UNIVERSITI PUTRA MALAYSIA

SEASONAL DRY MATTER PRODUCTION AND NITROGEN FIXATION OF LEUCAENA (LEUCAENA LEUCOCEPHALA)

AND STYLO (STYLOSANTHES GUIANENSIS) IN PURE SWARDS AND IN ASSOCIATION WITH SIGNAL GRASS

(BRACHIARIA DECUMBENS)

AMINAH BT HJ. ABDULLAH

FP 1989 5

SEASONAL DRY MATTER PRODUCTION AND NITROGEN FIXATION OF LEUCAENA (LEUCAENA LEUCOCEPHALA) AND STYLO (STYLOSANTHES

GUIANENSIS) IN PURE SWARDS AND IN ASSOCIATION WITH SIGNAL GRASS (BRACHIARIA DECUMBENS)

By

AMINAH BT HJ . ABDULLAH

A Thesis Submitted in Partial Fulfilment of the Requirements for the Degree of Master of Agricultural

Science in the Faculty of Agriculture Universiti Pertanian Malaysia

January 1989

ACKNOWLEDGEMENTS

I wish to express my sincere gratitude and

appreciation to my supervisor , Assoc . Professor Dr . Wan

Mohamad Wan Othman and co-supervisor , Assoc . Professor

Dr . Haj i Zulkifli Haj i Shamsuddin for their guidance ,

invaluable suggestions and comments , advice and support in

the planning and implementation of the experiment and the

preparation of this thesis .

I am grateful to the Director-General of Malaysian

Agricultural Research and Development Institute ( MARDI)

for permitting me to pursue my study as a part- time

student at the Universiti Pertanian Malaysia.

Special thanks are due to the Director of Livestock

Division , Mr . Ahmad Tajuddin Zainuddin for his motivation

and encouragement throughout the programme .

Special thanks are also extended to Mr . Ahmad Shokri

Hj. Othman for his assistance in statistical analysis , Mr .

Nantha Kumaran and the staff of Animal Nutrition

Laboratory and Mr . Abbas Ghani and the staff of Central

Research Laboratory for chemical analyses of samples .

11

The assistance of Selamat Basar and Anuar Nordin in

supervising the experiment in the field is greatly

acknowledged .

Finally , my deep appreciation is extended to my

husband , Lakman Musa , who has spent much of his time

helping me and my children , Nur Ashikin , Nur Shakirin and

Nur Shafikah , who inspired me throughout the study .

iii

TABLE OF CONTENTS

Page

ACKNOWLEDGEMENTS. . . . . . . . . . • • • . . . . . . . . . . . . . . . . . . . . . ii

LIST OF TABLES . . . . . . . . . . . . . . . . . . . . . • . • • . . . . . . . . . . viii

LIST OF FIGURES................................... x

LIST OF PLATES . . . . . . . . . . . . . . . . . . . • • • . . . . . . . . . . . . . xi

ABSTRACT ......................................... xii

ABSTRAK .......................................... xv

CHAPTER 1 INTRODUCTION . . . . . . • . . . . . . . . . . . . . . . 1

CHAPTER 2 : REVIEW OF LITERATURE 4

Sources of Nitrogen (N) for Grassland Production . . • . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Nitrogen Requirements and its Absorption by Plants ............................. 4

Nitrogen Fertiliser and its Availabili ty . . . . . . . . . . . . . . . . . . . . . . • . . . . . . . . . . . . . . 5

Symbiotically-fixed N2

from Pasture Legumes . .................... . .......... . .... . . . . . 7 Nodulation and N

2 Fixation by

Pas ture Legumes . . ...... . ......... . ........ . . . .... 8

Effects of Defoliation on Nodulation and N

2 Fixation ....................... 11

Transfer of N2

from Legumes to the Associated Grass ................................. 13

Nitrogen Application during Initial Legume Establishment ............................. 14

Effects of N Fertiliser on Dry Matter Yield and Crude Protein Contents of Pastures.............................. 16

iv

Effects of Pasture Legumes on Dry Matter Yield and Crude Protein Contents of Pastures........... . . . . . • • . • . . . . . . . . . . 18

