research and Development Corporation, Report No. 04/159. Lodge GM (1991) Management practices and other factors contributing to the decline in persistence of grazed lucerne in temperate Australia: a review. Australian Journal of Experimental Agriculture 31, 713-724. Martin GC (1981) Chemical, in vitro and nylon bag procedures for evaluating forage in the USA. In ‘Forage Evaluation: Concepts and Techniques’. (Eds JL Wheeler, RD Mochrie) pp. 39-55. (CSIRO Publishing: East Melbourne, Australia) Nelson CJ, Smith D (1968) Growth of birdsfoot trefoil and alfalfa. III. Changes in carbohydrate reserves and growth analysis under field conditions. Crop Science 8, 25-28. Norman HC (2002) Nutritive value of plants growing on saline land. In '8th National Conference and Workshop on the Productive Use and Rehabilitation of Saline Lands (PURSL)'. Fremantle pp. 59-70. (Promaco Conventions Pty Ltd) Oppong SK, Kemp PD, Douglas GB, Foote AG (2001) Browse yield and nutritive value of two Salix species and Dorycnium rectum in New Zealand. Agroforestry Systems 51, 11-21. Sheppard JS, Douglas GB (1986) Management and uses of Dorycnium spp. Water and Soil Miscellaneous Publication 94, 260-262.

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Sweeney RA (1989) Generic combustion method for determination of crude proteins in feeds: collaborative study. Journal of the Association of Official Analytical Chemists 72, 770-774. Terrill TH, Rowan AM, Douglas GD, Barry TN (1992) Determination of extractable and bound condensed tannin concentrations in forage plants, protein concentrate meals and cereal grains. Journal of the Science of Food and Agriculture 58, 321-329. Waghorn GC, Douglas GB, Niezen JH, McNabb WC, Foote AG (1998) Forages with condensed tannins - their management and nutritive value for ruminants. Proceedings of the New Zealand Grassland Association 60, 89-98. Waghorn GC, Molan AL (2001) Effect of condensed tannins in Dorycnium rectum on its nutritive value and on the development of sheep parasite larvae. Proceedings of the New Zealand Grassland Association 63, 273-277. Wiley T (2001) Tagasaste (Fodder Shrub). In 'Good Food Guide for Sheep'. (Eds K Crocker, P Watt). (Department of Agriculture, Western Australia: Perth) Wills BJ (1983) 'Forage plants for the semi-arid high country and rangelands of New Zealand.' (Centre of Resource Management, Lincoln College, Special Publication 26, Canterbury, New Zealand).

Chapter 9: General discussion

Introduction

Dryland salinity is a major environmental constraint facing Australian agriculture. Our

challenge is to develop technologies that deal with the unused excess water resulting

from current agricultural production systems. There is potential to use this extra water to

enhance production. Perennial forages that increase water use enable agricultural

production to continue with little disruption, and are broadly applicable to a range of

systems and environments in southern Australia (Chapter 1). However, the majority of

commercially available perennial forages are best suited to high rainfall environments.

Lucerne (Medicago sativa) is the most widely adapted species and is sown in lower

rainfall climatic zones, but its range is currently limited by soil acidity, waterlogging

and low summer rainfall (Cocks 2001; Humphries and Auricht 2001). Thus, a wide

range of perennial forages that can fill these niches and provide diversity, is needed. The

major aim of this PhD research was to investigate agronomic traits of several species of

the genus Dorycnium and thereby improve our understanding of where they might be

best used in Australia and how they might be best integrated into agricultural systems

for the management of dryland salinity.

Potential ecological scope for Dorycnium

Dorycnium species do appear to have potential in the temperate pasture regions of

southern Australia. Climate matching suggests that D. hirsutum and D. rectum, in

particular, originate from regions with the most similar climatic conditions to southern

Australia (Chapter 3). Despite the similarity in the predicted zones of climate adaptation

between these two species, survival of D. hirsutum seedlings over summer (> 50%) was

superior to D. rectum (< 20%) in a range of environments in south-west Western

Australia (Chapter 5). The dissimilar root morphology (Chapter 6) and physiological

responses to water deficit (Chapter 7) found in the D. hirsutum and D. rectum

accessions tested may explain their different ability to survive in these environments.

These findings imply that the two species occupy different ecological niches, despite

their similar distribution. There is some indication in the literature that D. rectum mostly

occurs in moist sites or near sources of water (Demiriz 1970); such a restriction would

explain its inability to handle long periods of water-stress. Reliable establishment of D.


190

rectum seems unlikely in low rainfall environments of southern Australia (Chapter 5)

and D. rectum is probably better adapted to higher rainfall zones or situations where

water is more readily available. The ecological niche where D. rectum might best fit

remains uncertain, but when provided with suitable conditions this species can be

particularly productive (Douglas and Foote 1994) and thus warrants further evaluation.

