effects of stocking rate and nitrogen fertilizer on a perennial ryegrass-white clover sward. 1. Sward and sheep performance

The effects of stocking rate and N fertilizer on a mixed sward of perennial ryegrass ( Lolium perenne) and white clover ( Trifolium repens ) set‐stocked with sheep were examined. Sward production and composition, and sheep production were studied. Increasing the stocking rate over the range 25–55 yearling sheep ha −1 reduced herbage accumulation by about 40%, whether or not N fertilizer was applied. Increasing the stocking rate increased the density of ryegrass tillers, but reduced the density of clover stolons and the clover content of the swards. Applications of N fertilizer (200 kg N ha −1 a −1 ) increased herbage accumulation by about 20% but substantially reduced the clover content. Liveweight gain per animal and per unit area were greater at the lower stocking rates where the clover content and nutritive value of the diet were greatest. Wool growth per unit area was greater at the higher stocking rates. Applications of 1M fertilizer increased liveweight gain at stocking rates above 25 sheep ha −1 , but had no effect on wool production at any stocking rate. The results demonstrate that a stable and productive grass‐clover association was maintained under conditions of set‐stocking at around 23 yearling sheep ha −1 and that at this stocking rate, which appears to be about the biological optimum, there was no advantage in using N fertilizer.