Copyright is owned by the Author of the thesis. Permission is given for a copy to be downloaded by an individual for the purpose of research and private study only. The thesis may not be reproduced elsewhere without the permission of the Author.

AN ASSESSMENT OF THE NITROGEN FERTILIZER REQUIREMENTS OF WINTER CABBAGES

(Brassica oleracea var. capitata L.)

A thesis presented in partial fulfilment of

the requirements for the degree of

Doctor of Philosophy in Soil Science

at Massey University

ROBERTO REGINALDO BONOAN

1990

ii

ABSTRACT

The increasing costs of i\ fertilizers and the danger of creating

environmental pollution due to excessive N fertilisation practices create a

need for more efficient N fertilisation of vegetable crops. This present

study was conducted with the main objective of assessing the N fertilizer

requirements of winter cabbages on a coarse loamy mixed mesic Oystric

Eutrochrept soil and consequently developing a model which would assist in

predicting N fertilizer requirements over a wider area.

Glasshouse and field experiments were conducted to assess the utility of

soil and plant (sap) tests for assisting in determining the N fertilizer

requirements of winter cabbages. The concentrations of N03-N and NH4-N

in either the xylem or petiole sap of cabbages were found to be influenced

by several factors such as leaf position, time of day, sample storage time,

plant age and form of fertilizer N.

A large field trial indicated that at 4 sampling dates (50, 60, 80 and 90

days after transplanting; OAT) and prior to sidedressing, xylem (R 2 =

0.73 ....... ) and petiole (R 2 = 0.86""-) sap were strongly correlated to

extractable N03-N and NH4-N in the soil to a depth of 30 em. Nitrate-N

levels in xylem sap at 60 and 80 OAT and petiole sap at 50, 60 and 80

OAT were good predictors of harvestable fresh head yield. Maximum

marketable fresh . head yield (55 t/ha) was achieved with an initial N

application of 300 kg N/ha over a growing period of 150 days in which 448

mm of drainage was estimated. At heading, on the 300 kg N ha- 1, soil

mineral N levels were 75 kg 1\ ha-t, xylem sap concentration was 333 J.lg

N03-N ml- 1 and 1651 f.lg N03-N ml- 1 in the petiole sap. This cri~ical

value for petiole sap is higher than that reported in the literature for

cabbages. At petiole sap levels below the critical value, sidedressing with

100 kg N/ha as urea was required to achieve a similar yield as found with

an initial application of 300 kg N ha- 1 as calcium ammonium nitrate.

In a small scale field experiment, plant recovery (62-65%) of sidedressed

iii

1 5 N labelled urea N did not differ between sidedressing rates (100 and 200

kg N). Total recovery of 1 5 N in the plant and soil was considered high

(114 + 0.9% and 90 + 1.1%) for the respective rates.

Using the data obtained from the field trials, a simple model termed a

"sidedressing model" was developed. The model specifically determines the

amount of N fertilizer needed to be applied as a sidedressing at a critical

time (heading) to obtain maximum yield. The model was validated, using

the data from another N fertilizer field trial conducted in the following

year. The model successfully predicted whether N sidedressing is required

or not but only a limited validation could be made of the prediction rates.

The limitation of the sidedressing model of being site and season specific

can be reduced by using simple submodels to predict the measured

component which assessed N in cabbages at heading (Nh). One submodel

used (the heat unit model) was modified by including data from 2-year

trial results, to predict Nh and also provided a prediction of N uptake at

maturity (Ny). Although not able to be validated in this study, the model

shows potential for use by environmental administrators in predicting the

likely effects of various growers practices in relation to identifying

problems associated with N03-N in drinking water and in edible cabbage

heads.

iv

ACKNOWLEDGEMENTS

I am extremely grateful to:

Dr Paul Gregg and Dr Mike Hedley for their supervision, guidance,

patience and friendship during my studies.

Other members of the Soil Science Department for valuable discussions and

assistance during the work.

Dr Santiago Obien, director of the Philippine Rice Research Institute, for

the encouragement to pursue postgraduate studies.