Previous studies have documented the tolerance of D. hirsutum to drought and stressful

environmental conditions (Wills 1983; Sheppard and Douglas 1986; Douglas et al.

1996b; Lane et al. 2004). In the current project, D. hirsutum displayed similar

adaptations to drought to M. sativa. The ability of D. hirsutum to produce a deep root

system and extract water from soil depths equivalent to M. sativa was demonstrated in

Chapter 4. Seedlings of the same size of D. hirsutum and M. sativa also produced roots

to equivalent depths (Chapter 6) and their physiological responses to increasing water

deficit were also similar (Chapter 7). These qualities, and the survival of D. hirsutum at

Merredin in the low rainfall wheat-belt of Western Australia (Chapters 4 and 5) indicate

that this species may be at least as tolerant of these environments as M. sativa.

D. hirsutum also possesses other characteristics consistent with plants adapted to

challenging conditions. Leaf movements to reduce incident radiation were observed in

plants as water deficit developed (Chapter 7). The highly pubescent (hairy) leaves of D.

hirsutum could also reduce water loss by decreasing the conductance of water through

the boundary layer of the leaf and increasing the reflection of radiation (Karabourniotis

et al. 1995), thereby decreasing leaf temperature (Ehleringer 1984). Leaf pubescence

along with the accumulation of secondary compounds (e.g. tannins) may also provide

protection from leaf herbivory (Coley et al. 1985). Such characteristics are common in

slow-growing species and are thought to increase leaf longevity and reduce leaf

turnover and nutrient loss (Coley et al. 1985). The investment of resources in these

structures and secondary compounds produces leaves of lower specific leaf area (i.e.

leaf area per unit mass), which often explains the slower growth rates of plants adapted

to stressful environments (Lambers and Poorter 1992). In Chapter 6, the relative growth

rate of D. hirsutum was lower than M. sativa due to its lower specific leaf area.

Furthermore, in Chapter 7, water-stressed D. hirsutum possessed leaves with lower

specific leaf area than well watered plants, which suggests that D. hirsutum might also

alter leaf morphology in response to stress. These adaptations provide further evidence

191

that D. hirsutum is a species with potential for the more difficult environments in the

agricultural regions of southern Australia.

In addition to adaptations to overcome water deficit, current evidence in the literature

suggests that D. hirsutum could be better suited to acid soils than M. sativa (Chapter 2).

Soil acidity is the major limitation to the distribution of current M. sativa cultivars in

southern Australia (Humphries and Auricht 2001). Although no direct comparisons of

acid soil tolerance have been made between D. hirsutum and M. sativa, D. hirsutum has

a tolerance of aluminium similar to that of other pasture species known to be more

tolerant than M. sativa (Edmeades et al. 1991b;1991a; Schachtman and Kelman 1991;

Wheeler and Dodd 1995). However, the tolerances of a range of stresses associated with

soil acidity, other than aluminium, have not been documented for Dorycnium. In

particular, acid tolerance of root nodule bacteria is a major limitation of other legumes

that has not been investigated in Dorycnium (Howieson and Ballard 2004). Despite the

need for further evaluation of the acid soil tolerance of Dorycnium species, the likely

tolerance of aluminium along with drought tolerance traits suggest that D. hirsutum may

have potential in low rainfall environments on acid soils; a niche in southern Australia

where no perennial legumes are currently suited.

In conclusion, the capacity of D. hirsutum to use similar amounts of water to M. sativa

at Merredin (Chapter 4) indicates that there is a significant opportunity for it to play a

role in dryland salinity management in these regions, where there is currently a shortage

of perennial legumes options. Despite the potential of Dorycnium, it will not be a

replacement for currently commercial pasture species. The role of Dorycnium species

will be in currently unfilled niches, either as perennial forages in regions where the

performance of other species is poor, or as more specialised forages to meet specific

needs, such as to improve feed continuity or provide animal health benefits (discussed

later).

