A study of spring grazing management effect on summer-autumn pasture and milk production of perennial ryegrass x white clover dairy swards : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy (Ph.D.) in Pasture Agronomy at Massey University

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.

AUTUMN PASTUR E AND MILK PRODUCTION OF PERENNIAL RYEGRASS x WHITE CLOVER DAI RY S WARDS

A thesis presented

i n partial fulfi l ment of the requirem ents for the degree of D octor of Philosophy (Ph . D.) in

Pasture Agronomy at Massey U niversity.

Sila Carneiro da S i lva 1994

ABSTRACT

Evidence generated at Massey University demonstrated the impo rtance of the mani pulatio n of ryegrass reproductive g rowth duri ng spri ng to pasture productio n . It showed that lax g razing of pastu res duri n g spring followed by hard g razi ng at the time of anthesis could result in an e nhancement of sum me r-autumn herbage production, associated with an e n hanced tillering activity of ryeg rass plants. Such g razi ng management was call ed "late control", and it was thought to be an option for enhancing pasture production, particularly in dairy farms, where conditions for manipulati ng reproductive swards would be most favou rable. Thus, the objectives of this study were (i) to evaluate the effects of this l ate control spri ng grazing management on su m me r-autumn herbage production and botanical com position of ryegrass­

white clover dairy pastures, and (ii) to investigate the consequences of such a g razin g management strategy on pasture quality, herbage i ntake and milk production by dai ry cows.

Three field experi ments are reported. The fi rst two were sward-based experiments whose results were used to plan and set up the third experi ment, which i nvolved evaluation of both sward and ani mal effects.

The results from Experi me nt 1 (October 1 990 to April 1 99 1 ) and 2 (October 1 99 1 to A pril 1 992) confirmed the expectation s of e nhanced spri ng and sum mer-autumn herbage accumulation from a late control g razing management ove r the s pring time. An average i ncrease in production of the o rder of 750 Kg D M/ha (25%) was obtai ned fro m October to November, and of 1 .0 t DM/ha (20%) was obtain ed from January to Apri l in both years, with ryegrass accum ulation being e n hanced in Experiment 1 and white clover accu m ulation enhanced in Experi ment 2. Evidence gathered about tilleri ng activity was inconcl usive, although it showed that tillers produced under the

late control s pri ng g razing management were bigger than those produced u nder the conventional hard g razing management. White clover res ponse was variable from year to year. It was concluded that the ti ming as well as the i ntensity of executio n of the late control were very im portant. Late control should be executed at the time of anthesis of the re prod uctive develo pment of ryeg rass plants (late Novem ber-early Decem ber), and the rem oval of seed heads and re productive stems should be g radual , over two o r three successive grazing cycles.

Simulation of the im plementation of this late control g razi ng management on a farm basis was then performed, based o n the results from Ex pe riments 1 and 2, in order to gai n an overview about possible practical i m plications for farm practice. The models showed that the pre paration of pastu res to achieve the re productive stage prio r to late control was feasible and would not i m ply any decrease in the feeding level of dairy cows. However, more i nformation was n ecessary o n how to execute late control and whether o r n ot the i ncreased summer-autumn herbage accumul ation could be converted to milk production.

Further evaluation of late control g razi ng in E x periment 3 (October 1 992 to A pril 1 993) revealed that i ncrease in s pring herbage accum ulation by 1 000 Kg DM/ha (25%) was a 'consequence of the re productive g rowth of peren nial ryegrass plants, which caused a decrease i n the digestibility of the herbage consu med from 78% to 75% due to the increased contents of senescent and g rass ste m material in the sward. On the other hand, i ncreased summer­

autu mn herbage accumulation ( 1 000 Kg DM/ha, 25%) after l ate control was due to e n hanced accu mulation of both ryegrass and white clover. The digestibility of the herbage was restored soon after late control. Des pite the lower digestibility of re productive swards duri ng the control period, no significant reduction i n the herbage intake of dairy cows was detected i n com parison with animals g razi ng leafy and vegetative swards. However, the use of forage conservation to aug me nt g razing pressure duri ng the late control

phase proved to be more effective than a grazing only strategy, si nce a large proportion of senescent material was allowed to form u nder those circumstances. The i ncrease in s u m mer-autum n herbage accumulation was associated with an i ncrease in milk solids yield per cow of the o rder of 10%, with aro u nd 25 Kg milk-fat being o btai ned from the e xtra ton ne of dry matter accumulated per hectare i n late control pastures.