Ms Lee Heng and Mr Wichien Chatupote for assistance with computer work

and final preparation of this thesis. Mr Donald Tambunan and other

postgraduate students and all technicians in the Department for help with

glasshouse and field work.

All Filipino friends particularly Mr and Ms Angel Carambas.

The Ministry of External Relations and Trade of New Zealand for the

scholarship grant.

The National Tobacco Authority of the Philippines for the study leave.

Lastly, but most important, to my mother, brothers and sisters for their

great moral support.

v

TABLE OF CONTENTS

ABS'fRACT ............................................................................ ..................... ii

ACKNOWLEDGEMENTS .............................................................................. iv

TABLE OF CONTENTS ............................................................................... v

LIST OF FIGURES ..................................................................................... xi

LIST OF TABLES ...................................................................................... XV

CHAPTER 1

INTRODUCTION .......................................................................................... 1

CHAPTER 2

REVIEW OF LITERATURE

2.1 NITROGEN FERTILIZER REQUIREMENTS OF CROPS, PARTICULARLY VEGETABLE CROPS ........................ 3

2.2 DIAGNOSTIC TESTS FOR DETERMINING N FERTILIZER REQUIREMENTS OF CROPS ..................................... 4 2.2.1 Soil Testing ....................... ~ .............................................. 4 2.2.2 Plant Analysis .................................................................. 6

2.2.2.1 Total 1V ••••••••••••••••••••••••••••••••.••••.••.•.••••••••••••••• 6 2.2.2.2 Extractable N ................................................ 8 2.2.2.3 Sap nitrate testing ......................................... 9

2.2.3 Factors Affecting Nitrate Concentrations in Plants ........ 14 2.2.3.1 Genetic control ............................................ 14 2.2.3.2 Light and temperature ................................. 15 2.2.3.3 Rate and amount of nitrate supply .............. 16 2.2.3.4 Form of fertilizer N .................................... 17 2.2.3.5 Time and method of N application ............... 18 2.2.3.6 Other macronutrients ................................... 19 2.2.3. 7 Nitrification inhibitors .................................. 19

2.2.4 Critical N Levels in Vegetables ...................................... 20

2.3 EFFECT OF FERTILIZER FORM ON GROWTH AND YIELD OF CROPS •.......•.......•...........................................•. 23 2.3.1 Effect of N Fertilizer Form ........................................... 23 2.3.2 Effect of Fertilizer (N/P) Forms .................................... 25

2.4 FATE OF FERTILIZER N IN SOILS •.••.•......•......••.•.•....•.••......•..... 27 2.4.1 Value of 15N Labelled Fertilizer .............................•...... 27 2.4. 2 Fertilizer N Balance Studies •.......................................... 28

vi

2.5 MODELLING THE N FERTILIZER REQUIREMENTS OF CROPS ................................................... .. ............................. 32

CHAPTER 3

METHODS OF MEASURING SAP NITRATE CONCENTRATIONS IN CABBAGES

3.1 INTRODUCTION .......................................... . ............................... 41

3. 2 OBJECTIVE .............................................. . ................................... 42

3.3 MATERIALS AND METHODS ....................................................... 42 3.3.1 Soil ................................................................................ 42 3.3.2 Plant Growth .................................................................. 42 3.3 .3 Fertilizer Treatments ..................................................... 44 3.3.4 Plant Harvest ................................................................. 45 3.3.5 Plant Analysis ...................................... ... . ...................... 45

3.3.5.1 Petiole sap N03-N .......... ... .......................... 45 3.3.5.2 Xylem sap N03-N ........ .......... . .... ................. 46 3.3.5.3 Acetic acid soluble N03-N. . ... ....... ............... 46 3.3.5.4 Total N in whole plants .. ............................. 48

3.3.6 Soil Analysis ................................................................ ... 48 3.3. 7 Statistical Analysis ........................................ .. ... ........... . 48

3.4 RESULTS AND DISCUSSION ........................................................ 48 3.4.1 Effect of N on Yield ..................................................... 48 3.4.2 Effect of N on Total N Uptake ....................... . ............. 50 3.4.3 Relationship Between Total Plant N and Plant Sap

