Effects of different phosphorus-efficient legumes and soil texture on fractionated rhizosphere soil phosphorus of strongly weathered soils.

Phosphorus (P) deficiency is one of the largest constraints to crop production in tropical Africa; so, it is necessary to better exploit soil P resources through increasing labile soil P using P-efficient plants. The aim of this study was to evaluate the effect of various P-efficient legumes on fractionated rhizosphere soil P in two contrasting textured soils of Tanzania, i.e., strongly weathered soils. We conducted a 30-day pot experiment, where white lupin ( Lupinus albus L.; WL), cowpea ( Vignaungui culate L.; CP), and pigeon pea ( Cajanus cajan L.: PP) were grown with and without N application (0 and 50 kg N ha). Plant growth, P uptake, rhizosphere pH, and fractionated soil P were investigated. Plant P uptake decreased in the following order: WL > CP > PP in clayey soil and CP > PP > WL in sandy soil. We observed clear effects of all legumes on the rhizosphere soil P dynamics of all fractions in both soils, except for the labile P fraction in clayey soil. The effect of legume growth on the contents of less labile inorganic P fraction (NaOH-P) was significantly different between legumes; NaOH-P contents of WL was significantly lower than those of CP and PP. All legumes substantially increased the less labile organic P fraction, and its ratio was significantly higher in sandy soil. Our results suggest that WL had different P mobilization characteristics from CP and PP and that the effect of P-efficient legume cultivation on soil P availability should be more important in the inherently P poor sandy soil than in clayey soil. [ABSTRACT FROM AUTHOR]