It is concluded that the l ate control spring g razi ng management of perennial ryeg rass -white clover pastu res can be used as an o ption to enhance pasture production in dairy farms, particularly duri n g the sum me r -autu m n peri od, and that this i ncreased herbage accumulation can b e effectively converted to milk solids yield. The i mplementation of this grazi ng strategy i nto a farm context and its implications for farm practice are bri efly discussed.

ACKNOWLEDG EM ENTS

Thanks are due to my chief supe rvisor, Professor John Hodgson , and my co-supervisors, Mr Parry N . P. Ma tthews, Dr Cory Matthew and Associate Professor Colin W. Holmes, for their patience, e ncouragem ent, i nterest , support and assistance th roug hout this project. Special thanks are due to P rofessor John Hodgson who went far beyond the call of duty as a supervisor to e nsu re my wife and I were appropri ately settled and assisted .

The project was developed at one of the U niversity Farms, the No 4 Dairy Farm, and because of that thanks are due to the Farm's Ad ministration staff, particularly Mr Gerard Lynch (former dairy farms superviso r) , M r David G rant, M r Alastair MacDonald and Mrs Fiona Cayzer; and to the farm staff membe rs , Mr Mark Power, Mr Peter Crosbie, Mr Ben Finlay, and M rs Joanne Stent.

The help and support from field and laboratory tech nicians is also acknowledged. These helpers included Mr Terry Lynch, Mr Mark Osborne, M r Gary Evans, M rs Jackie Harrigan, M s Louise Saunders, M r Paul Sharp, M rs Frith Brown , Mrs Cally Mckenzie, Ms Rosemary A. Watson and Mirian Hendri ks.

The New Zealand Ministry of Foreign Affairs and Trade, the Dairyi ng Research Corporation Li mited, and Funda c;ao de Amparo a Pesquisa do E stado de S ao Paulo (Brazil ) and E.S.A. "Luiz de Quei roz" (Brazil ) are thanked for provision of post-g raduate stipend and financial assistance towards the costs of this study.

Thanks are finally due to my wife, Ana Estela, for her patience, e ncouragement and support throug hout our stay i n New Zealand.

TABLE OF CONTENTS

ABSTRACT ^{. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .} ii

ACKNOWLEDGE ME NTS . . . v

TABLE OF CONTE NTS . . . .. . . vi

LIST OF TABLE S . . . . . xvi

LIST OF FIGU RE S . . . . . xxi

Chapter 1 : I ntroduction and Objectives . . . . . 1

Chapter 2: Literature Review ^. . . . . . 4

2 . 1 . Introduction and ove rview . . . . . 4

2.2. Grassland farming systems and seasonality of pastu re production ^. . . . . . 5

2.3. Characteristics of perennial ryegrass and white clover plants . . . . . 7

2.3. 1 . Perennial ryeg rass (Latium perenne L.) ^{. . . . . . .} . . 7

2.3. 1 . 1 . Plant biology ^. . . . . . 7

2.3. 1 .2. Plant responses to g razing management . . 1 0 2.3.2. White clover (Trifolium repens L.) . . ^{. . . . . . . . . . .} 1 3 2.3.2. 1 . Plant biology . . . . . 1 4 2.3.2.2. Plant responses to g razi ng management . . 1 6 2.3.3. Perennial ryeg rass and white clover plants g rown in mixtures ^{. . . . .} . . . . ^..^{. .}.^{. . . . . . . . .} . ^{. . . . .} 1 9 2.4. Spri n g grazing manageme nt of perennial ryegrass/white clover pastu res . . . . . 21

2.4. 1 . Tiller populations and sward productivity ^{. . . . . . . .} 23

2.5. Sward conditions and herbage utilisation by the g razing ani mal ^{. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .} 28