N03-N Concentrations and Rate of N Application .......... 52 3.4.3.1 Effect of N on petiole sap N03-N ............... 52 3.4.3.2 Effect of N on xylem sap N03-N ................ 57 3.4.3.3 Effect of N on acetic acid soluble

N03-N ...............................................•......... 60 3.4.3.4 Effect of N on total N ................................ 60

3.4.4 Effect of N on Soil N03-N and NH4-N .......................... 62 3.4.5 Relationships Between the Merck Test Strip and

the Standard Laboratory Methods of Measuring N03-N .•. 67 3.4.6 Comparison of the Methods for Xylem Sap Collection ..•. 69 3.4.7 Relationship Between Plant N Concentrations and

Final Yield ..............................•..................•................... 69

3.5 CONCLUSION .................................................................... : ......... 73

CHAPTER 4

FACTORS AFFECTING SAP NUTRIENT CONCENTRATIONS IN CABBAGES

vii

4.1 INTRODUCTION .......................................................................... 7 5

4.2 OBJECTIVE .................................................................................. 75

4.3 MATERIALS AND MEl'HODS ....... ................................................ 75

4.4 RESULTS AND DISCUSSION ........................................................ 76 4.4.1 Effect of Leaf Position .................................................. 76 4.4.2 Effect of Time of Day ................... . ............................... 79 4.4.3 Effect of Sample Storage Time ...................................... 81 4.4.4 Effect of Plant Age ....................................................... 84 4.4.5 Plant to Plant Variability of Petiole Sap N03-N ............ 86

4.5 CONCLUSION ................ ....... ...................................... ................. 87

CHAPTER 5

INFLUENCE OF FERTILIZER FORMS ON SAP NUTRIENT CONCENTRATIONS AND YIELD OF WINTER CABBAGES

5.1 INTRODUCTION .......................................................................... 88

5.2 OBJECTIVES ..........•.•...•............................................................... 89

5.3 MATERIALS AND MEl'HODS .•••....•....•...............••......•...............•. 89 5.3.1 Laboratory Experiment ........................................ ........... 89

5.3.1.1 Preparation of PAPR ................................... 89 5.3.1.2 Preparation of NIP APR ................................ 90 5.3.1.3 Moisture content of the fertilizers ............... 91 5.3.1.4 Total N and P contents of the

fertilizers ..........•.......................................... 94 5.3.1.5 Solubility of the fertilizers .......................... 94

5.3.2 Glasshouse Experiment {1987) ....••...•.•.•.........•........•...•...• 95 5.3.3 Field Experiment (1988) .••...•.• ~ .•.•..•...•.•...•....•.•........•.•...• 1 00

5.4 RESUL'fS AND DISCUSSION .................. ~ •••...•.••••.••.••.•••••.•.•.•••••.• 101 5.4.1 Glasshouse Experiment ................................................... l01

5.4.1.1 Effect of N fertilizer form on N03- and NH.,.-N concentration in xylem sap .............. lOl

5.4.1.2 Effect of P fertilizer from on N03- and NH.,.-N concentration in xylem sap .............. 104

5.4.1.3 Effect of N fertilizer form on PO.,.-P concentration in xylem sap .............. 107

5.4.1.4 Effect of fertilizer form (NIP) on PO.,. -P concentration in xylem sap ......... ..... 1 07

5.4.1.5 Effect of straight N and straight P fertilizer form on dry matter yield ••••.•...•... 109

viii

5.4.1.6 Effect of fertilizer form (NIP) on dry matter yield ................................................ 109

5.4.1. 7 Effect of N fertilizer form on soil pH ...... . 115 5.4.1.8 Extractable NH4- levels in the soil. .......... . 115 5.4.1.9 Soluble salt concentration in soil

extracts ..................................................... . 120 5.4.2 Field Experiment ........................................................... l20

