Phosphate uptake from extended soil solutions by pasture plants

A solution culture (in which an extended soil solution, separated from, but in equilibrium with, the soil) was used for growing pasture plants under controlled conditions of constant P in the range 0.2‐5μMol P /litre. Plant responses to P over the whole growth period, as indicated by Michaelis‐Menten Km values, were compared with those obtained from integrated progress curves of the time course of P uptake by plants from solutions undergoing P depletion. Browntop ( Agrostis tenuis ) achieved almost maximum growth at 3 μM P, but white clover ( Trifolium repens ) appeared to need P concentrations greater than 5 μM. This difference could account for much of the competitive superiority of browntop over white clover when they are grown in association under low P supply.