2.5. 1 . Herbage i ntake under g razing ^. . . . . . 29

2.5.2. Ani mal behaviour under g razing . . . 3 1

2.6. Pastu re production and the productivity of dairy systems . . . 33

2.6. 1 . Pasture control and feedin g level of dai ry cows . .. 34

2.6.2. Grazing management systems and dairy g rasslands productivity . . . . . . 36

2.7. Implications of the agronomic data for dai ry production systems . . . 41

2 .8. Conclusion . . . . . 44

Chapter 3 : Theoretical Hypothesis and Experimental Prog ram me . . . . . 45

Chapter 4: Influence of Spri ng G razing Management o n Su mmer­ Autumn P roduction of Perennial RyegrasslWhite Clover Dai ry Pastures . . . . . 47

4. 1 . Introduction . . . 47

4.2. Experi mental . . . 49

4.2. 1 . Objectives . . . . . 49

4.2.2. Site . . . . . 49

4.2.3. Experimental design . . . . . 5 1 4.2.4. Experimental treatments . . . . . 52

4.2.5. Measurements . . . . . 54

4.2.5. 1 . Herbage accu mulation and components . . 54

4.2.5.2. Ryeg rass tiller demography and dynamics . . . 54

4.2.5.3. Species population densities . . . 57

4.2.5.4. Soil fertility . . . 57

4.2.6. Statistical analysis . . . ^. . . . 58

4.3. Results . . . . ^. . . . ^. . . . 59

4.3. 1 . Ryeg rass tiller demog raphy and dynamics . . . . . 59

4.3.2. Grass tiller and clover stolon/node population . . . . 66

4.3.3. Dry matter productio n and herbage accumulation rates . . . . . 73

4.3.4. Relationship between the measured variables

accordi ng to Canonical Discri m inant Analysis . . . . 84

4.4. Discussion . . . . . 89

4.4. 1 . Research tech niques . . . . . 89

4.4.2. Ryegrass tiller demog raphy, dynamics and population . . . . . 90

4.4.3. White clover stolon/node population . . . 92

4.4.4. Herbage d ry matter accu mulation . . . ^. . . . 94

4.4.5. Herbage components accumulation . . . . . 95

4.4.6. Ryegrass:clover balance . . . . . 97 4.5. Summary . . . 1 01

Chapter 5 : Feasibility of the Late Control Spri ng G razing Management

for Season al Dai ry Systems . . . 1 02 5. 1 . Introductio n . . . 1 02 5.2. Simulations of late control g razing i n a farm condition . . . 1 03 5.2. 1 . Manawatu downland areas . . . 1 05 5.2.2. Experimental site . . . 1 07 5.3. Discussion . . . ^. . . . 1 09

Chapter 6 : Spring G razi ng Management Effect on Summer-Autu mn

Pasture and Milk Production of Mixed Dairy Swards . . . 1 1 1 6. 1 . Introduction . . . ^{. .} . ^. . . . 1 1 1 6.2. Experi m ental . ^. . . . ^. . ^. . . . 1 1 3 6.2. 1 . Site . . . ^. . ^. . . . 1 1 3 6.2.2. Experimental desig n . . . 1 1 5 6.2.2. 1 . Pastu re evaluations . . . 1 1 5 6.2.2.2. Ani mal evaluations . . . 1 1 5 6.2.3. Experimental treatments . . . 1 1 6 6.2.4. Measurements . . . 1 1 9 6 .2.4. 1 . Pasture responses . . . ^. . ^. . . ^. 1 1 9

6 .2.4. 1 . 1 . Herbage accu mulation and

components . ...^. . ^... . . . ^.. . ^. . ^.. 1 1 9 6 .2.4. 1 .2. Average pasture cover . . . ^{. .} . . . 1 20 6.2.4. 1 .3. Tiller dynamics . . . ^. . . ^. . 1 21 6 .2.4.1.4. Species population densities . ^{. . .} 1 22 6.2.4.2. Animal responses . . .^. . . . . ^. . . . ^..

.