5.4.2.1 Yield, NIP concentrations and NIP uptake ......................................................... l23

5.5 CONCLUSIONS ........................................................................... 125

CHAPTER 6

PREDICTING NITROGEN FERTILIZER REQUIREMENTS OF WINTER CABBAGES BY PLANT (SAP) AND SOIL TESTS

6.1 INTRODUCTION ......................................................................... 127

6. 2 OBJECTIVE ................................................................................. 128

6.3 MATERIALS AND METHODS ...................................................... 128 6.3.1 Sap Sampling Techniques ............................................... 131 6.3.2 Soil Measurements ......................................................... l31 6.3.3 N Depletion Zone Around the Roots of a Cabbage

Plant .....................................•..................................... 132 6.3.4 Meteorological Data ...................................................... 132

6.4 RESULTS AND DISCUSSION ....................................................... 132 6.4.1 Meteorological Conditions .............................................. 132 6.4.2 Effect of N Sidedressing on Xylem Sap N03-N ............. 134 6.4.3 Effect of Sidedressing on Petiole Sap N03-N ................ 134 6.4.4 Soil N03- and NH4-N Concentrations ............................ 137 6.4.5 N Depletion Zone Around the Roots of a Cabbage

Plant ............................................................................. 140 6.4.6 Correlation of Soil and Sap Tests .................................. 145 6.4. 7 Relationships Between Sap N Concentration and

Harvestable Fresh Head Yield ....................................... 148 6.4.8 Critical Plant Sap N03-N Concentrations ...................... 153 6.4.9 Effect of N Rates on Cabbage Head Yield and N

Uptake .......................................................................... 159 6.4.10 Effect of Sidedressing on Marketable Fresh Head

Yield ............................................................................. 159

6.5 CONCLUSION ................................................................................... 159

CHAPTER 7

EFFICIENCY OF 1 :sN LABELLED UREA FERTILIZER APPLIED AS A SIDEDRESSING TO WINTER CABBAGES

ix

7.1 INTRODUCTION ......................................................................... 162

7.2 OBJECTIVE ............•.......•..............•.......................................•..... 162

7.3 MATERIAI..S AND MEfHODS ...................................................... 162 7. 3.1 Sampling and Analytical Procedures ............................... 163

7.3.1.1 Plant ....... .................................................... 163 7.3.1.2 Soil .... ................................. ........................ 165 7.3.1.3 Soil solutions ............................................... 165 7.3.1.4 1 :sN analysis ................................................ 165

7.4 RESULTS AND DISCUSSION ....•.................................................. 166 7 .4.1 Yield, N concentrations and N Uptake .......................... 166 7.4.2 Recovery of Labelled Fertilizer N in the Plant ............. 167 7 .4. 3 Recovery of Labelled Fertilizer N in the Soil ............... 17 4 7 .4.4 Balance of Applied Labelled Fertilizer N ...................... 176 7 .4. 5 Extrapolation of Results From 1 :sN Plot to the Main

Trial. ............................... .................................. ... ......... 180

7.5 CONCLUSION ............................................................ . .•........... ... 180

CHAPTER 8

MODELLING THE NITROGEN FERTILIZER REQUIREMENTS OF WINTER CABBAGES

8.1 INl"RODUCTION ......................................................................... 185

8.2 GENERAL METHODOLOGY .................•..............•.•...••..•.••..•..•.... 185

8. 3 RESULTS AND DISCUSSION .••....•................•••••.••.....•.••..........•... 186 8.3.1 The Sidedressing Model. .......... ~ ..•.•..•......•............•.......... 186 8.3.2 Development of the Model ...........•..•.......••.•.•................ 187

8.3.2.1 Nitrogen demand (Ny, Nh) .••••••••.•••.•....••••.•.. 187 8.3.2.2 Nitrogen supply (N., NmJ ............................ l88 8.3.2.3 Efficiency of plant uptake {E., Er) ......... .... 189

8.3.3 Validation of the Sidedressing Model .....................•....... l89 8.3.4 DiscusSion of Validation ............•..•...•....•........................ l92 8.3.5 Possibilities for Improving the Model.. ...•....•.•••......•....... l98

8.3. 5.1 Predicting Nh················ .............................. l98 8.3.5.2 Predicting N • .............................................. 217

