Grass and Forage Science i\9S9) Volume 44, 11 l - l IS

RESEARCH NOTE

Yield of white clover populations in mixturewith contrasting perennial ryegrasses

ROSEMARY P. COLLINS ANDIAN RHODESAFRC Institute nf Grassland and AnimalProduction, Welsh Plant Breeding Station,Aberystwyth, UK

Abstract

A field experiment was established in May 1986 inwhich four while-clover populations originatingin Switzerland, and a bred variety, Menna, weregrown in binary mixtures with their 'co-existing"perennial ryegrasses and three other bred rye-grasses—Aurora, Talbot and Melle. The produc-tivity of both components of the mixtures wasmeasured by cutting samples in October 1986(after establishment) and on five occasions duringthe growing season in 1987, Substantial differ-ences were observed between clover yields indifferent mixtures, and the yield ranking of cloverwas found to vary with companion grass. It wasconcluded that the interaction between grass andclover populations originated at an early stage insward development, being evident in both the1986 establishment cut and the spring cut of thefollowing year. The implications of these resultsfor the formulation of breeding objectives and theevaluation of breeding material are briefly dis-cussed.

Introduction

Traditionally, white clover and grasses have beenbred separately without regard to the fact thatwhite clover is almost universally grown in mix-tures, and that aggressive grass varieties canseverely suppress clover growth (Rhodes et al..,

Correspondence: Dr Rosemary P, Collins, AFRC InsiiiuieofGrassland and Animal Produciion, Welsh PlanI BreedingStation. Plas Gogerddan. Aberysiwyih. Dyfed, SY23 3EB,

1987), Any interaction between grass and clovervarieties may contribute to the apparent unrelia-bility of forage yield in white clover. Recently, thetopic of grass/clover compatibility has receivedattention (Evans ^/fl/., 1985; Rhodes f-r a/., 1987)as the benefits of maintaining a good sward clovercontent have become evident (Frame & New-bould, 1986), In agronomic terms compatibilityin a grass/clover mixture should be refiected in thepresence of a sward clover content large enoughto optimize the benefits of nitrogen fixation andthe superior feeding value of white clover(Rhodes e; a/., 1987),

Work by Evans e( al. (1985) demonstrated thatlarge differences exist in the compatibility ofperennial ryegrass and white clover populations.Their results showed that in grass/clover mixturesbased on components which had previously co-existed (i.e. were possibly 'co-adapted') the clovermade a significantly greater contribution to totalyield than in other mixtures. In addition, largedifferences between clover yields in mixtures withtwo 'alien' perennial ryegrasses were detected. Inthese mixtures, a grass which had been bred forcharacteristics which might confer spatial com-patibility permitted better clover yield for allclover populations than did Aberystwyth S 23,suggesting that a more general compatibility canbe selected for in grasses. Improvement in grass/clover compatibility was subsequently translatedinto greater total (i.e. grass plus clover) yields(Evans et aL, 1985). The results of Evans et al.(1985) do not, however, indicate that there wasany interaction between clover and grass popula-tions in terms of clover yield, i.e. each cloverpopulation responded in a similar way to thecompanion grasses used in their experiment.

The experiment described in the present paperis a preliminary part of a comprehensive researchproject designed to examine the nature andagronomic significance of variation in compati-bility in perennial ryegrass/white clover mixtures,

MI

112 Rosemary P. Collins and Ian Rhodes

Table 1. The yield (kg ha ) cf white clover populations inbinary mixtures with perennial ryegrasses in: (a) establishment

cui (October 1986); (b) spring cul (April 1987)

Clover population

(a) Ac 3784Ac 3785Ac 3788Ac 3789Menna

Companion grass

Coexi sling

21237148

297149215

Aurora

256379221134291256

Melle

23619766

262123177

Talbol

21171

274222199195

Significance level and LSD Companion grass NSClover population NSCompanion grass x clover

population *]&2

(h) Ac 3784Ac 3785Ac 3788Ac 3789Menna

Mean

12819144

12765

111

1081239855

114100

Significance level and LSD Companion grassClover population

10314962

18185

116

NSNS

Companion grass x doverpopulalion •••76

12240

11612998

101

with the ultimate aim of defining selection criteriafor grass and clover breeding programmes.

