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THE EFFECTS OF SHADING AND DEFOLIATION ON THE NODULATION AND NITROGEN FIXATION OF WHITE CLOVER (TRIFOLIUM REPENS L.)
A thesis
presented in partial fulfilment of
the requirement for the
degree of Master of Agricultural Science
at
Massey University
Alexander Cheong Ping Ch•
1971
In a gla.ashoue experiment, aing1e plants of ten-weev..s-old white cloYer (IrifolLwn repen• L.) were aubjeeted to two levels of ehading and two levels of detoU.ation. Plant growth, nodulation aud nitrogen fixation parameters were collected on eix eequen~ial harvests over four weeks.
Losses of roots and nodul.ee reaul. ti.ng from the treatments were probab1y due to a reduction in photoaynthate supply. Decreases in nodul.e number and hence nodule dry weight per plant were due to nodule decay, sloughing off and non-production, and were related to the losses in root dry weight. Total nodule numbers on both •control' and
' treated• plan ta increased with time, du mainly to increases in numbers of medium aised (1-31UD) nodul.ea. Reduction in nodule weight per plant in the •treated' planta wae later reflected in a lower mean nodule weight.
Severe defoliation caused degradation of the pink pigment, leghaemoglob in, an effect whieh was aeen in leas than three daya from treatment.
It also led to a temporary marked d•crease in the nitrogen fixing capability of the nodule• a• measured by the acetylene reduction assay. Recovery of normal act1Tity by the m.trogen fixing system in
the defoliated planta took about ten daya.
The auitability of acetylene reduction aasay for a short term experiment, and the relat1onanip oetwee11
and nodule coiour are brie
n1
diacuased.ACKNOWLEDGEMENTS
It is a great pleasure to acknowledge the stimulation and wise counsel of my eupervieor Mr. A.G. Robertson in all facets of this study. I am also grateful to Professor B.R. Watkin for his discussion and guidance which initiated me into this most rewarding field of research.
I acknowledge the assistance given to me by the following:•
Professor B.I. Hayman, Dr. B.S. Weir and Mr.
G . c .
Arnold forstatistical analysis.
Professor R.E. Munford and Miss N. Gordon for guidance in computer operation and also to Professor Munford for permission to use his
general statistical program (STATCS).
Dr. J.C. Hawke for teaching me the gas chromatogram technique. Dr. w.B. Silvester of Auckland University who kindly taught me the acetylene· reduction technique in his laboratory.
Professor R.C. Earle, Dr.
c.v.
Fife and Professor D.S. Flux for permission to use their laboratories.Mr. R.K. Reekie for making all the glassware used in this experiment.
I would like to thank the staff of Massey Library, D.S.I.R. Library, Central Store, Photography Unit and the Printery for prompt service. I would also like to thank Miss
s . Y .
Geh, now of Botanical Gardens,Singapore, for technical assistance, and to Mrs. J. Humprhies for the
The assistance and discussions given by Dr. G.w. Butler, Dr. P.C.
Barclay, Mr. R.M. Greenwood and Mr. P. Evans of D.S.I.R. Palmerston North are gratefully acknowledged.
I would like to record my gratitude to Dr. R.J.S. Clements for his sincere and critical discussions on the manuscript, any errors remaining in this theaia are entirely mine.
Finally, I thank my wife, Jeruay for her patience, encouragement and interest throughout thi.s study.
Financial awards from the following Scholarships are gratefully aoknowledged:-
Colombo Plan Scholarship Massey Scholarship
Alexander Hurle7 Scholarehip.
TABLE OF CONTENTS
List of Figures, Tables and Diagrams
General Introduction
Chapter I Review of Literature 1 Nodulation
2 Nodule functions
3 Factors affecting nodulation and nitrogen fixation
Chapter II Experimental 1 Materials
2 Experimental
3 Preparation for experiment 4 Growing of experimental plants 5 Conduct of the actual experiment 6 Preparation of material and method
of analysis
7 Statistical analysis
Chapter III Results 1
2 3 Chapter IV
1 2 3
Plant growth Nodulation
Nitrogen fixation
Discussion Plant growth Nodulation
Nitrogen fixation
Conclusion Bibliography Appendices Plates
Page
ii
l
2 7 14
29 30 34 36 38 38 42
44 50 68
81 83 87
92
Figures
II.1
II.2
III.1.1 III.1.2.1 III.1.2.2 III.2.1 III.2.2 III.2.3 III.2.4 III.2.5
III.2.6 III.2.7
III.2.8 III.2.9 III.2.10 III.3.1 III.3.2 III.3.3 III.3.4
III.3.5 III.3.6 111.3.7
LIST OF FIGURES1 TABLES AND DIAGRAMS
Calibration of light meter reading against standard Eppley pyrheliometer Average weekly maximum, minimum and
noon air temperaturee, pot temperatures and relative humidity
Average leaf size (L X C interaction) Dry weight measurements (light treatment) RGR
Dry weight meaeurements (defoliation treatment) RGR
Nodule numbers (light treatment)
Nodule numbers (defoliation treatment) Nodule number (large) L X C interaction Three dimensional graphs of nodule number per inch
Number of 'pink' and 'green• nodules per inch
Nodule dry weight per plant
Three dimensional graphs of nodule weight per inch
Average dry weight per nodule Number of nodules per 100 mg root Nodule dry weight per 100 g root Percentage nitrogen (light treatment)
Percentage nitrogen (defoliation treatment) Plant nitrogen content (light treatment) RRNA
Plant nitrogen content (defoliation treatment) RRNA
Hg nitrogen fixed per gram nodule p r day
Acetylene reduction a.asq (time course)
Effect of shading and defoliation on the rate of
c
2u
2 --c
2u
4 reduction permg nodule per hour (fresh weight)
Page
33
33
47
49
49 53 54 55
57
60-61
62 63 66 67 71 72 73
76
19
8o
Tables
II.1 III.1.1
III.1.2 III.1.3 III.3.1 III.3.2
Diagrams
1.
2.
3.
4.
Light intensity readings
Total leaf area and leaf number per plant
Dry weight measurements
Top to root ratios Nitrogen contents
Comparison of regressions between log10 plant nitrogen content and nodule dry weight
General layout of glasshouse Carlson scale
System for numbering root segments
Chromatogram example
appendix
appendix appendix
Page
47
48 48 7077
31 1I.3 II.8 II.9
1
GE ERAL INTRODUC!IOJI
1!he ability of the legwne-Rhisobium ayabioaie to fix at oapherio nitrogen, hence contributing towarcla the maintenance of soil fertility 1s well recogniaed. Although increasing usage of mineral nitrogen is eYident in agricultural practices overaeae (Watkin, Williama 1970), in New Zealand legume ni uogen ia still by far the moat iaportant source of Di trogen in grassland farming.
itrogen fixation in a ferti.le ryegraes-white clover association has been estimated to yield aa auch aa
550 lb
N per acre per annum(Seara 1953), and it has been emphasised that for maxiaum benefit to the grass compoaent in a mixed awar4 the white clover should be periodically defoliated and
ha••
ample light for regrowth (Butler, Greenwood & Soper 1959).The present study examines the effects of defoliation and ahadi.ng on nodulation and nitrogen fixation in white clover.