8.4 CONCLUSION ••.••.••.•.•.•.•••••••.•••••.•.••..•.•.••••••.•••.•••••••••.••••••••.•••.•.•. 224

X

CHAPTER 9

SUMMARY ............................................................................................... 226

BIBLIOGRAPHY ............................... ........................................................ 231

APPENDICES ........ ................ .... ........... ......................... ... ........................ 247

Figure 3.1

Figure 3.2

Figure 3.3

Figure 3.4

Figure 3.5

Figure 3.6

Figure 3.7

Figure 3.8

Figi.Ire 3.9

Figure 3.10

Figure 3.11

Figure 4.1

Figure 4.2a

Figure 4.2b ·

Figure 4.3

xi

LISf OF FIGURES

Method of xylem sap collection using filter paper strips .............................................................................. 47

The effect of N application rate on fresh head yield of cabbages at final harvest ........................................... 49

The effect of N application rate on total N uptake by cabbages at final harvest .......................................... 52

The effect of N application rate on petiole sap N03-N concentration measured by the Merck test strip ......................................................................... . ..... 55

The effect of N application rate on petiole sap N03-N concentration measured by the autoanalyser method ........................................................................... 56

The effect of N application rate on xylem sap N03-N concentration measured by the autoanalyser method ....... 59

The effect of N application rate on acetic acid soluble N03-N in cabbage tissues ................................... 61

The effect of N application rate on total N contents (roots + shoots} in cabbages ........................................... 63

The effect of N application rate on N03-N concentration in the soil ................................................ 64

The relationship between soil and sap tests .................... 65

Comparison of (a} N03-N and (b) NH4-N concentrations in xylem sap of cabbages collected by different methods ........................................................... 70

Showing the position of (a) young mature leaf (YML) and (b) wrapper leaf (WL) within a cabbage plant .......... 77

The effect of leaf sampling position on the petiole sap N03-N concentration of cabbage at heading (glasshouse experiment) ................................................... 78

The effect of leaf sampling position on the petiole sap N03-N concentration of cabbage at heading (field experiment) ........................................................... 80

The effect of time of day on xylem and petiole sap N03-N concentrations in cabbages .................................. 82

Figure 4.4

Figure 4.5

Figure 5.1a

Figure 5.1b

Figure 5.2a

Figure 5.2b

Figure 5.3

Figure 5.4

Figure 5.5

Figure 5.6

Figure 5.7

Figure 5.8

Figure 5.9

Figure 6.1

Figure 6.2

xii

The effect of sample storage time on xylem sap N and P concentrations in cabbages ................................... 83

The effect of plant age and rates of N application on (a) xylem and (b) petiole sap N03-N concentrations in cabbages ..................................... . ....... 85

The effect of N fertilizer form on N03-N concentration in xylem sap of cabbages. Rate of N application (N g/pot): NO(O); Nl(l); N2(2) and N4(4) ...................................................................... 102

The effect of N fertilizer form on NH4-N concentration in xylem sap of cabbages. Rate of N application (N g/pot):NO(O); Nl(1); N2(2); N4(4) .............. 103

The effect of P fertilizer form on N03-N concentration in xylem sap of cabbages. Rate of N/P application (N/P g/pot): NO(O); N2(2); N4(4) .... ........ 105

The effect of P fertilizer form on NH4-N concentration in xylem sap of cabbages Rate of N/P application (N/P g/pot): NO(O); N2(2); N4(4) ............ 106

The effect of N fertilizer form on P concentration in xylem sap of cabbages Rate of N application (N g/pot): NO(O); Nl(l); N2(2) and N4(4) ............................. 108

The effect of N/P fertilizer form as Urea/PAPR on P concentration in xylem sap of cabbages ..................... ll 0

The effect of (a) straight N and (b) straight P fertilizer forms on dry matter yield of cabbages .......... 111

The effect of N/P fertilizer form as Urea/PAPR on dry matter yield of cabbages ........................................ 113

The effect of N/PAPR and N/MCP fertilizer forms on dry matter yield of cabbages. Rates of P application are given in Table 5. 5 ................................. 114

The symptoms of NH4... toxicity exhibited by cabbage plants fertilised with AmS/PAPR at 4 and 5 N/P g/pot . application rate ...•........................................ 119

