Subsoil ManuringCrop and Soil responses to an innovative practice 

in the low‐medium rainfall regions of VictoriaRenick Peries, Melissa Cann & Darryl Pearl (DEDJTR) &

Jaikirat S Gill & Peter Sale (LTU) 

What is subsoil manuring?

• A mechanical/engineering intervention

• Large volumes (10-20 t/ha) of Nitrogen rich manures placed within the clay matrix of soil in a single deep ripping operation.

The  problem with dense clay subsoils (HRZ)

Low macro‐porosity   ……roots cannot breatheHigh bulk density        ……roots struggle to penetrateLow infiltration            ……cannot capture rainfall in subsoilFrequently sodic ….. high sodium…ESP% > 15%

OUR APPROACH TO SOLUTIONS?(VICTORIAN HRZ VS LOW TO INTERMEDIATE RAINFALL REGIONS)

• Low water productivity despite high rainfall

• Dense clay subsoils with low macro-porosity

?

Increasing the capacity to store PAW:Catch more, store more grow more

Soil pit showing manure placed at depth

Photo: courtesy of SFS

subsoil manuring- benefits & setbacks

• Improves connectivity between topsoil & subsoil

•Improves aeration & conductivity

•Improves bucket size

•Improves soil biology ?

•Improves yield & WUE

•Currently Expensive

Subsoil manuring: how does it transform clay?manure

microbes

polysaccharides

+

clay particles

clay aggregates

Roots

clay particles

clay aggregates

SSM plot    30‐40 cmControl plot   30‐40 cm

……… 4 years after treatment

The amended clay layer is transformed

Increased macro‐porosity   ……roots can now breathe, less waterloggingLower bulk density               ……roots readily penetrate into subsoilRapid infiltration                   ……readily capture rainfall in subsoil

Crop and soil responses in the low-intermediate rainfall zone

Rainfall @ the Mallee trial sites2014 Site Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec RF(T) RF(GS)

Ouyen 3 64 6 63 21 10 17 4 62 3 25 15 292 179(84)

Hopetoun 8 9 14 64 22 21 23 8 14 2 26 7 211 154(92)

Charlton 5 8 36 56 23 35 24 7 13 11 41 16 275 169(57)

2015 Site Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec RF(T) RF(GS)

Ouyen 30 6 0.4 38 22 31 18 14 12 10 33 3.6 219 146(69)

Hopetoun 40 15 0.4 21 26 32 19 15 27 26 38 64 324 165(98)

Charlton 37 14 8 19 25 31 28 26 17 6 24 8.2 243 152(51)

Site Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec L‐T/(GS) mean

Ouyen 20.9 24.3 20.0 21.7 31.5 29.2 30.6 32.2 32.6 34.4 27.8 25.6 331.1 (212)

Hopetoun 33.9 14.2 17.6 21.5 25.0 24.1 26.3 24.8 23.2 22.7 29.9 29.3 293.3 (168)

Charlton 24.3 27.2 28.3 32.2 42.7 48.1 43.2 45.2 42.6 41.8 28.4 26.8 430.8 (296)

YEAR Rainfall period Rainfall(mm)

Decileranking

Comments

Summer (Dec.‐Feb.) 91 7.3Autumn (Mar.‐May) 90 7.5

2014 Winter (June‐August) 30.7 0.4 The 4th driest winter on record from 1913

Spring (Sept.‐Nov.) 90 5.6

Growing Season (Apr‐Oct.).) 179 3.9

Total Annual (Jan.‐Dec.) 293 3.9

Summer (Dec.‐Feb.) 51 3.9

Autumn (Mar.‐May) 61 4.8

2015 Winter (June‐August) 63 2.3

Spring (Sept.‐Nov.) 56 2.5

Growing Season (Apr‐Oct.) 146 1.8Total Annual (Jan.‐Dec.) 218 1.3

Mean annual rainfall  (1880‐2015)        330

Amounts and decile rankings for seasonal rainfall at Ouyen in 2014 and 2015,from Ouyen Post Office recording station

YEAR Rainfall period Rainfall(mm)

Decileranking

Comments

Summer (Dec.‐Feb.) 17 0.6 The second driest on record since 1998.

Autumn (Mar.‐May) 100 8.0

2014 Winter (June‐August) 52 1.7 .

Spring (Sept.‐Nov.) 42 0.6 The second driest on record since 1998.

Growing Season (Apr‐Oct.).) 154 2.3

Total Annual (Jan.‐Dec.) 211 1.3 The 3rd driest since on record since 1998.

Summer (Dec.‐Feb.) 62 6.4

Autumn (Mar.‐May) 150 10 The wettest on record since 1998.

