The responses of hexaploid caucasian clover
(Trifolium ambiguum) to four contrasting grazing
regimes were compared with those of white clover
(T. repens) in an endophytic (Neotyphodium lolii)
hybrid ryegrass pasture on a fertile lowland site.
After 2 years, frequent grazing (set stocking) by
sheep reduced caucasian clover cover to 10%
compared with 25.5% in infrequent grazing
(rotational grazing) treatments (mean spelling time
25 days). Similarly, frequent grazing reduced
caucasian clover rhizome plus root dry weight (780
kg DM/ha when sampled to 100 mm depth in
frequently grazed plots, compared with 3220 kg
DM/ha for infrequent). Under frequent grazing
treatments, mean white clover cover was 21%,
under infrequent hard grazing it was 26% and under
lax infrequent grazing it was 14%. The reduction
in ryegrass tiller population from 5720/m² in the
infrequently and laxly grazed treatments to 4150/
m² in the frequently hard grazed pastures indicated
the severity of that hard grazed treatment. These
results show that in lowland ryegrass pastures on
high fertility sites, the stoloniferous growth form
of white clover may be superior to the rhizomatous
strategy of caucasian clover when grazing by sheep
is frequent throughout spring, summer and autumn

Jarvis, Peter

Lucas, Richard J.

Moorhead, A. J. E.

Nichol, Wayne W.

Sedcole, John R.

