Initial and residual responses of Verano Stylo [Stylosanthes hamata (L.)] and Centro [Centrosema pascuorum (Benth.)] to phosphorus in ungrazed swards

Abstract

A field study was carried out to investigate the responses of Stylosanthes hamata and Centrosema pascuorum. (Benth.) to the initial and residual effects of phosphorus (P) application in 1989 and 1990 at Kurmin Biri and Kontagora in the guinea savanna zone of Nigeria. Five levels of P: 0, 20, 40, 60, and 80 kg ha^-1, were applied to each legume. The experiment was carried out over two years, without further P additions, to determine P's residual effects on the test crops. The responses to applied P depended on forage species and location. The P increased dry matter (DM) yield significantly in both legumes and years except C. pascuorum in which P application did not substantially influence the DM in the second year of establishment. Apart from the C. pascuorum grown at Kontagora (second year), yield increases over the first-year trials were observed in the levels of DM produced in the second year. The application of P significantly improved seed production from forages. Judging from the low P values of 4.50 mg kg^-1 and 5.35 mg kg^-1 of the soils, very high response to applied P was expected. The applied P at 80 kg ha^-1 to C. pascuorum at Kumin Biri gave the highest seed yield (1564.00 kg ha^-1) while unfertilized S. hamata at Katongora had the least (403.00 kg ha^-1). The relatively low but significant response of forage species to P was attributed to the high level of P fixation and the abundance of inactive P forms in these soils.