. 1 23 6.2.4.2. 1 . Milk yield and com position . . . ^. . . 1 23 6.2.4.2.2. Liveweight and body condition

score of cows . . . ^. . . ^. . . ^. 1 24 6.2.4.2.3. Herbage i ntake and sward

quality . . . . ^. . . . ^{. .}. . . ^. . ^. . 1 24 6 .2.4.2.4. Grazing behaviou r . . . ^{. .} . ^. 1 26 6.2.5. Statistical analysis . . . ^. . 1 26 6.3. Results . . . ^{. .} . . . . ^. . . . ^. . . . ^. . . . 1 27 6.3.1 . Tiller dynamics . . . ^. . . . ^. . .^. 1 27 6 . 3.2. G rass tiller and clover stolon/node population ^. . . . 1 33 6.3.3. Herbage accu mulation and average pastu re

cover . . . ^. . . . . ^. . . . ^. . . . 1 37 6 . 3.4. Sward quality and herbage intake . . . ^. . .

.

1 47 6.3.5. Patterns of grazing behaviour . . ^. . . . 1 51 6.3.6. Milk yield and composition

... 153

6 .3.7. C hanges in liveweight and body condition score . . . 1 54 6.3.8. Relationship between pasture and an imal

responses according to P ri ncipal Co mponents

A nalysis . . . 1 60 6.4. Discussio n ^. . . . ^. . . . . ^. . .^. . . . 1 62 6.4. 1 . Techniques .^{. . .} . . .. . ^. . . . ^{. . . .} .

.

..^.. 1 62 6.4.2. Tiller dynamics and population . . . ^. . ^. . . . . ^. . 1 64 6.4.3. Clover stolon/node population . . . .

.

. 1 67 6.4.4. Herbage dry matter accumulation . . . ^{. .}.^.. . .. 1 68 6.4.4. 1 . Herbage dry matter composition . . . ^. . ^. . . 1 70 6.4.5. Ryeg rass:clover balance ^. . . . .^. . . . . ^{. .} . ^. 1 72

6.4.6. Herbage quality and i ntake . . . 1 74 6.4.7. Ani m a l pe rformance ^{. . .} . ^{. . . .} . ^{. . . . . . . . . . . . . .} 176 6.5. Sum mary ^{. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .} 1 81

Chapter 7 : Overall Analysis of Combined Experiments . ^{. .} . ^{. . . . . . . .} 1 82

C h apter 8 : Ove rview and Conclusions ^{. . . . . . . . . . .} . ^{. . . . . . . .} . ^{. . .} 1 85 8. 1 . Synthesis of results . ^{. .} . ^{. . . . . . . . . . .} . ^{. . . .} . ^{. . . . .} . ^. . 1 85 8.2 . Implications for farm practice i n New Zealand . ^{. . . . . . . . . .} 1 89 8.3. Further research ^{. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .} 1 9 1 BIBLIOG RAPHY ^{. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .} 1 93

Appendix 1 : Outputs of Late Control Si mulation Models ^{. . . . . . . .} . ^{. . .} 21 3

LIST OF TABLES

Chapter 4:

Table 4 . 1 . Grazi ng dates of the experi mental plots for Experime nts 1

and 2 . . . 56 Table 4.2. Levels of pH, labile phosphorus (ppm) and exchangeable

potassium (meq/1 00 g soil) of experi mental plots in Experiment

2 . . . 58 Table 4.3. Number of new tillers formed per floweri ng tiller and tiller

survival rate (TSR)(%) of the origi nal population of tagged ti llers

at each of the two tiller harvest dates of Experi m e nt 1 . . . . . 60 Table 4.4. Individual tiller wei g ht (mg) of new formed tillers at each of

the two tiller harvest dates of Experime nt 1 . . . , 6 1 Table 4.5. Total weig ht (mg) of new formed tillers per flowering tiller at

each of the two tiller harvest dates of Experi ment 1 . . . . . 62 Table 4.6. Average number of new tillers formed per parent tiller at the

fi nal harvest of Expe ri ment 2 ( 1 4 to 23 April, 1 992) . . . . . 63 Table 4.7. Individual tiller weight (mg) of new formed tillers at the final

harvest of Experiment 2 (1 4 to 23 April, 1 992) . . . 64 Table 4.8. Total weight (mg) of new formed tillers per parent tiller at the

final harvest of Expe ri ment 2 (1 4 April, 1 992) . . . 65 Table 4.9. Average number of tagged tillers per parent tiller throughout

