Differential phosphorus responses of leguminous cover crops on soils with variable history

The response of 8 leguminous cover crops to phosphorus (P) application (7.5 mg P2O5 kg‐1 soil or 15 kg P2O5 ha‐1 to the depth of 15 cm) on soils with variable history was evaluated in a pot trial supplemented with a field experiment in 1993. The soil from a livestock farmer's field showed higher total organic carbon content and extractable cations compared to that from a non‐livestock farmer's field. In the pot trial, P application, on average, increased shoot, root, nodule dry matter and nitrogen (N) accumulation of the legumes by 82%, 45%, 871%, and 900%, respectively, compared to the control. Cajanus cajan, Crotalaria ochroleuca, Centrosema pascuorum, and white‐seeded Mucuna pruriens showed a higher P response than Centrosenza brasilianum and Chamaecrista rotundifolia. The legumes grown on the manured soil showed not only higher biomass and N accumulation, but also higher increase (110% and 117%) in total dry matter and N accumulation because of P application than those grown on the un‐manured soil (27% and 45%). In the field experiment, spreading legume groundcover at 16 weeks after planting was increased by 40% in the un‐manured soil and by 31% in the manured soil. Centrosema brasilimmm even showed a negative response of groundcover to P application. There was little response in erect legume height to P, except for measurements at 6 and 8 weeks after planting, when P increased plant height for Crotaktria on un‐manured soil. Results imply high returns can be expected when P is applied to leguminous cover crops in fairly fertile soil. The relatively low response under the field conditions, compared to pot, suggests caution is needed when P is recommended for legumes grown under environmentally stressed conditions.