Plant Age and Crude Protein of Pastures. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 Digestibility of Tropical Forages................. 23

Nitrogen Fertiliser and its Effects on Soil Properties . . . . . . • . . . . . . . . . • . . . . . . . . . . . . . . 26

Roles of Legumes in Soil Improvement ...................................... 27 Animal Production from N-fertilised Pas tures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

Animal Production from Legume-based Pastures. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

CHAPTER 3 : MATERIALS AND METHODS

A Preliminary Trial - Soil Heterogeneity Test Using Maize

33

Plants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

Introduction 34

Plot Number, Size and Spacing • . . . . . . . . . . . . . . . . 34

Harves ting . . . . . . .. . . . . . . . . . ..... . . . .. . . . . . . . . . 35

The. Main Experiment .............................. 35

Basal Fertiliser Application...................... 35

Establishment of Forage Species . . . . • • . . . . . . . . . . . . 36

Weed Control ..................................... 37 Treatments and Experimental Design................ 37 Harvesting and Plant Sampling .................... 39

Soil Sampling . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . 40

Plan t Chemical Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . 40

N, P, K. Ca and Mg............................ .. 40

v

Soil Chemical Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 1

Soil pH . . . • . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 1

Lime Requirements o f Soil . . . . . . . . . . . . . . . . . . . . . . 41

Total N . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42

Available P . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42

Exchangeable K, Ca and Mg . . . . . . . . . . . . . . . . . . . . . . 42

In-vi tro Digestibility of Forages . . . . . . . . . . . . . . . . . . 43

Estimation of N2 Fixed by Legumes . . . . . . . . . . . . . . . . . . 44

Statistical Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44

CHAPTER 4 : RESULTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45

Rainfall . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45

Dry Matter Yield of Maize . . . . . . . . . . . . . . . . . . . . . . . . . 45

Stylo Survival Count . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48

Leucaena Plant Height 48

Leucaena Shoot Height 51

Leucaena Number of Branches . . . . . . . . . . . . . . . . . . . . . . . 51

Pasture Dry Matter

Leaf to Stem Ratio

yields . . . . . . . . . . . . . . . . . . . . . . . . . . 54

62

Botanical Composi tion of Pasture . . . . . . . . . . . . . . . . . 63

Crude Protein Content , Percentage N and in-vitro Dry Matter Digestibility ( IVDMD ) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68

Total N Yield and N Use Efficiency . . . . . . . . . . . . . . . . 70

Estimation of N2 Fixation . . . . . . . . . . . . . . . . . . . . . . . . . 74

Mineral Composition of Forage . . . . . . . . . . . . . . . . . . . . 75

Soil Chemical Properties . . . . . . . . . . . • . . . . . . . . . . . . . 77

vi

CHAPTER 5 : DISCUSSION . . . . . . . . . . . . . . . . . . . . . . . . 79

Pasture Dry Matter yields . . . . . . . . . . . . . . . . . . . . . . . . . 79

Total N Yield of Pasture and Estimation of N2 Fixation . . . . . . . . . . . . . . . . . . . . . . . . . 82

Crude Protein Content and Other Forage Quality Factors . . . . . . . . . . . . . . . . . . . . . . . . . . . 84