Materials and methods

Four white clover populations collected in Swit-zerland (Chorlton & Rhodes, 1983) Ac 3784, Ac3785, Ac 3788 and Ac 3789 and a bred variety,Menna, were grown in binary mixtures with eachof four perennial ryegrasses: Aurora (very early

flowering); Talbot (intermediate flowering; usedas a companion grass for clovers in National/Recommended List trials); Melle (late flowering);and grasses ('co-existing') which had been col-lected simultaneously from the same sites as theSwiss clovers. Seed of co-existing populations wasproduced* from random samples of vegetativeplants collected from very old natural pastures.As such, these populations have distinct agrono-mic and physiological characteristics. The bredvariety, Menna, was developed from plants whichhad survived heavy inputs of N fertilizer in apasture in Surrey, UK; its co-existing grass wasthe variety Ajax, developed from plants collectedfrom the same location (Evans et al., 1985).

The experiment was sown in May 1986 as acomplete randomized-block design incorporatingfour replications. The plots (2-25 m') were sownwith the appropriate mixture at a rate of 2-5 and13 kg ha"' ofciover and grass, respectively. Basalfertilizer was applied to the plots in the form of 51ha~' ground limestone, and 0-251 ha "' muriate ofpotash and superphosphate. No additional nitro-gen was supplied to the grass/clover mixtures.Plots were cut at intervals after establishment toencourage an even distribution of clover in themixtures.

The flrst sample was harvested in October1986. Five harvests were made in 1987; 22 April,10 June, 6 July, 18 August and 28 September.Harvesting was carried out by removing a 025 m^sample cut to a height of 5 cm from the centre ofeach plot usiiig electric shears. After sampling,the entire experimental area was cut to 5 cm usinga mower. The material in the samples was sub-sampled, then separated into its clover and grassconstituents, dried and weighed.

Tabk 2. Annual dry matter yield (kg ha ) of white clover populations in binary mixtureswith perennial ryegrasses in 1987

Clover population

Ac 3784Ac 3785Ac 3788Ac 3789Menna

MeanSignificance level and LSD

1

Coexisting

432261544861673652445467

"ompanion grass

1 Aurora

622957425330535559615723

Companion grassClover population

Melle

557952484733614151745375NS

•688

Talbot

563540765304633348975249

Companion grass x clover population

Clover populationMean

544153055062614153195454

*I377

Clover yields with contrasting ryegrass 113

20001

1000

1000'

? 1000

1000

2000

1000

Ac 3789

Ac 3788

Ac 37S5

Ac 3784

MENNA

Apr. May Jun Jul Aug Sep

MonthFigure I.Theyieldofwhilecicverpopuiationsinbinary mixtures wilh perennial ryegrass during 1987growing season: coexisting grass (• ), Aurora (- -), Melle (•• ) and Tatbot (—).

Results

The yields ofciover populations in October 1986(establishment cut) are shown in Table I (a). Inthis harvest there was a significant interactionbetween companion grass and clover population.The clover populations Ac 3785 and Ac 3788, inparticular, showed large differences in yielddepending on the companion grass. Ac 3785produced a significantly higher yield with its co-existing grass and with Aurora than it did witheither Melle or Talbot. Conversely, Ac 3788 was

more productive with Talbot and Aurora thanwith its coexisting grass or with Melle.

