Phosphorus efficiency in pasture species. I. Measures based on total dry weight and P content

Two solution culture experiments were conducted to compare the efficiency of phosphorus use and indicies for measuring it in a tropical and a temperate pasture legume. The species chosen were Stylosanthes hamata cv. 'Verano' (Caribbean stylo) and Trifolium repens cv. 'Ladino' (white clover).The first experiment used two solution P concentrations (2, 16 8M) to investigate differences between species in the rate and extent of P uptake. The second experiment used five solution P concentrations (1, 2, 4, 8, 16 8M ) to evaluate differences between species in internal efficiency of P utilization.There was no difference between white clover and stylo in the capacity to remove P from the same solution P concentrations. However, in both species the extent of depletion of solutions by plants grown at high P was not as great as that plants grown at low P. The ranking of species in terms of their internal efficiency or relative growth rate changed with time and P concentrations.Growth of white clover was better than stylo where there was a moderate deficiency of phosphorus. Alternatively, growth of stylo was better than white clover where phosphorus deficiency was more severe. The relative growth rate of stylo at low (2 8M ) P was maintained above 8% per day after prolonged P stress, whilst in white clover at the same P concentration RGR fell to less than 2% per day.Internal P efficiency or the amount of dry matter accumulated per unit P accumulated per unit time showed that white clover was more P efficient than stylo in the early stages of growth.