The relationship between specific conductivity and percent yield reduction of cabbages at 40 DA T .........•.. 122

General view of the field experiment ...•........................ 129

Total monthly rainfall during the conduct of the

Figure 6,3

Figure 6.4

Figure 6.5

Figure 6.6a

Figure 6.6b

Figure 6.7a

Figure 6.7b

Figure 6.8

Figure 6.9a

Figure 6.9b

Figure 6.10

Figure 6.11

Figure 6.12

Figure 6.13

Figure 6.14

Figure 7.1

Figure 7.2

xiii

experiment relative to the 10-year average ................... 133

N03-N concentration in xylem sap of cabbages (f) Indicates time of N fertilizer sidedressing ..................... 135

N03-N concentration in petiole sap of cabbages. (f) Indicates time of N fertilizer sidedressing ..................... 136

Petiole sap N03-N concentration in relation to soil N after N fertilizer sidedressing ................................... 138

Soil N03- + NH .. -N concentrations (0-30 em depth) at each harvest ...........................................•................. 139

Soil N03-N concentrations ( > 30 em depth) in relation to cumulative drainage .................................................. 141

N03-N depletion zone around cabbage roots at (a) 20 ·and (b) 40 DAS ........................................................ 142

NH4-N depletion zone around cabbage roots at (a) 20 and (b) 40 DAS ........................................................ 143

Correlation between soil and sap tests .......................... 144

Harvestable fresh head yield vs xylem sap N03-N measured at various sampling dates ............................... 146

Harvestable fresh head yield vs petiole sap N03-N measured at various sampling dates ............................... 147

The relationship between S and nitrate concentration in (a) xylem and (b) petiole sap .................................... 150

The effect of N additions on dry matter yield of cabbages ........................................................................ 154

The effect of N additions on harvestable fresh head yield ............................................................................... 15.5

The effect of N additions on N uptake by cabbages ........................................................................ 157

Percent recovery of fertilizer N ................................... 158

Showing the microplots used in the 1 5 N field experiment ..................................................................... 164

The effect of rate of N fertilizer sidedressing on total (roots + shoots) dry matter yield of cabbages ........................................................................ 168

Figure 7.3

Figure 7.4

Figure 7.5

Figure 7.6

Figure 7.7

Figure 8.1

Figure 8.2

Figure 8.3

Figure 8.4

Figure 8.5

Figure 8.6

Figure 8.7

.. xiv

Total N concentrations in cabbages ............................... 170

Total N uptake (roots + shoots) by cabbages ................. 171

Balance of applied labelled fertilizer N in the plant and soil ................................................................ 178

Daily rain and drainage data after sidedressing 1 ~N fertilizer ....................................................................... 181

N03-N concentrations in water samples collected at 30 em depth .................................................................. 182

The effect of N additions on harvestable fresh head yield of cabbages in the 1989 field trial.. ..................... 193

The %N in the dry matter yield (above ground parts of cabbages plotted against their dry matter yield measured at intervals during growth on treatments (x) 300 and (+) 0 kg N/ha in the 1988 field tria1. ......... 203

Predicted N uptake (N kg/ha) by winter cabbages (above ground parts) against heat units in the (a) 1988 and (b) 1989 field trial ......................................... 209

The relationship between B/Bmax and petiole. sap N03-N concentrations at heading in the (a) 1988 and (b) 1988 + 1989 field trials ........................................... 211

The relationship between fresh head yield (t/ha) and N uptake (N kg/ha) by cabbages at final harvest for the 1988 and 1989 field trials (pooled data) .................. 218

Measured and predicted soil N levels (N kg/ha) prior to (+) and at heading (x) in the 1989 field trial.. .......... 220

Available N (N03- + NH"-N) in the soils (0-30 em depth) from transplanting to heading in (a) 1988 and (b) 1989 field trial ...............................................•........ 223

Table 2.1

Table 3.1

Table 3.2

Table 3.3

Table 3.4

Table 3.5

Table 3.6

Table 3.7

Table 3.8

Table 3.9

Table 5.1

Table 5.2

Table 5.3

Table 5.4

Table 5.5

XV

LIST OF TABLES

Nitrogen levels in cabbages as reported in the literature ........................................................................ 21

