Analysis of the response of pasture legumes to phosphorus in a controlled environment

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Abstract
White clover [Trifolium repens], red clover [T. pratense], suckling clover [T. dubium] and lotus [Lotus pedunculatus] were grown under a controlled environment in soil to which P had been added at levels of 50, 250, 600 and 2000 ppm wt/wt. Growth analysis was used to explain differences in yield in terms of attributes describing growth, P uptake and assimilation. The yield of white clover, red clover and lotus increased markedly with P supply. Suckling clover responded less to P and its yields were smaller than those of the other species except that of lotus at 50 ppm. In all species the rate of P uptake per unit root length increased with P supply. There were differences in uptake rate among species, but these could not be consistently related to differences in yield. The efficiency with which absorbed P was used in the production of dry matter declined as the P supply increased in all species. Lotus used P with the greatest efficiency. Root/shoot ratios and root length/weight ratios were affected by an increase in P supply. Suckling clover had the highest root/shoot ratios and lotus had the lowest. Suckling clover also had high root lenght/weight ratios. For these legumes, attributes such as root/shoot ratio, root length/weight ratio, P concentration and inherent size appear to be more useful than P uptake in explaining response to P.