Response of ryegrass and white clover to phosphorus on an allophanic soil, Egmont black loam

Abstract A phosphorus(P)‐deficient, allophanic soil, Egmont black loam, was used in a pot trial to investigate the availability of P adsorbed onto the surface of soil particles. The growth of perennial ryegrass ( Lolium perenne L.) was compared with that of white clover ( Trifolium repens L.) over a range of P additions to the soil both with and without mycorrhiza. Ryegrass and clover desorbed P from soil surfaces but clover had a higher P requirement for maximum growth than did ryegrass. Results from the trial and the adsorption curves indicated that soil solution P levels of 10 and 2 fLMP are required for near optimum growth of clover and ryegrass respectively. Clover responded to mycorrhiza at low levels of P but ryegrass showed no significant response.