Matching Dorycnium with farming systems

The different climatic regions to which D. hirsutum and D. rectum are best adapted will

greatly influence the predominant production enterprise and thus the farming systems in

which they each will need to fit. For example, D. rectum will probably be best suited to

high rainfall environments where a higher proportion of the enterprise involves


192

livestock grazing on pastures. Thus, D. rectum requires attributes that allow its use in

permanent pastures (e.g. long-lived and persistent under grazing). D. rectum would not

suit traditional herbaceous pasture swards because of its erect habit and semi-

herbaceous form; it can grow to heights > 1.5 m and accumulates a significant

proportion of woody stem (Chapter 8). Alley systems, similar to those used for forage

shrubs like tagasaste (Chamaecytisus proliferus) (Wiley 2000a) or leucaena (Leucaeana

leucocephala) (Kang and Gutteridge 1994), would enable D. rectum to be managed

somewhat independently from a sward of herbaceous annual or perennial pastures

growing in the inter-row. D. hirsutum, on the other hand, appears best suited to low

rainfall environments. As these are regions where crop production dominates and

permanent pastures are rare, D. hirsutum will need to be integrated into cropping

systems or survive in situations where cropping is not profitable. The replacement of

annual ley rotations with phase systems (i.e. multiple years of pasture) may better allow

the incorporation of perennial forages during the pasture phase (Reeves and Ewing

1993; Ridley et al. 1998).

In addition to production enterprise considerations, this study has confirmed a number

of factors that might limit the potential farming systems in which Dorycnium could be

used. Low seedling vigour is a major inadequacy of Dorycnium species (Chapters 5 and

6). For D. rectum, this may not be overly problematic. Providing plants are sufficiently

long-lived, higher cost establishment via planting of seedlings or strip seeding, as used

for other forage shrubs such as tagasaste or saltbush (Atriplex spp.)(Wiley 2000b;

Barrett-Lennard 2003), might be feasible in permanent pastures. However, slow

establishment could limit the use of D. hirsutum in the short-phase rotations with crops

(i.e. < 4 years) already used for M. sativa. Competition from weeds seems to reduce D.

hirsutum establishment reliability (Chapter 5) and a number of establishment years are

recommended before grazing can commence (Wills 1983; Sheppard and Douglas 1984).

Longer-term rotations, which spread the costs of establishment over a longer period,

provide one opportunity for D. hirsutum. However, the Dorycnium pasture phase would

need to create a sufficiently large soil water buffer to store drainage for a number of

years during the cropping phase. This might be possible in low rainfall environments

where a soil buffer of 70 mm prevents drainage to the watertable for 5 years, on

average, and even up to 12 years, depending on rainfall conditions (Ward et al. 2003). A

larger buffer of 120 mm in these environments would prevent drainage for 8 years on

193

average (Ward et al. 2003). The results presented in Chapter 4 suggest that D. hirsutum

can produce a soil buffer in excess of 70 mm after 3 years. Given a longer pasture phase

it seems likely that an even larger buffer could be created.

Another opportunity for D. hirsutum could be integration in a polyculture with crops

(intercropping), as is currently being investigated for M. sativa (Egan and Ransom

2003; Humphries et al. 2003). The low winter activity and prostrate habit of D.

hirsutum make it suitable for this situation. In such a system, low densities of D.

hirsutum could be used to increase water use while providing some forage during

summer. However, the tolerance of D. hirsutum to strong competition is questionable,

and establishment would need to occur in less competitive situations (e.g. a year prior to

sowing crops) (Chapter 5).

The results of this project and a number of previous studies show that forage quality is a

major limitation to the use of Dorycnium species (Douglas et al. 1996a; Oppong et al.

2001; Davies and Lane 2003). For example, in Chapter 8 the digestibility of D. hirsutum

forage was well below the minimum required for animal maintenance (55% dry matter

digestibility) (Freer et al. 1997). Thus the greatest opportunity for Dorycnium is to

provide forage during the autumn feed gap, when annual pastures are dead and already

mostly utilised by livestock over summer and other forage sources (e.g. crop stubbles)

are of low quality and quantity. The provision of forage during this period has a high

economic value because it reduces the cost of supplementary feeding and can increase

the number of livestock that can be maintained (Bathgate and Pannell 2002). The

capacity of D. hirsutum to accumulate growth and maintain leaf area suggests that it

might be suitable to conserve as a forage source for this period.

Low forage digestibility in Dorycnium appears related to high concentrations of

condensed tannins (CT) (> 10%) (Terrill et al. 1992; Waghorn et al. 1998; Waghorn

and Molan 2001). Condensed tannins bind to protein and reduce digestion in the rumen

and can also reduce forage palatability (Barry and McNabb 1999). However, in spite of

the negative impacts of high CT concentrations on forage feeding value, they have a

number of possible benefits for animal health, such as prevention of bloat and reduction

in gastro-intestinal parasite numbers (Waghorn et al. 1998). In addition, dietary levels

of 2–4% CT can have positive effects on animal performance (Min et al. 2003).


194

Dorycnium forage stored as a forage reserve might be used strategically to achieve

animal health benefits. Alternatively, Dorycnium could be grown in mixtures with other

pasture species that might enable optimal dietary levels of CT to be consumed by

livestock.

