Use of trimming and mineral fertilizer affects soil phosphorus availability and fractionation in a gliricidia/maize intercropping system

Abstract

Leguminous tree species are known to replenish soil nutrients through biological N fixation, mulch effect and recycling of other nutrients from the deeper soil layer to the topsoil, when managed in agroforestry systems. The soil available phosphorus (P) status and inorganic P-forms (fractionation) in a long-term gliricidia-maize trial was studied to understand the effect of additions of gliricidia prunings combined with and without inorganic fertilizers (N and P). Addition of gliricidia prunings and inorganic N and P fertilizers significantly increased phosphorus uptake by maize. Bray P1 had strong correlation with P uptake by maize in gliricidia/maize intercropping (r = 0.81, p<0.001). Both the Olsen and Bray P1 methods of extraction were strongly correlated (r = 0.80) . Phosphorus fractionation data of the soils from the maize and gliricidia-maize plots indicated that the Fe-P fraction was the most dominant form of inorganic P. The addition of gliricidia prunings significantly reduced the Fe- P and Al-P forms. We conclude that iron phosphate acts as a sink for applied inorganic P in Lixisols and the increased soil organic matter through addition of gliricidia prunings solubilizes fixed P in the soil.