Experiment 2 . . . 68 Table 4. 1 0. Rates of ryeg rass tiller appearance, death and survival for

the different experi mental phases in Experiment 2 . . . . . 69 Table 4. 1 1 . G rass tiller population density (tillers/m2) at the end of

Experi ment 1 (ApriI/9 1 ) and throughout Experi ment 2 . . . 70 Table 4 . 1 2. White clover stolon population at the end of each

experi ment and clover nodes density throughout Experi ment 2 . . 7 1

Table 4.1 3. Weed populatio n densities (plants/m2) throug hout

Experiment 2 . . . 72 Table 4. 1 4. Monthly herbage accu mulation rates for Experi ments 1 and

2 (Kg D M/ha iday) ^{. . . . . . . . . . . . . . . . . . . . . . . . . .} . ^{. . .} . . ^. . 74 Table 4 . 1 5. Total herbage d ry matter accumulation in E xperiments 1

and 2 (Kg D M/ha) ^{. .} . . . . . 75 Table 4. 1 6. Herbage com po nents accumulation ( Kg D M/ha) in

Experiments 1 and 2 . . . . . 76 Table 4 . 1 7. G reen dry m atter accu mulation components duri ng

Experi ment 1 (Kg DM/ha) ^{. . . . . . . . . . . . . . . . . . . . . . . . .} . ^{. .} 78 Table 4 . 1 8. Species d ry matter accumulation duri ng Experiment 2 (Kg

D M/ha) ^{. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .} 79 Table 4. 1 9. Species com ponents accu mulation ( Kg D M/ha) i n

Experiment 2 . . . 80 Table 4.20. Pre-g razing live :senescent materi al ratio for the three

experimental phases of Expe ri ment 2 . . . . . 81 Table 4.21 . Pre-g razi ng leaf:stem ratio of the g rass component of the

sward for the three experime ntal phases of Experi m e nt 2 . . . 81 Table 4.22. First canonical factor for analysis of ( 1 ) paddock and

(

2

)

treatment effects i n CDA of five variables. . ^{. .} . . . ^{. .} . ^{. .} . . . 86

Chapter 6 :

Table 6 . 1 . Rates of ryegrass tiller appearance (TAR), death (TOR) and

survival (TSR) throughout the experi mental period ^{. . . . . . . . . .} . 1 28 Table 6.2. Average nu mber of tagged tillers per parent tiller throug hout

the season ^{. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .} . ^{. . . . . .} 1 29 Table 6.3. Average nu mber per parent tiller of tillers formed duri ng the

observation period and still alive at the final h arvest of the season

(

1 8 to 30 Apri l , 1 993

)

. . . 1 3 1 Table 6.4. Individual tiller wei g ht (mg) of new formed tillers at the fi nal

harvest of the season

(

1 8 to 30 April, 1 993

)

. . . 1 32

Table 6.5. Total weight (mg) of new formed tillers per parent tiller at the

fi nal haNest of the season ( 1 8 to 30 Apri l , 1 993) . . . 1 32 Table 6.6. G rass tiller population densities (tiller/m2) throug hout the

season ^. . . . ^. . . . ^. . ^. . . . ^. . ^{. .} . ^. . 1 34 Table 6.7. Clover stolon/node popu lation densities throughout the

season . . . . ^. . . . ^. . ^. . . . 1 35 Table 6.8. Weed population densities (plants/m2) throughout the

season . . . ^. . . . ^{. .} . 1 36 Table 6.9. Monthly herbage accumulation rates (Kg D M/ha/day)

throug hout the season . . . ^{. .} . . . 1 38 Table 6. 1 0. Average pasture cover over the experimental farmlets

d u ri ng the four weeks of the control phase ( Kg DM/ha) ^. . . . 1 38 Table 6 . 1 1 . Average pastu re cover over the experi mental farm lets

duri ng the post-control phase and at dryi ng-off date

(28

April,

1 993) (Kg D M/ha) ^. . . . 1 39 Tabl e 6 . 1 2 . Herbage dry matte r accumulation ( Kg DM/ha) du ri n g the

