A comparison of annual and perennial based pastures for liveweight and wool production of sheep grazing on the lateritic podzolic soils of Kangaroo Island.

Abstract

A COMPARISON OF ANNUAL AND PERENNIAL BASED PASTURES FOR LIVEWEIGHT AND WOOL PRODUCTION OF SHEEP GRAZING ON THE LATERITIC PODZOLIC SOILS OF KANGAROO ISLAND P.R. GIBSON* Summary -, A stocking rate (Merino wethers at 10, 11, -13, 74, 15 and ) x two pasture treatments (viz: volunteer, annual grass plus subterranean clover and a renovated, perennial ryegrass plus subterranean clover) trial was run for four years on a lateritic, podzolic soil on Kangaroo Island. 17 ha Except for seven months at the beginning of the experiment sheep grazing the annual pasture weighed as much and usually more than those grazing the perennial pasture. Maximum differences in liveweight gain coincided with an 11 to 14 week interval following the opening Regressions of greasy wool production per hectare (averaged rains. over four years) on stocking rate for each treatment were linear over the range of stocking rates used and not significantly different (PC 0.05). The practice of renovating volunteer, annual pastures by sowing perennial grass species in this environment is questioned. I. INTRODUCTION Volunteer annual grass-e s plus subterranean clsov'er (Trifolium subterraneum) pastures have gen.erally yielded high le ve 1s of animal production and there is little evidence available whi Ch demonstrates that perennial based pastures will substantially increase animal production (e.g. Rossiter q952; Reed 1970). However, livestock producers have often been advised to renovate existing annual grass plus subterranean clover pastures to increase animal production, stabilize pasture composition or dilute the intake of potent, oestrogenic subterranean clovers by the grazing animal (e.g. Taylor ?961). Cutting experiments carried out at the Kangaroo Island Research Centre had shown perennial ryegrass (Lolium perenne) to be the most productive perennial pasture species inthis environment (Crawford and Smith, personal communication). This paper reports results from a grazing experiment designed to compare.wool production and liveweight response from an unrenovated, volunteer annual pasture with a renovated, perennial ryegrass based pasture. ~--~~- --~* Northfield Research Laboratories, South Australian Department of Agriculture, Box 167~ G.P.O., Adelaide, South Australia.. 325 II. MATERIALS AND METFTODS The experiment was conducted at the Kangaroo Island Research Centre, Parndana East on a lateritic podzol, The climate, soil type . and climax vegetation of the area prior to clearing have been described by Carter and Day (1970). Stocking rate (Merino wethers at AO, ?I, '3, 14, ?5 and 17 ha-' for four years) x five pasture treatments were allocated at random to land cleared from virgin scrub and sown to a subterranean clover based pasture in 1951. Reference in this paper is only made to two treatments composed of: P.. ( i1 The existing annual pasture dominated by subterranean clover cv. Yarloop and barley grass (Hordeum leporinum). Other species present wese Mt. Barker, Dwalganup and Bacchus Marsh subterra.nean myuros), soft brome (Bromus mollis), cp.peweed (Arctothecandula). (ii) A perennial ryegr?ss cv. Victorian plus subterranean clover cw. Mt. Barker and Woogenellup pasture sown into a prepared seedbed in May ?970. These two treatments are hereafter referred to as A 7n.d B respectively. Treatment A paddocks were grazed uniformly once during the winter of 1970 but treatment B paddocks remained -ungrazed until the trial was stocked with the experimental animgls in December ?970. Five, one and a half year old; merino wethers (Collinsville) were allocated to each paddock on the basis of greapy fleece ymyeight and live weight. The live weight of the sheep was recorded .Qnd fleeces dyebanded at apnroximately six weekly intervals #and individual fleeces were weighed and classed annuaJ.ly at shearing. Pasture and seed production data were also collected but not presented in this paper. III. RESULTS In three of the four years rainfall was above average resu?ting in excellent pasture growth but in 1972 a lqte break to the season, coupled with below average rainfall, delayed adequate prsture growth until the beginning of July. Treatment A pastures continued to be dominated by barley grass Treatment and Yarloop subterranean clover throughout the experiment. B pastures were dominated by perennial ryegrass in 1971 pnd 4972 but most of the perennial plants died over the 1972/T? summer resulting in an invasion by capeweed and geranium into thi,s treatment in 1973. However, self seeding of the ryegrass in ?973 rnd 1974 ensured its The subterranean clover continued contribution to pasture production. component was higher in A than B during 7971 and 1972 and the difference was greater during late autumn an; winter. Except for seven months at the beginning of the experiment sheep gra,zing the annual pasture weighed as much and usually more than those 326 grazing the perennial pasture. Maximum difference in liveweight gain coincided with an 11 to 14 week interval following the opening rains (Figure I) l 327 Regressions of greasy wool production per hectare (averaged over four years) on stocking rate for each treatment were linear over the range of stocking rates used and not significantly different (PcO.05) Treatment A outyielded B at all stocking rates in 4972 (Figure 2). but the difference between the linear regression lines only reached Only on treatment significance at the ten -percent level (Figure 2). B in 1973 at the highest stocking rate was there evidence that maximum greasy wool production per hectare may have been reached (the curve of best fit being quadratic). Additional data taken in 1973 show that sheep grazing treatment A at this high stocking rate produced 50 percent more wool than treatment B during the autumn but the difference in growth rate did not persist into the spring of that year. IV. Rapid growth of annual combined with vigorous growth waterlogged conditions in the animal productivity under the DISCUSSION grasses following the autumn break, of Yarloop subterranean clover under winter, seemed to have ensured high conditions experienced. Willoughby (1959) demonstrated the sensitivity of animal production to small increases in availability of green pasture when the latter is inadequate such as occurs in the autumn and usually the winter in this environment. Results from this study indicate that animal production from annual based pasture is at least equal to that from perennial based pasture in this enviroment and any superior performance shown by the former occurs early in the growing season. Lack of persistence by perennial species, in addition to poor performance, discourage the hope of overcoming problems related to Yarloop dominance, such as ewe infertility and clover scorch, by sowing perennial grasses on Kangaroo Island. Current studies are investigating ways of.dealing wi,th these (Beale and Crawford 1975). Additionally, there would seem no possible economic advantage to be gained from replacing annual pastures on the lateritic podzolic soils of Kangaroo Island with pastures based on perennial ryegrass. v. ACKNOWLEDGEMENTS The author wishes to thank the Australian Wool Corporation for financing the project from the Wool Research Trust Fund. Field assistance from Messrs. M.R. Lewis, P.G. Telfer, A.D. Murray and the Kangaroo Island Research Centre staff is gratefully acknowledged. VI. REFERENCES BEALE, P.E. q and&A WFORD, E.J. (1975). eicultural Record 2: 54. CARTER, E.D (1970). Australian Journal of agricultural Resezrch 2l:4' 73 READ, K.E.M (1970). Proceedings of eleventh international GrasslEds l l 0 328