Tactical versus continuous stocking in perennial ryegrass-subterranean clover pastures grazed by sheep in south-western Victoria - 1. Stocking rates and herbage production

A 4-year field experiment was carried out in south-western Victoria to dete rmine whether tactical stocking might improve perennial ryegrass (Lolium pe renne L.) persistence and prime lamb production, compared with the more com mon practice of year-around continuous stocking. Tactical stocking consiste d of variable length summer, autumn and winter rotations and continuous sto cking in spring. The 2 grazing strategies were compared on 2 contrasting pa stures: an upgraded pasture, sown with newer cultivars of perennial ryegras s and subterranean clover (Trifolium subterraneum L.) with 26 kg phosphorus /ha. year, and a more typical naturalised perennial ryegrass pasture receiv ing 6 kg phosphorus/ha. year. Paddocks were grazed by Border Leicester x Me rino ewes, which were mated to a terminal sire to lamb in September. The ef fects of the grazing systems and pasture treatments on herbage production a nd stocking rate are presented in this paper. Herbage production was simila r between the treatments, but tactical stocking significantly increased her bage mass during the growing season (P<0.05) compared with continuous stock ing. In spring each year, the herbage mass generally exceeded 3000 kg dry m atter/ha in tactically stocked paddocks and averaged 500-900 kg dry matter/ ha higher than the mass on continuously stocked paddocks. This enabled the year-round stocking rate to be increased by an average of 9% over the 4 yea rs of the experiment. We considered that the stocking rates could not be fu rther increased, despite the higher herbage mass in spring, as stock reduce d the dry herbage to a low residual mass by the opening rains in autumn. In contrast, stocking rates averaged 51% higher on the upgraded pasture compa red with the typical pasture over the 4 years of the experiment. This indic ates that pasture improvement and soil fertility status have a much greater impact on productivity than changes to grazing method. However, tactical s tocking was able to increase the sustainability of prime lamb production on upgraded pastures in a dry summer climate, by maintaining herbage cover on the paddocks over the summer-autumn period.