Properties of Manawatu fine sandy loam topsoil used in the glasshouse experiment. ......................................... 43

Total dry matter yield (g/pot) of cabbages at different sampling dates ................................................. 51

Total N uptake (N g/pot) by cabbages at different sampling dates ................................................................ 53

Correlation between N application rate and sap N03-N acetic acid soluble N03-N and total N using a quadratic function (n=32) ............................................. 54

The effect of N fertilizer rates on N concentrations in cabbages at 60 OAT .................................................. 58

Soil N03- + NH"'-N (pg/g soil) after each harvest .......... 66

Linear correlation coefficients (r) between Psap N03-N concentrations determined by the Merck test strip and the autoanalyser method and acetic acid extraction (n=32) ................ , ........................................... 68

Linear regression equations showing the relationship between Psap N03-N concentrations measured by Merck test strip and autoanalyser method (n=32) ............ 68

Summary of regression coefficients (R2 ) of the predictive equations relating plant N parameters at 60 OAT and final yield of cabbages (n=32) ..................... 72

Yield weights of the different fertilizer materials ......... 92

Total N(%N) and total P(%P) analyses of the N/PAPR fertilizers (oven-dry basis, 90°C for 24-hr) ....... 93

The total P content and the percentage P extracted from different N/PAPR products by water, 2% citric and 2% formic acid ..... . .......................... ........................ 96

Dry matter yield (g/pot) of broccoli from the preliminary glasshouse experiment .................................. 98

Forms and rates of NIP; N or P application in the glasshouse experiment ..................................................... 99

Table 5.6

Table 5.7

Table 5.8

Table 5.9

Table 5.10

Table 5.11

Table 6.1

Table 6.2

Table 6.3

Table 7.1a

Table 7.1b

Table 7.2

Table 7.3

Table 7.4

Table 7.5

Table 8.1

Table 8.2

Table 8.3

Table 8.4

xvi

Effect of fertilizer forms (N/P) on dry matter yield (g/pot) of cabbages ............... .... ................................. .... 116

Soil pH at each harvest .. ............. ....... ... ............. ... . ... ... 117

Extractable NH"'-N levels (J,Lg/g) in the soils and %N concentrations in plants after each harvest. ............... ... 118

Conductivity of saturated soil extracts (.umbos/ em) at 40 DAT ................................. ........ ... . ............... . . ... ... 121

The effect of fertilizer form on dry matter yield and fresh head yield (g/plant) of cabbages ............. . ... .. . 124

N and P concentrations (%) and N and P uptake (g/plant) by cabbages at final harvest . ....... .. ...... . ..... ..... 124

Some initial properties of Karapoti fine sandy loam topsoil used in the field experiment. .. ............ ............ ... 130

Cabbage data and simulation results using xylem sap .... 151

Cabbage data and simulation results using petiole sap .. . 152

The effect of rate of N fertilizer sidedressing on harvestable fresh head yield (kg/plant) of cabbages ....... 169

The effect of rate of N fertilizer sidedressing on total dry matter yield (g/plant) of cabbages ..... . ............ 169

Recovery of labelled fertilizer N in the plant .......... . .... 173

Recovery of labelled fertilizer N in the soil.. . ..... ... . .. ... l75

Balance of applied labelled fertilizer N in the plant and soil .... . ............... . ............... ..... .... ... .... . .... . .. ..... .... .... 177

Statistical analysis of fresh head yield and N uptake in the 1 :sN plot (A) and main trial (B) ....... ..... . ............. 183

Fertilizer N (N,.) sidedressing requirements of winter cabbages in the 1989 field trial ............ ... ....... . ............. 191

Monthly rainfall (mm) and drainage (mm) during the conduct of the field experiments . ........... . ...................... 195

Measured and predicted Nm (N kg/ha) from heading to final harvest in the 1989 field trial.. ........................ 195

N03-N concentrations (pg/ml) in petiole sap (YML) of winter cabbages at two sampling growth stages in