2015 Winter (June‐August) 76 2.4 .

Spring (Sept.‐Nov.) 49 2.6

Growing Season (Apr‐Oct.) 155 2.7

Total Annual (Jan.‐Dec.) 246 3.3

Mean annual rainfall  (1904‐2015)        502

Amounts and decile rankings for seasonal rainfall at Hopetoun in 2014 and 2015measured at the nearby weather station at Wirrbibial Downs.

YEAR Rainfall period Rainfall(mm)

Decileranking

Comments

Summer (Dec.‐Feb.) 22 1.2

Autumn (Mar.‐May) 113 6.3

2014 Winter (June‐August) 66 0.8 The 5th driest on record since 1952.

Spring (Sept.‐Nov.) 74 2.7 .

Growing Season (Apr‐Oct.).) 223  1.7

Total Annual (Jan.‐Dec.) 279 1.3 .

Summer (Dec.‐Feb.) 64 4.8

Autumn (Mar.‐May) 52 2.1

2015 Winter (June‐August) 85 1.6 The 4th driest on record since 1956.

Spring (Sept.‐Nov.) 47 0.8 The 4th driest on record since 1952.

Growing Season (Apr‐Oct.) 176 0.9 The 5th driest on record since 1952.

Total Annual (Jan.‐Dec.) 243 0.9 The 5th driest on record since 1954.

Mean annual rainfall  (1954‐2015)        425

Amounts and decile rankings for seasonal rainfall at Charlton in 2014 and 2015measured at the nearby weather station in Donald St., Charlton 

Effect of subsoil manuring on the macro-porosity, saturated hydraulic conductivity, and bulk density in the 10-30 and 30-50 cm deep subsurface layers

Site Treatment

Macro‐porosity(%)

Sat. Hydraulic Conductivity (cm/hr)

Bulk Density(g/cm3)

Depth (cm) Depth (cm) Depth (cm)

10‐30 30‐50 10‐30 30‐50 10‐30 30‐50

OuyenControl 18.9 13.1 1.67 0.84 1.39 1.46Manured 17.5 15.6 1.67 1.05 1.38 1.41Significance NS NS NS * NS *P‐value 0.14 0.18 0.49 0.02 0.10 0.02

HopetounControl 10.1 ‐ 0.33 ‐ 1.39 ‐Manured 13.1 ‐ 0.65 0.15 1.33 1.38Significance * ‐ *** ‐ * ‐

Charlton

P‐value

ControlManured

SignificanceP‐value

0.013

9.412.5*

0.03

‐

‐‐‐‐

0.001

0.470.76NS0.10

‐

‐0.11‐‐

0.02

1.391.35*

0.04

‐

‐1.41‐‐

Grain/fodder yield obtained from the different Mallee sites where SSM was attempted in 2014

Site 2014 2015Treatment Crop Gr. Yield

(t/ha)Crop Yield (Gr/Fodder)

(t/ha)Ouyen SSM Barley 1.6 Wheat 0.86

Control Barley 0.3 Wheat 0.68Hopetoun SSM Wheat 1.3 Vetch 0.32

Control Wheat 1.72 Vetch 0.34Charlton SSM Wheat 0.41 Barley 1.17

Control Wheat 0.9 Barley 1.17

NO – SSM will NOT work in dry country

YES – SSM will work in dry country

• Not enough rain to open up / fill “subsoil bucket” 

• Chemical constraints limit SSM

• Remote manure sources.

• SSM more cost‐effective, farmer‐friendly; not reliant on manures

• Very effective water capture, top‐soil and subsoil

• Chemical constraints not limit SSM

Conclusions:• These trials were conducted in ‘tough’ environments in ‘tough’ times. Below average rainfall at

most sites impacted on crop growth and root proliferation.

• Inadequate rainfall to fill the bucket and to drive crop growth and root proliferation that will trigger soil change, appeared to result in limited success with SSM in the low tomedium rainfall zones.

• Despite the above, changes were still observed at some sites in the physical parameters monitored.

• Timing of rainfall appeared to be important to trigger soil-root-microbial interactions: something that could not be expected in sub-optimal rainfall years.

• Marginal differences in seasonal crop water use was observed that also resulted in small differences in grain yield.

• Some sites showing exceptional results are worthy of being followed up for a few more years to better understand the process of subsoil change in the low to medium rainfall zone.

• Chemical constraints may have contributed to inconsistent soil physical change contrary to the expectation from SSM.

CURRENT STATUS OF THE PRACTICE OF SSM

• One paddock scale SSM machine in Victoria (1000+ ha) • 4-5 Small scale SSM plot machines in Victoria, Southern NSW

SA, WA and Tasmania

• .

Thank You