The response to phosphate of two annual pasture species. I. Effect of the soil’s ability to adsorb phosphate on comparative phosphate requirement

Eleven soils which differed widely in their ability to adsorb phosphate were used in a pot trial to compare the response to phosphate by subterranean clover (Trifolium subterraneum L.) with that by Wimmera ryegrass (Lolium rigidum Gaud.). Response curves were fitted to the yields (log-transformed). The coefficients of the curves were used to calculate both the relative effectiveness of the phosphate and the phosphate required to give a given fraction of the increase in log yield due to phosphate. Overall, the phosphate requirement for the grass was less than for the clover but the two species were affected differently by the soil’s ability to adsorb phosphate. The phosphate requirement for the clover increased more rapidly with increasing adsorption by the soil than the phosphate requirement for the grass.