Botanical Changes of Pasture . . . . . . . . . . . . . . . . . . . . . 85

Plant Survival Count . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86

Leucaena Plant Height and Starter-N. . . . . . . . . . . . . . . 86

Shoot Height and Number of Branches . . . . . . . . . . . . . . . 87

CHAPTER 6 SUMMARY AND CONCLUSIONS . . . . . . . . . . . 89

LITERATURE CITED . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93

APPENDIX

A Diagrams . . . . . • . . . . . . . . . . . . . . . . . . . . . . . . . . 104

B Additional Tables . . . . . . . . . . . . . . . . . . . . . . 107

vii

LIST OF TABLES

TABLE

1 Mechanical and Chemical Analyses of Serdang Sandy Loam Soil . . . . . . . . . . . . . . . . . . .

2 Survival of Stylo Plants during Establishment Stage . . . . . . . . . . . . . . . . . . . . . . .

3 Annual Dry Matter Yields of Pasture Species in 1986 and 1987 . . . . . . . . . . . . . • . . . . . . . . . . . .

4 Annual Dry Matter Yields of Component Pasture Species and the Leaf to Stem Ratio

Page

33

49

60

of Leucaena . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61

5 Annual Crude Protein Content , N Concentration and in-vitro Dry Matter Digestibility ( IVDMD ) � . . . . . . . . . . . . . . . . . 69

6 Annual N Accumulation of Pasture Species in 1986 and 1987 . . . . . . . . . . . . . . . . . . . . . . . . . . . 71

7 Annual N Accumulation of Component Pasture Species and the Estimation of N2 Fixation by Legumes . . . . . . . . . . . . . . . . . . • . . . . . . . . . . . . . 73

8 The Effects of N Fertiliser Application and Grass-legume Combinations on Mineral Composition of Forage Plants . . . . . . . . . . . . . . 76

9 The Effects of N Fertiliser Application and Grass-legume Combinations on Soil Chemical Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78

10 Dry Matter Yield of Maize ( g per plot ) . . . . . 108

1 1 Leucaena Plant Height ( cm per plant) Measured at 4-weekly Interval during Establishment Stage . . . . . . . . . . . . . . . . . . . . . . . 109

12 Leucaena Shoot Height ( cm per plant ) Measured at 12-weekly Interval before Defoliation . . . . . . . . . . . , . . . . . . . . . . . . . . . . . . . . 110

13 Number of Branches of Leucaena per Plant Measured at 12-weekly Interval before Defoliation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 1 1

viii

14 Dry Matter Production of Grass , Legumes and their Mixtures in 1986 and 1987 . . . . . . . . 1 12

15 Mean Leaf to Stem Ratio of Leucaena in 1986 and 1987 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 1 3

16 Total N Accumulation of Grass , Legumes and their Mixtures and the Estimation of N2 Fixation by Legumes in 1986 . . . . . . . . . . . . . . . . 1 14

17 Total N Accumulation of Grass , Legumes and their Mixtures and the Estimation of N2 Fixation by Legumes in 1987 . . . . . . . . . . . . . . . . 115

18 Soil pH of Different Treatments in 1986 and 1987 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 1 6

ix

LIST OF FIGURES

FIGURE Page

1 Monthly Rainfall at Experimental Site During 1986 and 1987 . . . . . . . . . . . . . . . . . . . . . . . . 46

2 Dry Matter Yield ( g per plot) of Maize in the Soil Heterogeneity Experiment • • • . . . . . . . . . . . . 47

3 Plant Heights of Leucaena in Pure Swards and Mixtures Measured Every 4-weekly over 9 Months of Growth . . . . . . . . . . . . . . . . . . . . . . . . . . 50

4 Shoot Heights of Leucaena after 12 Weeks Regrowth over 20 Months . . . . . . . . . . . . . . . . . . . . . 52

5 Number of Branches of Leucaena after 12 Weeks Regrowth over 20 Months . . . . . . . . . . . . . . . . . . . . . . 53

6 Seasonal Dry Matter Yield of Signal Grass after 6 Weeks Regrowth over 21 Months . . . . . . . . 55

7 Seasonal Dry Matter Yield of Pure Leucaena and Stylo after 12 Weeks Regrowth over 21 Months . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56

8 Seasonal Dry Matter Yield of ( a ) Signal Grass +Stylo and ( b ) Signal Grass+Leucaena Mixtures over 21 Months . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57

9 Seasonal Dry Matter Yield of ( c ) Signal Grass +Stylo+Leucaena Mix!yres and ( d ) Signal Grass +Leucaena+100 kg ha Starter-N over 21 Months . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58

