An evaluation of three aerial pasture development methods on the Northern Tablelands of New South Wales, in terms of herbage on offer, botanical composition and animal performance

Abstract

Herbage mass on offer, botanical composition and livestock production of sheep grazing 3 types of pastures developed by 'aerial' methods at 3 stocking rates (5, 7.5 and 10 sheep/ha) were compared in a 3-year grazing trial at Glen Innes, N.S.W., during 1972-75. The pastures were: resident grass-white clover (F), resident pasture plus surface sown grass (SF), and as for SF but with herbicide application prior to surface sowing ofgrass (HSF). All pasture treatments had equivalent rates of superphosphate applied. The sowing effect and the herbicide effect were statistically analysed by contrasting the pasture treatments: SF-F, HSF-SF, respectively. The SF-F contrast showed that herbage on offer of the sown grasses on the SF pasture was greater, and this difference increased with time. Legume herbage on offer was greater on the SF pasture though it declined with time, and exhibited seasonal variation. The HSF-SF contrast indicated that herbage on offer: of sown grass was greater on the HSF pasture and increased with time; of the herbs component was greater on the HSF pasture during the initial and final stages of the experiment; oflegume was greater on the HSF pasture but the difference declined with time; of resident grass was greater on the SF pasture but the difference declined with time; and of dead material was consistently greater on the SF pasture. The contrasts for the resident grasses and dead material components varied seasonally. Herbage on offer of all pasture components declined as stocking rate was increased. Patterns of decline varied with pasture component and pasture treatment. Mean sheep liveweights were influenced by pasture treatment, with sheep on the HSF pasture being the heaviest, and those on the F pasture, the lightest. Increasing stocking rate decreased mean sheep liveweights on pastures F and SF but increased mean sheep liveweights on the HSF pasture. Liveweight declines were least for sheep grazing the F and SF pastures and liveweight increases were greatest on the HSF pasture during late summer-autumn. Greasy wool production per sheep was greatest on the HSF pasture during 1972-73 but thereafter there were no significant differences between treatments. We conclude that, although animal production was increased by the introduction of sown grasses in the short term, the level of superiority was not as great as expected. Changes in management strategies may be required if the greater production achieved is to be sustained.