Table 1 (b) shows the yields obtained in the firstharvest in 1987 (spring cut). There were apparentsimilarities between this harvest and that of theprevious October. A significant grass x cloverinteraction was observed; the yields of Ac 3785,3788 and 3789 varied significantly with compa-nion grass. As in the previous harvest, Ac 3785produced a high yield with its co-existing grassand its lowest yield with Talbot. In contrast, Ac3788 performed worst with its coexisting grass

114 Rosemary P. Collins and Ian Rhodes

and best with Talbot. Ac 3789 produced itshighest and lowest spring yields with Melle andAurora, respectively.

Annual dry-matter yields of the clover compo-nent of each mixture are presented in Table 2.Again, there was a significant grass x clover inter-action, with the ranking order of the yields of Ac3784, 3785 and 3789 changing according to thecompanion grass. When the lowest and highestannual clover yields were compared for a givenclover population, the greatest yield enhancementwas found in Ac 3785 with its co-existing grass(51 % greater than its yield with Talbot). The yieldof Ac 3784 was 44% greater with Aurora thanwith its coexisting grass; conversely, Ac 3789produced 26% more with its co-existing grassthan with Aurora. The yield of Ac 3788 wasparticularly consistent across companion grasseswith only a 13% difference between its highest(Aurora) and lowest (Melle) mixtures.

Figure I shows the seasonal distribution ofclover fields in mixture with each grass during thefirst full harvest year (1987). A least significantdifference value is included for harvests one andtwo, where a significant grass x clover interactionoccurred. Differences in yield between cloverpopulations were evident in the first three har-vests, but diminished thereafter.

Discussion

It is clear from the results presented that largedifferences exist in the performance of cloverpopulations grown in mixture with difFerent grasspopulations. In particular, with respect to estab-lishment, spring and annual dry-matter yield theranking order ofciover populations was observedto change according to the companion grass.Such interactions have not previously been de-scribed in the literature. The substantial differ-ences found in clover yield at the end of the firstharvest year are likely to be refiected in totalyields in the next harvest year, although notnecessarily in subsequent years, because theinfluence of nitrogen transfer from the cloverbecomes an important influence on the producti-vity of the mixture (Evans e! ai, 1985).

It is of interest to note that the grass x cloverinteraction was evident even in the first harvestcarried out in this experiment (October 1986).Some broad similarities between clover yields inthis harvest and annual yield in 1987 can bedistinguished, which suggests that differences in

clover pierformance originated at an early stage inthedevelopment of the sward. It appears from theseasonal pattern ofciover production (Figure 1)that differences between populations were greaterin harvests one to three, so that differences inannual yield are determined by growth in springand early summer.

The physiological mechanisms underlying dif-ferences in grass/ciover compatibility are as yetunclear, but are thought to operate throughvariation in the spatial arrangement of plant parts(spatial compatibility), and through variation inseasonal growth patterns (Rhodes, 1981; Evans ela!., 1985). Spatial compatibility is likely to beinfluenced by above- and below-ground factorssuch as root and shoot arrangement, morphologyand physiology (Rhodes ef al., 1988). Preliminarystudies (Collins, R.P., unpublished data) haveemphasised the importance of root competitionin the suppression of Ac 3785 with Talbot duringestablishment. Temporal compatibility involvesthe interaction of variables such as the springgrowth potential and cold hardiness of the clover,and the seasonal growth pattern and floweringdate of the grass (Rhodes et al., 1988). The resultsof this experiment show, for example, that mix-tures which include Aurora arc often more pro-ductive in terms of clover yield than othermixtures. Aurora is an early flowering variety,and it has been shown that the competitive abilityof grasses declines with the onset of fiowering(Rhodes, 1970). This characteristic of Auroramay afford the clover component a greater com-petitive advantage earlier in the growing seasonthan those of later flowering grass varieties. Therewere, however, exceptions to this trend in thepresent experiment, e.g. the performance of Ac3789 with Aurora in harvests one and two in 1987.The poor growth of Ac 3785 with Talbot in thefirst three harvests in 1987 is difiScult to explainsince other clover populations yielded relativelywell with this grass. More detailed physiologicalknowledge is required to explain these results.