10 Seasonal Changes in Botanical Composi tion of Pasture Species in Various Mixtures . . . . . . . 64

x

LIST OF PLATES

PLATE

1 Stylo in Pure Swards after 12 Weeks

Page

Regrowth , 36 Weeks after Planting . . . . . . . . . . . 65

2 Stylo in Pure Swards after 12 Weeks Regrowth , 64 Weeks after Planting . . . . . . . . . . . 66

3 Leucaena Forming a Good Combination with Signal Grass after 12 Weeks Regrowth, 64 Weeks after Planting . . . . . . . . . . . 67

xi

Abstract of the thesis submitted to the Senate of Universiti Pertanian Malaysia in partial fulfilment of ;the requirements for the Degree of Master of Agricultural Science .

SEASONAL DRY MATTER PRODUCTION AND NITROGEN FIXATION OF LEUCAENA (LEUCAENA LEUCOCEPHALA) AND STYLO (STYLOSANTHES

GUIANENSIS ) IN PURE SWARDS AND IN ASSOCIATION WITH SIGNAL GRASS (BRACHIARIA DECUMBENS )

Supervisor

Co-supervisor

Faculty

By

AMINAH BT . HJ. ABDULLAH

January, 1989

Assoc . Professor Dr . Wan Mohamad Wan Othman

Assoc . Professor Dr . Hj. Zulkifli Hj. Shamsuddin

Agriculture

An experiment was conducted to study the effects of

rates of fertiliser nitrogen (N) and grass-legume

associations on seasonal and annual dry matter production

and forage quality factors of signal grass ( Brachiaria

decumbens). This study was also designed to es timate the

amounts of N2 fixed over the first two years of

establishment by pure stands of leucaena ( Leucaena

1eucocephala cv. ML 1 ) and stylo ( Stylosanthes guianensis

cv . Schofield ) or their mixtures with signal grass .

xii

Leucaena and s tylo were either grown in pure swards

or mixed in various combinations wi th signal grass

unfertilised with N . Dry matter production from legume-

based pasture was compared with signal grass fertilised

with urea at 0, 200, 400 , 600 or 800 kg N ha- 1yr-1

Signal grass responded markedly to N-fertiliser

applica tion, with the highest yield of 18,039 kg dry

matter -1 -1 ha yr ( at 800 - 1 -1 kg N ha yr ) compared with

7 , 385 kg dry

ha- 1yr - 1) .

matter -1 -1 ha yr for the control (0 kg N

The inclusion of leucaena in signal grass

pastures resulted in a substantial increase in total dry

matter production and total N yields compared with the

control . The total dry matter yields of the grass+leucaena

mixtures ranged from 12,223 to 12,690 kg - 1 - 1 h a yr

equivalent to the yield of signal grass fertilised with -1 -1 200 kg N ha yr The inclusion of s tylo or the addition

-1 of 100 kg N ha starter-N to the grass+leucaena mixtures

had no significant effects on the growth of leucaena or

the total dry matter yield of the grass-legume mixtures.

In grass-legume mixtures, the total dry matter and N

yields of legumes were markedly reduced compared wi th

those of leucaena ( or s tylo) in pure stands . Unlike

leucaena , the productivity of s tylo in pure stands or

s tylo component in mixtures declined with time.

xiii

300 ,

The estimated amounts of N2 fixed by leucaena were

-1 -1 240 , 155 and 88 kg N ha yr in pure stands , in

mixtures with signal grass , in signal grass+stylo -1 combination and in signal grass+100 kg ha s tarter-N ,

- 1 -1 respectively . Stylo in pure swards fixed 23 kg N ha yr

but in association with signal grass or with signal grass+

leucaena , N2 fixation by stylo increased to 37 and 45 kg N -1 -1 ha yr respectively . The higher amount of N2

apparently fixed by stylo in the mixtures was probably due

to the poor stylo survival in the pure swards .

