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