three experi mental phases . . . ^. . . . ^. . . . 1 41 Table 6. 1 3. Pre-g razing live :senescent mate rial ratio for the three

experi mental phases . . . 1 42 Table 6. 1 4. Species d ry matter accu mulation (Kg DM/ha) during the

th ree experimental phases . . . ^. . . ^{. .} . . . 1 43 Table 6 . 1 5. Species components accumulation ( Kg DM/ha) d u ri n g the

three experi mental phases . . ^. . ^. . . . . ^{. .} . ^. . . . ^. . . . ^. . ^. . . . 1 44 Tabl e 6 . 1 6. Pre-grazi ng leaf :stem ratio of the g rass component of the

sward for the three experi me ntal phases . . ^. . . . 1 46 Table 6.17. Mai n botanical features of herbage sampled by hand

plucking simulating g razi ng i n areas protected from g razi ng by

exclosure cages from 14 to 23 December . . . 1 47 Table 6. 1 8. Nutritive value of the herbage sampled by hand p lucking of

areas protected from g razi ng by exclosure cages from 1 4 to 23

December . . . ^. . . . ^. . ^{. .} . . . ^{. .} . ^{. . . .} . . . ^{. .} . . . ^. . . ^{. .} 1 48

Table 6 . 1 9. Values o f esti mated in vivo digestibilities (%) for the d ry matter and organic matter o f extrusa samples col lected by oesophageal fistul ated cattle at either the beg i n ni ng and end o f g razi ng ^. . ^{. . . . . . . .} . . ^{. .} . ^{. . . . . . . .} . ^{. . .} . . ^{. . . . . . . . . . . . .} 1 49 Table 6.20. Estimates o f herbage i ntake (Kg/cow/day) by the

experi mental g roups of cows at both periods of measurement as

determ i ned using the chromium oxide technique . . ^. . ^{. . . . .} . ^{. .} 1 50 Table 6.21 . Time spent i n speci fic a �tivities by dairy cows g razing the

experi mental swards (hours) and their rates o f biti ng

(bites/mi nute) . . . ^{. . . . .} . . . ^. . . ^{. .} . . ^. . . ^{. . . . .} . 1 52 Table 6.22. Daily milk yield d u ri n g the farmlet study period

(Iitres/cow/day) and the cum ulative total yields for the control and

post-control phases (Iitres/cow) . . . ^. . ^. . . . ^. . . . . ^{. . .} . . . 1 55 Table 6.23. Milk composition for the three experimental treatments

d u ri ng the control and post-control phases (%) ^{. . .} . . . . ^. . . ^. . . 1 56 Table 6.24. Daily milk- fat yield during the farmlet study period

(Kg/cow/day) and the cumulative total yields for the control and

post-control phases (Kg/cow) . . . ^. . . . ^{. .} . . . ^. . . . ^. . . . . ^. 1 57 Table 6.25. Daily milk-protein yield duri ng the farm let study period

(Kg/cow/day) and the cumulative total yields for the control and

post-contro l phases ( Kg/cow) ^{. .} . . . ^{. . .} . ^. . . . ^{. .} . . . . ^. . ^. 1 57 Table 6.26. Daily milk-lactose yield during the farmlet study period

(Kg/cow/day) and the cumulat ive total yields for the control and

post-control phases (Kg/cow) . ^. . . ^. . . . ^. . . . ^{. .} . . ^. . . . ^. . . . ^. . 1 58 Table 6.27. Daily milk-solids yield duri ng the farmlet study period

(Kg/cow/day) and the cumulative total yields for the control and

post-co ntrol phases (Kg/cow) . . . ^. . . . ^. . ^. . ^. . . . . ^. . . . . ^. . . 1 58 Table 6.28. Average liveweight (Kg ) throug hout the farmlet study period

(control and post-control experimental phases) . . ^. . . . ^. . . . 1 59 Table 6.29. Average body condition score throug hout the farmlet study

period (control and post-control experime ntal phases) ^. . ^{. .} . ^{. . .} 1 59