In general , the N concentrations of leucaena and

-1 stylo were 3 . 8 and 2 . 8 g 100 g , respectively . In N-

fertilised grass , the N concentration and crude protein

content increased with increasing rates of fertiliser

application . The maximum N concentration was 2 . 2 g 100 g-l

at 800 kg N ha -l

yr-l In legume-based pastures , the N

concentration and crude protein content of signal grass

component were unaffected by the legume association . The

various treatments had little effect on the in-vitro dry

matter diges tibility , mineral concentrations , forage and

soil chemical properties .

The applications and implications of this study are

discussed with reference to forage management and

production in the humid tropics .

xiv

Abstrak tesis yang dikemukakan kepada Senat Universiti Pertanian Malaysia sebagai memenuhi sebahagian daripada keperluan untuk Ij azah Master Sains Pertanian

PENGELUARAN BAHAN KERING SEMUSlMAN DAN PENGlKATAN NITROGEN OLEH PETAl BELALANG (LEUCAENA LEUCOCEPHALA) DAN

STILO ( STYLOSANTHES GUIANENSIS) OITANAM BERASINGAN DAN DALAM CAMPURAN RUMPUT SIGNAL (BRACHIARIA DECUMBENS)

Penyelia

Penyelia bersama

Fakulti

Oleh

AMINAH BT. HJ. ABDULLAH

Januari, 1989

Profesor Madya Dr . Wan Mohamad Wan Othman

Profesor Madya Dr . Hj . Zulkifli Hj . Shamsuddin

Pertanian

Satu percubaan telah dilaksanakan untuk mengkaj i

kesan beberapa aras pembaj aan ni trogen (N) dan campuran

rumput-kekacang terhadap pengeluaran bahan kering tahunan

dan . pada setiap pemotongan serta faktor kualiti foraj

rumput signal (Brachiaria decumbens ) . Kajian ini juga

bertujuan untuk menganggarkan jumlah pengikatan N2 oleh

petai belalang ( Leucaena leucocephala kul ti var ML 1) dan

stilo (Stylosanthes guianensis kultivar Schofield) yang

di tanam secara tunggal dan campuran dengan rumpu t signal

dalam masa dua tahun percubaan .

xv

Petai belalang dan stile ditanam sama ada secara

tunggal atau bercampur dengan rumput signal yang terdiri

daripada beberapa kembinasi tanpa pembajaan N. Pengeluaran

bahan kering pastura yang berasaskan kekacang dibandingkan

dengan rumput signal yang diberi pembajaan N ( dalam bentuk

urea) pada aras 0 , 200 , 400 , -1 600 dan 800 kg N ha

setahun .

Rumput signal bertindakbalas secara berkesan terhadap

pemberian pembaj aan N dengan hasi! yang tertinggi sebanyak

18, 039 kg bahan

-1 ha setahun)

-1 kering ha

dibandingkan

setahun ( pada aras 800 kg N

dengan 7 , 385 kg bahan kering -1 -1 ha setahun bagi petak kawalan ( 0 kg ha setahun) .

Campuran petai belalang dengan rumput menghasilkan

pertambahan dalam pengeluaran jumlah bahan kering dan N

berbanding dengan petak kawalan . Jumlah hasil bahan

kering bagi campuran rumput+petai belalang berada di

-1 antara 12,223 dan 12 , 690 kg ha setahun , setara dengan

hasil rumput signal yang diberi pembaj aan N sebanyak 200 -1 kg N ha setahun . Campuran stile atau pemberian 100 kg N

-1 ha sebagai N pemula kepada campuran rumput+petai

belalang tidak memberi kesan yang ketara terhadap

pertumbuhan petai belalang atau jumlah hasil bahan kering

campuran rumput+kekacang. Dalam campuran rumput+kekacang ,

jumlah bahan kering dan jumlah N telah berkurangan dengan

berkesan berbanding dengan petai belalang ( atau stile)

xvi

yang ditanam secara tunggal . Pengeluaran s tilo dalam

petak tunggal atau pengeluaran komponen s tilo dalam

campuran dengan rumput berkurangan mengikut masa, tidak

seperti petai belalang .

