The effects of dalapon and stocking rate on the species composition and animal productivity of a sown sward

Abstract Dalapon (2.8 kg ha ×1 ) was applied in July, either annually or biennially, to a sown sward that contained about 50% Lolium perenne measured on a ground cover basis. The sward was grazed with young beef animals at three stocking rates throughout the 4 years of the experiment. In unsprayed plots, the proportion of L. perenne declined to less than 20% (30, 14 and 16% on high, medium and low stocking rates respectively). Lolium perenne was replaced largely by Holcus lanatus and Poa spp. Annual applications of dalapon checked the decline in L. perenne . After 4 years of annual treatment with dalapon, 44% L. perenne was present on heavily stocked plots, 41% on medium stocked plots and 26% on lightly stocked plots. Biennial applications of dalapon had slightly less effect on the proportion of L. perenne . The proportion of Trifolium repens in the sward was affected by dalapon and stocking rate in much the same way as that of L. perenne . Monthly cattle weights showed that dalapon caused a slight check to individual animal performance in the month after spraying, but total liveweight gain per unit area was not significantly affected. Increasing stocking rates were inversely related to performance per animal and directly related to output per unit area. Dalapon × stocking rate interactions were generally non‐significant. There was a slight tendency for higher animal gains to be associated with higher proportions of L. perenne , but this only held for the first half of the growing season. Mean maximum liveweight gain of about 1000 kg ha −1 was achieved in 1974, by which time the proportion of Holcus lanatus had risen to a mean value of nearly 40%. The value of indigenous grasses for summer beef production is discussed.