The finding that not all clovers performed wellwith their coexisting grass contrasts with theconclusions of Evans et al. (1985). As yet, noexplanation can be proposed for this difference.However, it is worth noting that in the latter studythe observed co-adaptation may have resultedfrom grass and clover adaptation to major en-vironmental factors; the plant collections havingbeen made from a wide range of environments. Inthe present study collections were made from

Clover yields with contrasting ryegrass 115

within a more restricted range of environments inwhich cold winters are the predominant feature.Although the coexiting populations were col-lected from the same fields the frequency ofoccurrence and, therefore, the chance of plant-to-piant co-adaptation may differ markedly betweensites. In addition, plant collections were made ona single day and it is therefore impossible to relatethe abundance of the species at that time to thecompatibility effects described in this paper.

It should be emphasised that the yields in thisexperiment were obtained under a cutting regime.In such a system clover rapidly becomes domi-nant, with a concomitant reduction in grasscontent. Trends identified in this work may beaccentuated or modified under grazing whenclover proportions are much lower, because ofremoval ofciover stolon by the animal.

The interactions between grass and cloverpopulations described here have important impli-cations for the evaluation of clover varieties byofi!icial bodies for National and RecommendedLists, Currently in the UK, only Talbot is used asa companion grass and clover yield in mixture isthe primary criterion for determining the successof a variety. In future it may be necessary to useseveral companion grasses, or, alternatively testspecific grass/clover mixtures against severalstandard mixtures. In this case both clover andmixture yields would be used as criteria forcompatibility. Before such modifications in test-ing are made, more information is required on thelong term effects of grass and clover variety

interactions, particularly under realistic grazingconditions. The large differences in clover yield,which are obtained by mixing compatible grassesand clovers emphasise the importance of breedingfor compatibility in clover and grass breedingprogrammes (Rhodes et al., 1987). For such aprogramme to be developed it is essential that thephysiological mechanisms underlying the interac-tions are understood, and the characters contri-buting to compatibility are identified for use asselection criteria.

References

CHORLTON K,H, and RHODES 1.(1983) Extending and maintain-ing genetic resources—collecting Loiium. Fe.uma and Tri-foliurn in Switzerland, Annual Repori of tbe Welsh PloniBreeding Staiinn. 1982. pp, 33-34,

EVANS D,R, , HILL. J,. WILLIAMS T,A, and RHODES I, (1985)Effects of coexislence on Ihe performance of while clover-perennial ryegrass mixiures, Oecologiu. 66, 536-539.

FRAME J, and NEWBOULD P. (1986) Agronomy of white clover.Advances in Agronomy, 40, 1-88,

RHODES I. (1970) Competilion in herbage grasses. HerbageAb.uract.-i, 4a, 115-119,

RHODES 1, (1981) The physiological basis of variation in theyield of grass/clover mixtures. In: Wrighi, C,E, (ed,). Plantphysiology and herbage production. Britisb Grassland SocietyOccasional Symposium No. 13. pp, 149-161,

RHODES 1,, COLLINS R,P , . GLnsDr-JiNO M,J, and EVANS D , R .(1988) Breedmg while clover in relation lo biolic and climaticfaciors. In: Poisson, C, (ed,), Naiuru! viirintwn and breedingfor (idapUiiion. Proceedings ol Eucarpia Fodder Crop^ SectionMeeting Lu^ignan. 119-124 pp.

RHODES I.. GLENDININC M,J, and COLLINS R,P, (i987)The basisof compaiibiliiy in while clover/ryegrass mixtures. In: Gela-bert. L, M-G (Ed,), Proceeding.^ of EEC Work.^hop on Pa.\iureImprovemeni. pp, 15-20, Luxembourg: Commission of theEuropean Communities,

{Received 18 March 1988, revised 15 July 1988)