Jumlah

dianggarkan

pengikatan N2 sebanyak 300 ,

oleh

240 ,

petai

155

belalang adalah

- 1 dan 88 kg N ha

setahun masing-masingnya dalam petak tunggal , campuran

dengan rumput signal , dengan rumput signal+stilo dan

dengan rumput -1 signal+100 kg N ha sebagai N pemula.

-1 Stilo dalam petak tunggal mengikat 23 kg N ha setahun ,

tetapi dalam campuran bersama rumput atau dengan

rumput+petai belalang , pengikatan N2 masing-masingnya

-1 bertambah kepada 37 dan 45 kg N ha setahun . Pengikatan

N2 yang nampaknya lebih tinggi oleh s tilo di dalam

campuran rumput dan rumput+petai belalang , mungkin

disebabkan oleh pertumbuhan stilo yang kurang baik dalam

petak tunggal .

Pada amnya , kepekatan N dalam petai belalang dan

stilo masing-masingnya sebanyak 3 . 8 dan 2 . 8 g 100 g-1 .

Pada rumput yang diberi pembaj aan N , kepekatan N dan

kandungan protein kasar bertambah dengan meningkatnya

kadar pembaj aan . Kepekatan N yang tinggi diperolehi -1 . -1 sebanyak 2 . 2 g 100 g pada kadar pembaj aan 800 kg N ha

setahun . Bagi pastura yang berasaskan kekacang , kepekatan

N dan kandungan protein kasar rumput signal tidak

xvii

dipengaruhi oleh campuran kekacang yang ditanam bersama­

sama rumput tersebut .

Kesemua perlakuan yang dijalankan tidak memberi kesan

terhadap penghadaman bahan kering secara in-vitro .

kepekatan mineral dalam foraj dan sifat kimia tanah .

Penggunaan

dengan memberi

dan implikasi kajian

perhatian terhadap

pengeluaran foraj di kawasan

xviii

ini dibincangkan

pengurusan dan

tropika lembap .

CHAPTER 1

INTRODUCTION

Commercial livestock production in Malaysia has been

mainly dependent on nitrogen ( N) -fertilised grasses , a

system that allows maximum intensification of pasture

production . The application of high rates of N fertiliser

is necessary to maintain high productivity of fodder

grasses in this country (Keeping, 1951 ; Ure and Mohamad,

1957; Balachandran , 1969 ; Tan and Pillai, 1975; Tham,

1980) . However , manufacturing processes of fertilisers

are closely related to the petro-chemical industries , and

for N fertiliser alone the energy required accounted for

about 94% of the energy used in manufacturing all the

fertilisers consumed in developing countries ( Halliday,

1982) .

About 90% of the ruminant animals in this country are

reared by smallholders . Therefore , to encourage and to

develop better small-scale farming together with the

present shortage of energy supply , it is worthwhile

considering legume-based pastures which need relatively

low fertiliser inputs .

1

2

Systematic introduction and evaluation of pasture

grasses and legumes in Malaysia commenced in 1972 (Wong

et al . , 1982 ) . One of the pasture grasses with agronomic

potential is signal grass ( Brachiaria decumbens ) ( Graham ,

1951 ; Anon , 1975 ; Loch , 1977 ) . Being a vigorous and

aggressive grass , it is found to be too competitive for

most trailing legumes but it can be utilised in

combination with rows of leucaena ( Leucaena leucocephala)

( De Gues , 1977 ) or stylo (Stylosanthes guianensis)

(Ng , 1976 ) .

Legumes in symbiotic association with Rhizobium have

the ability to fix N2 from the atmosphere . Legumes have

been shown to increase soil N content , and the organic

matter status of the soil but reduce soil compaction and

soil moisture loss ( Anon . , 1984 ) .

Numerous studies have been carried out highlighting

dry. matter and animal production of N-fertilised grass

pas tures , but there is s till a lack of information in

literature on the productivity of legume-based pastures

especially on signal grass+leucaena , signal grass+stylo or

signal grass+stylo+leucaena mixtures . In Malaysia.

research data on a comparative study on dry matter

production of N- fertilised signal grass and legume-based

signal grass are also limited . This s tudy aims to

investigate the effects of fertiliser N and legumes ( s tylo

3

and leucaena) on dry matter production and botanical

composition of the pastures , and consequently their

effects on soil fertility . Secondly , this study attempts

to estimate and compare the amounts of N2 fixed by stylo

and leucaena in pure swards and in signal grass mixtures

during the first two years of establishment .