Lincoln University Research Archive

203Proceedings of  the New Zealand Grassland Association 60: 203–206 (1998)Frequent grazing by sheep reduced caucasian clover cover and rhizome massin ryegrass pastureR.J. LUCAS, A.J.E. MOORHEAD, W.W. NICHOL, J.R. SEDCOLE and P. JARVISDivision of Soil, Plant and Ecological Sciences, PO Box 84,Lincoln University, Canterbury, New ZealandAbstractThe responses of hexaploid caucasian clover(Trifolium ambiguum) to four contrasting grazingregimes were compared with those of white clover(T. repens) in an endophytic (Neotyphodium lolii)hybrid ryegrass pasture on a fertile lowland site.After 2 years, frequent grazing (set stocking) bysheep reduced caucasian clover cover to 10%compared with 25.5% in infrequent grazing(rotational grazing) treatments (mean spelling time25 days). Similarly, frequent grazing reducedcaucasian clover rhizome plus root dry weight (780kg DM/ha when sampled to 100 mm depth infrequently grazed plots, compared with 3220 kgDM/ha for infrequent). Under frequent grazingtreatments, mean white clover cover was 21%,under infrequent hard grazing it was 26% and underlax infrequent grazing it was 14%. The reductionin ryegrass tiller population from 5720/m2 in theinfrequently and laxly grazed treatments to 4150/m2 in the frequently hard grazed pastures indicatedthe severity of that hard grazed treatment. Theseresults show that in lowland ryegrass pastures onhigh fertility sites, the stoloniferous growth formof white clover may be superior to the rhizomatousstrategy of caucasian clover when grazing by sheepis frequent throughout spring, summer and autumn.Keywords: caucasian clover, cover, grazing fre-quency, grazing intensity, kura clover, rhizomes,ryegrass, Trifolium ambiguum, Trifolium repens,white cloverIntroductionCaucasian clover is recognised in New Zealand andAustralia for its potential as a persistent legume inrangeland (Allan & Keoghan 1994; Virgona & Dear1996). Seed of hexaploid caucasian clover cultivars isnow available and sowings are being promoted beyondthe well-demonstrated rangeland niche. Information istherefore required on the agronomy of caucasian cloverfor lowland pastures and its grazing requirements underhigh stocking rates in intensively managed pastoralsystems.Few experiments on caucasian clover defoliationfrom fertile lowland sites have been reported: Stewart& Daly (1980) showed monthly cutting produced about20% less tetraploid caucasian clover than bi-monthlycuts; Sheaffer et al. (1992) in Minnesota showedhexaploid caucasian clover was an aggressive competitoragainst Lotus corniculatus under lenient rotationalgrazing by sheep; Petersen et al. (1994a), also inMinnesota, showed a 30% reduction in yield with sixcuts per growing season compared with three cuts inpure caucasian clover stands in the third year of theirstudy after little difference in the first 2 years. They alsoshowed that sheep grazing with 14- and 28-day spellingperiods resulted in successive decreases in total forageproduction over a 3-year period. Nevertheless, theyconcluded that caucasian clover tolerates frequent andclose defoliation.None of those experiments challenged caucasianclover with frequent intensive grazing in the presenceof an aggressive pasture grass or a grazing tolerantlegume. An experiment with four contrasting grazingtreatments was therefore initiated in 1992 to comparecaucasian clover with white clover in a dense ryegrasssward of high endophyte status on a fertile soil.Materials and methodsThis grazing experiment is located on a flat site (11 ma.s.l.) at Lincoln University (43° 39’S, 172° 28’E). TheTempleton sandy silt loam has variable depth (600–1500 mm) over gravel, pH 5.4 and Olsen P 16.Rainfall was supplemented with irrigation to ensurepasture production did not cease during dry summers.The site received a total of approximately 900 mm rainplus irrigation in both years (1993/94 and 1994/95).Mean soil temperatures at 100 mm depth ranged between17°C in February and 2°C in July.Hexaploid caucasian clover (Trifolium ambiguumcv. Monaro) and three other lines of rhizomatous cloverswere sown on 22 March 1989 in rows, 0.75 m apart, at100 viable seeds/m row for a seed production investi-gation. There were four rows per plot with 0.75 mbetween plots. The plots were 80 m long and 3 m wideto allow for proposed mechanical seed harvesting. Thefour legume treatments were replicated three times togive an experimental area of about 80 × 52 m. This204earlier study ceased after 3 years because of the vigourof adventive white clover (T. repens) from seed reservesin the soil.Hybrid ryegrass (Lolium × boucheanum syn. L.hybridum cv Marsden) with a high level of loliumendophyte (Neotyphodium lolii) was drilled at 15 kgseed/ha into the clover turf in spring 1992. Aftersuccessful grass establishment the area was rotationallygrazed by sheep until August 