Competition between grass and clover for phosphate

Fifteen rates of superphosphate (0–897 kg/ha) were applied to white clover grown alone or with browntop on soil deficient in Nand P. Plots were mown and all herbage removed. Browntop reduced clover dry matter and N yields, especially when swards were younger or when fertiliser N was applied when swards were older. Competition for P was important when the supply of P was suboptimal and when swards were younger, but with time, other factors, which probably included shading of clover stolons by the browntop mat, became more important. Increases in superphosphate, often substantial, only partially overcame the reduction in yield. These competitive factors affected clover herbage N yields but did not alter increases in soil N. It is suggested that competition will be stronger under grazing than under mowing, and it limits the realisation of the N‐fixing potential of white clover.