CHAPTER 2

REVIEW OF LITERATURE

Sources of Nitrogen (N) for Grassland Production

Various sources of N for growth of pastures are

available ( Whiteman et al . , 1974 ) : N from soil , N2 fixed

by microorganisms associated with some tropical grasses , N

from industrial synthesis ( fertiliser N) and N2 from

fixation by legumes ( symbiotic N2 ) . Fertiliser N and

symbiotic-N2 are the primary sources of N in pasture

production .

Nitrogen Requirements and its Absorption by Plants

Nitrogen is essential for plant growth as i t is a

consti tuent of all proteins and nucleic acids and hence of

all protoplasm . Nitrogen is also a constituent of

chlorophyll and it is , therefore , important for

photosynthesis , growth and reproduction . Nitrogen

concentrations in plants normally range from 0 . 2 to 4 . 2%

depending upon the species ( 1 . 9 to 4 . 2% as in the

legumes ) , plant part and physiological age ( Chapman and

Pratt , 1961 ) . Nitrogen is highly demanded by pasture

4

5

grasses due to the higher photosynthetic rates of grasses

than the dicotyledonous field crops ( Kalpage , 1977 ) .

Nitrogen deficiency exerts a marked effect on plant

growth and yield . Plants remain s tunted , all the leaves

assume a uniform pale yellow colour and senescence of

leaves occurs . An excessive application of N , however ,

induces a luxuriant development of the subaerial

vegetative organ but the root systems remain small .

Tissues from these plants are spongy , weak and dark green

(Marschner , 1986 ) .

In soil , N occurs mainly in two forms , the readily

available inorganic N ( nitrate , ammonium or amides as in

fertiliser urea) or the slowly available organic

compounds . Nitrogen uptake by plants is mainly in the

form of NH + 4 and N03 ions ( Gilbert , 1984 ) . Nitrogen

reserve held in organic forms are firstly mineralised , the

ammonia released being converted by the soil bacteria into

nitrates . Since plants continuously withdraw mineral N

from soil , more organic matter is degraded to release

organic N and restore the N balance ( Ismunadj i and

Makarim , 1987 ) .

Nitrogen Fertiliser and its Availability

Selection of the mos t appropriate source for N

fertiliser depends on the unit cost of N , the need and

6

effectiveness of the fertiliser ( Gilbert , 1984) . The

availability of soil N should also be considered in

deciding the rate of fertiliser N to be applied since N

use efficiency is low at high soil N levels ( Ismumi.dj i and

Makarim , 1987) . Soil water and temperature also influence

the N use efficiency by affecting the rates of

mineralisation and immobilisation of soil N ( Jansson and

Persson, 1982) .

Among the ni trogenous fertilisers commonly used for

pasture production are ammonium sulphate ( 21% N), urea

( 46% N), ammonium nitrate ( 26% N) and calcium ammonium

nitrate ( 26% N) . Ammonium nitrate and calcium ammonium

nitrate, which + supply N both NH4 -N and N03--N can ,

therefore, be considered as preferred nitrogenous

fertilisers for pastures ( Kalpage , 1977) . When these

fertilisers are applied to moist soils, N can be directly

absorbed by the plants ( Gilbert , 1984) . However, the unit

cost of N in both of these fertilisers is more than in

urea (Kalpage, 1977) , the cheapest source of N ( Gilbert,

1984) and hence urea is used extensively .

Urea fertiliser, however , cannot be absorbed directly

and must be transformed into the NH4+ and N03 forms prior

to absorption by plants . Urea , in soil, is very quickly

hydrolysed to ammonium carbamate and finally to ammonia

and carbon dioxide in the presence of urease , an enzyme