1993. In early spring1993, the area was fenced across the rhizomatous cloverplots to give eight plots of 52 × 10 m. Each of thesegrazing treatment main plots contained 12 rhizomatousclover sub-plots (10 × 3 m) with strips of adventivewhite clover between each sub-plot.Four grazing treatments were applied in spring,summer and autumn of 1993/94 and 1994/95. All plotswere grazed to a low pasture mass of 700 kg DM/haeach winter.The two factors in the experimental design weregrazing frequency (set stocking vs rotational grazingwhich had 4-day grazing durations and about 25-dayspells) and grazing intensity (hard and lax). Pastureswere managed to achieve pasture masses of between600 and 1000 kg DM/ha for hard set stock and 1500–2500 kg DM/ha for lax set stock. Rotationally grazedtreatments had pre- and post-grazing pasture masses ofabout 2000 and 600 kg DM/ha for rotational hard and3000 and 1800 kg DM/ha for rotational lax. Becausethe plots were limited in area (520 m2), set stockingwith a minimum flock size of three ewe hoggets wasachieved during periods of low pasture production byrotationally grazing the hard set stock plots for durationsof 4 or 5 days and then the lax set stock plots for 2 or 3days. The set stocked plots therefore had spelling timesof 2–5 days during low pasture production periods.This paper reports results of caucasian clover andwhite clover sub-plots only.Cover was determined by placing the point analyserat right angles across the clover rows in the replicates ofthe caucasian clover sub-plots within each of the grazedplots. White clover was sampled from pasture areasimmediately adjacent to the caucasian clover sub-plots.Underground biomass was sampled by taking eight cores(50 mm diameter × 100 mm deep) per sub-plot withinthe original drill rows in August 1995.ResultsDuring the first year of grazing caucasian clover hadsimilar cover to white clover in set stocked treatmentsand was superior to white clover in the rotationallygrazed treatments (Table 1). Cover changed during thesecond year and by the end of the second year, caucasianclover cover was about half that of the white clover inset stocked treatments with hard set stock being mostseverely affected. In contrast caucasian clover coverwas greater than white clover under lax rotational grazingwhile both clovers had similar cover values under hardrotational grazing.After 2 years the underground caucasian cloverbiomass values were proportional to leaf cover. Underhard set stocking, root plus rhizome biomass was mostdepleted, while hard rotational grazing had over seventimes the underground biomass. More roots of ryegrass(3.0 t DM/ha to 100 mm depth) were extracted from soilcores sampled from laxly grazed plots compared with2.3 t in hard grazed plots, but the difference was notsignificant (P = 0.2).The sward characteristics in October 1995, 2 yearsafter grazing treatments started, showed the severity ofthe hard set stock treatment as indicated by reducedryegrass tiller numbers and the invasion of weeds intothe “overgrazed” pasture (Table 1). In the previousautumn there was significantly more bare ground in setstocked plots and both lax grazed treatments had a highproportion of dead leaf and reproductive stem.DiscussionContrary to expectation, the present results showed thatcaucasian clover cover was adversly affected by setstocking compared with white clover. The reduction incaucasian clover cover was correlated with a reductionin underground biomass under set stocking. Both cloverswere productive under hard rotational grazing butcaucasian was more tolerant of the high pasture mass inthe lax rotationally grazed plots.------------- Grazing treatment -------------Pasture component Set stock Rotational grazingHard Lax Hard Lax SEDMean grazing pressure 480 330 700 350(grazing days/ha)First grazing yearCover Caucasian 14 14 21 17 1.7(%) White 16 11 7 5 2.3Grass 53 62 59 68 2.8Others 17 13 13 10 -October 1995, after 2 years grazingCover Caucasian 7 13 28 23 2.2(%) White 18 24 26 14 2.8Weed 24 4 8 6 -Underground biomass(t/ha) Caucasian 0.5 1.1 3.7 2.7 0.50Ryegrass 2.5 3.3 2.2 2.8 0.62Tillers(no./m2) Ryegrass 4150 5750 5700 5710 780Table 1 Changes in caucasian and white clover based endophyticryegrass pastures under four contrasting grazing regimesover two years.205Other grazing studies have indicated that caucasianclover may be sensitive to frequent defoliation but nonehave used such severe treatments nor have they shownsuch large differences between treatments. Ourexperiment challenged caucasian clover plants withcompetition from endophyte infected ryegrass, whiteclover and selective grazing by sheep from Septemberto May over 2 years.The greatest underground biomass sampled to adepth of 100 mm after 2 years of the grazing treatmentsin the 6-year-old Monaro caucasian plants was 3.7 tDM/ha in the hard rotational treatment and