However, CT are also known to reduce forage palatability (Waghorn et al. 2002) and

livestock may avoid forage with high concentrations. Intensive rotational grazing (e.g.

cell grazing) or short periods of heavy stocking might reduce or remove the impacts of

forage palatability on diet selection (Norton 1998). Little data exists on the impact of

CT on diet selection in mixed pasture swards but preferential grazing of accompanying

species may also have some advantages. First, it may reduce the grazing pressure on

Dorycnium until the availability or nutrition of the accompanying pasture is reduced,

thus improving persistence and enabling biomass to be accumulated in the absence of

defoliation. Secondly, if Dorycnium palatability is lower than weed species it could also

have weed control benefits, similar to those achieved by strategic use of the annual

legume biserulla (Biserulla pelicinus) (Revell and Thomas 2004).

The use of Dorycnium species as a drought forage source raises a number of questions

regarding grazing management. In particular, ungrazed Dorycnium will accumulate

woody material, which can constitute up to 70% of shoot biomass (Chapter 8). In this

regard, the ability of D. rectum to reshoot from the base after shoot material is removed

is advantageous as it would allow mechanical removal of woody material should it be

required. The management requirements of D. hirsutum are less obvious. Although

Dorycnium species are tolerant of hard grazing (Sheppard and Douglas 1986), frequent

intense defoliation can result in plant death (Chapter 8). Regrowth periods of > 8 weeks

are needed, which may be a problem if they are repeatedly defoliated in continuously

grazed pastures. No currently used forage species possess a similar plant form to

Dorycnium and thus grazing management guidelines that optimise production and

nutritive value of these species are not available. Further investigations are required.

Future research and development requirements

Despite the emphasis on D. hirsutum and D. rectum in this thesis, subspecies of D.

pentaphyllum may also be suitable for southern Australia. In New Zealand, D.

pentaphyllum is reported to be tolerant of similar drought-prone environments to D.

195

hirsutum (Wills 1983; Douglas and Foote 1994). D. pentaphyllum also has better forage

quality and higher palatability than D. hirsutum (Terrill et al. 1992; Wills et al. 1999).

However, in previous evaluations in Western Australia, D. pentaphyllum performance

has been poor (G. Moore, unpublished data). Current genetic resource holdings of D.

pentaphyllum rarely identify germplasm to the subspecies level, yet these variants may

originate from distinct ranges and may occur in quite different ecological circumstances

(Chapter 3). Thus, further evaluation of D. pentaphyllum is warranted in Australia but

must consider differences between variants within this species complex.

The evaluations of Dorycnium in this thesis involved genetic resources of unknown

origin and of questionable adaptation to Australian conditions. Material of potentially

greater suitability may be available. There is a capacity to expand the genetic resources

available and collect material with traits that would confer a high probability of success

in Australian climatic and edaphic conditions. For example, targeted collections from

regions with similar climate conditions (e.g. south-eastern Spain) (Chapter 3), and

especially from sites with coarse-textured acidic soils, should provide the most suitable

germplasm for the wheatbelt of Western Australia. In addition, a more comprehensive

survey of the site conditions where Dorycnium species are found would improve our

understanding of the ecological niches they occupy in their native distribution. Current

data is severely lacking in this area (Chapter 3).

Further agronomic evaluation and assessment of the genetic variation in Dorycnium in

relation to desirable agronomic traits is also needed. In particular, the potential for

improvements in seedling vigour and forage quality from breeding and/or selection

needs to be evaluated. Further evaluation of the acid-soil tolerance of Dorycnium

species and their associated root nodule bacteria is needed. Variation in the host-plant

and Rhizobium tolerance of stresses associated with soil acidity could enable material of

greater acid soil tolerance to be produced. The potential of Dorycnium species to use

additional water has been demonstrated. However, water use under different climatic

and edaphic conditions and the influence of plant density and timing and level of

defoliation require consideration. The nitrogen dynamics of Dorycnium-based pastures

have not been investigated. This is important to establish the nitrogen benefits for

subsequent crops or accompanying grasses and to investigate the possibility of

reductions in nitrogen leaching and soil acidification. Should breeding and


196

commercialisation of Dorycnium species progress, the reproductive system and seed

production requirements and capabilities will also need to be considered.

A large amount of research and development is still required in southern Australia to

better define where Dorycnium species perform best, to overcome their current

limitations and to provide a commercially viable option to farmers. This project has

greatly improved our understanding of the future potential and probable role of

Dorycnium species. I believe the agronomic traits investigated in this thesis provide a

good model for determining the potential role of other new forage species. Some of the

findings may also provide a useful guide on the farming systems which will be suitable

for other plants with similar morphology to Dorycnium.

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Prospects of Dorycnium species to increase water use in ... › files › ... · The potential of Dorycnium to increase water use was assessed in two field experiments in the wheatbelt