Table 6.30 . Correlations between raw data and PC scores, and the proportio n of total variance explain ed by PCA of the combined

data set of animal and pasture responses . . . 1 61

Chapter 7:

Table 7. 1 . Summary of herbage accumulation results from Experi m ents

1 , 2 and 3. . . . . 1 83 Table 7.2. Results from the com bi n ed experi ment analysis for

Experiments 1 , 2, 3. . . . . 1 83

Appendix:

Table A 1 . 1 . Predicted values for feed supply and demand (Kg DM/ha/day) and average pastu re cover (Kg D M/ha) for downland areas u nder a conve ntional spri ng grazi ng manag e m e nt

situation . . . 21 4 Table A 1 .2. Predicted values for feed supply and demand ( Kg

DM/ha/day) and average pastu re cover (Kg D M/ha) for downland areas u nder a late control spri ng grazing manag e m e nt

situation . . . 21 5 Table A 1 .3. Predicted values for feed supply and deman d ( Kg

DM/ha/day) and average pastu re cover (Kg D M/ha) for the experimental site under a conventional spring g razing

management situation . . . 21 6 Table A1 . 4. Predicted values for feed supply and demand ( Kg

DM/ha/day) and average pastu re cover (Kg D M/ha) for the experimental site under a late control spri ng g razi ng

management situation . . . 2 1 7

LIST OF FIGU RES

Chapter 4 :

Figure 4. 1 . Mean ai r and soil

(

1 Ocm) tem peratures for the 1 990/9 1 and

1 99 1 /92 seasons . . . . . 50 Figure 4.2. Total monthly rainfall and pan evaporation for the 1 990/91

and 1 99 1 /92 seasons . . . .. . .

.

. . . 5 1 Figure 4 . 3 . Experi mental plots layout for t h e 1 99 1 /92 season . . . . . 52 Figure 4.4. Ryeg rass tilleri ng pattern throug hout the 1 99 1 /92 season fo r

(a) EC ; (b) LHC; and (c) LLC . . . . . . . . . 67 Figure 4.5. Botanical composition of EC (top), LHC (middle), and LLC

(bottom ) swards at pre-grazing th roughout the 1 99 1 /92 season . 82 Figure 4.6. Ratio between perennial ryeg rass (%) and clover (%) at

pre-grazing masses in Experiment 2 . . . . . . . . . 83 Figure 4.7. Relationship betwee n su mmer-autumn tilleri ng and soil

fertility as represented by (a) Olsen-P and (b) Exch-K levels

.

. . 87 Figure 4.8. Relationship between sum mer-autumn herbage

accumu lation rates and (a) spri ng and (b) su m me r-autu m n

tillering . . . . . 88

Chapter 5:

Figure 5. 1 . Predicted cu rves of (a) feed demand and supply, and (b) average pastu re cover for downland areas u nder the

conventional and the late control spring g razi ng managements

.

1 06 Figure 5.2. Predicted cu rves of (a) feed demand and supply, and (b)

average pasture cover for the e xperi mental site u nder the co n vent i o n al and the late control spri n g g razi n g

managem ents. . . . . .. . . . .. . . 1 08

Chapter 6:

Figu re 6. 1 . Mean air and soil ( 1 0cm) tem pe ratures for the 1 992/93

season . . . .. . . .. . . 1 1 4 Figure 6.2. Total monthly rai nfall and pan evaporation for the 1 992/93

season . . . .. .. . . 1 1 4 Figu re 6.3. Layout of the experi mental treatments during the 1 992/93

season . . . 1 1 9 Fig u re 6.4. Ryeg rass tilleri ng pattern for (a) E C ; (b) VFR; (c) HSR . . . . 1 30 Fig u re 6.5. Ave rage pasture cover for the three experi mental

treatments throug hout the farmlet study period . . . 1 39 Fig u re 6.6. Botanical composition of EC (top), VFR (middle), and HSR

(bottom) swards at pre-grazing throughout the 1 992/93 season . 1 45 Fig u re 6.7. Relationship betwee n the average herbage accumulation

rate (Kg D M/ha/day) and average milk solids yield (Kg/ha/day)

for the Feb ruary to April period. . . . . .. . . 1 61