only 0.5 tin the hard set stock treatment. These values are muchless than the 20 t DM/ha to a depth of 200 mmunderground biomass from a 14-year-old, ungrazed,well fertilised, Canterbury high country site reportedby Strachan et al. in 1994. Peterson et al. (1994b)reported a 20% mean decrease from 7.5 t to 6 t DM/hain below ground biomass (sampled to 150 mm) duringthe second year of their cutting experiment but thethree, four, five and six cuts/season had little effect.Peterson et al. (1994b) claimed that their frequentgrazing of a caucasian clover monoculture had littleeffect on below ground biomass, but they did in facthave greater underground biomass in their 28-dayspelling treatment than in their 14-day treatment. In an11-year-old site at Lincoln University adjacent to thegrazing trial described in this paper, we measured 7.5 tDM/ha to 150 mm of underground biomass in December1997 from Monaro caucasian clover plots (Lucasunpublished); these plots were initially used for seedproduction studies (Daly et al. 1993) but had beeninvaded by annual grasses and grazed four or five timesper year for 6 years before sampling.These reports suggest that although caucasian clovermay develop a very large underground biomass of rootsand rhizomes when ungrazed, grazing and competitionfrom other plant species deplete its undergroundreserves. The response to frequent defoliation incaucasian clover has similarities to tap-root depletionand decreased herbage production observed in lucerne,red clover and chicory.The results from our grazing experiment were notexpected because rhizomes were perceived to be theultimate grazing avoidance strategy for very palatablepasture species (Forde et al. 1989). Also, the depletionof caucasian clover rhizomes and roots under a frequentsevere grazing regime was perplexing, as there are largeareas in eastern Turkey where caucasian clover maintainsa strong presence in spite of having been grazed formillennia (A.H. Nordmeyer pers. comm.).The depletion of rhizomes and roots under severefrequent grazing (hard set stock) for the full growingseason from spring to early winter suggests thatpersistence of caucasian clover may be compromisedunder this extreme management. Further work is requiredon the productivity and persistence of caucasian cloverunder less extreme, more typical grazing management.For instance, New Zealand sheep farmers usually setstock ewes and lambs in spring but rotationally grazefor the rest of the year. This sheep farming grazingregime, which includes summer and autumn rotationalgrazing, should suit the apparent need for caucasianclover to be spelled so it can recover and/or maintain itsunderground biomass.ConclusionsCaucasian clover may be better adapted to rotationalgrazing than white clover, but set stocking will reduceits cover and underground biomass, the amount ofreduction depending on grazing intensity.REFERENCESAllan, B.E.; Keoghan, J.M. 1994. More persistentlegumes and grasses for oversown tussock country.Proceedings of the New Zealand Grassland Associ-ation 56: 143–147.Daly, G.T.; Gurung, J.; Lucas, R.J. 1993. Stand age andclosing date effects on seed yield of caucasian cloverand zigzag clover cultivars. Proceedings of the XVIIInternational Grassland Congress: 1664–1666.Forde, M.B.; Hay, M.J.M.; Brock, J.L. 1989. Devel-opment and growth characteristics of temperateperennial legumes. pp. 91–109. In: G.C. Marten etal. Persistence of forage legumes. Proc. Australian/New Zealand/United States Workshop, Honolulu,July 1988. ASA, CSSA and SSSA, Madison, WI.Peterson, P.R.; Sheaffer, C.C.; Jordan, R.M.; Christians,C.J. 1994a. Responses of kura clover to sheepgrazing and clipping: 1. Yield and forage quality.Agronomy journal 86: 655–660.Peterson, P.R.; Sheaffer, C.C.; Jordan, R.M.; Christians,C.J. 1994b. Responses of kura clover to sheepgrazing and clipping: 2. Below-ground morphology,persistence and total nonstructural carbohydrates.Agronomy journal 86: 660–667.Sheaffer, C.C.; Marten, G.C.; Jordan, R.M.; Ristau,E.A. 1992. Forage potential of kura clover andbirdsfoot trefoil when grazed by sheep. Agronomyjournal 84: 176–180.Stewart, A.V.; Daly, G.T. 1980. Growth of an establishedstand of Trifolium ambiguum in a fertile lowlandenvironment. New Zealand journal of experimentalagriculture 8: 255–257.Strachan, D.E.; Nordmeyer, A.H.; White, J.G.H. 1994.Nutrient storage in roots and rhizomes of hexaploid206caucasian clover. Proceedings of the New ZealandGrassland Association 56: 97–99.Virgona, J.M.; Dear, B.S. 1996. Comparative per-formance of caucasian clover (Trifolium ambiguumcv. Monaro) after 11 years under low-input con-ditions in south-eastern Australia. New Zealandjournal of agricultural research 39: 245–253.!

Frequent grazing by sheep reduced caucasian clover cover and rhizome mass in ryegrass pasture

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