Effect of legume incorporation on solubilization of Ogun phosphate rock on slightly acidic soils in SW Nigeria

Most soils in Nigeria are known to be slightly acidic and very low in plant-available P. These soils need to be fertilized for optimal crop production but cost and scarcity of mineral P fertilizers shifted attention to making direct application of indigenous phosphate rock viable alternative. Laboratory and greenhouse studies were carried out to monitor the effect of the decomposition of legume biomass on the solubilization of Ogun phosphate rock (OPR) on slightly acidic soils. Surface soil samples collected from three experimental sites in SW Nigeria were used. The fertilizer treatments were four rates of P as OPR (0, 30, 60, and 90?kg ha1) and one rate of triple superphosphate (TSP, 40?kg P ha1). The legume treatments were cowpea (Vigna unguiculata L Walp) and mucuna (Mucuna puriens L). Rice (Oryza sativa) was used in the greenhouse study as the test crop. Soil samples were analyzed for soluble P and pH after 2, 4, 6, and 10 months of incubation in the laboratory while plant tissues collected from greenhouse study were analyzed for P. In the incubation study, significant increase in water-soluble P was observed when legume biomass was incorporated with phosphate rock at p < 0.05. Highest value in rice dry-matter yield was recorded with pots treated with mucuna and TSP, also treatment combination of cowpea and OPR significantly increased rice dry-matter yield by 16% over pots treated with cowpea biomass alone and 42% over control pot (no legume biomass and OPR in the green house (p < 0.05). Thus incorporation of legume biomass significantly increased rate of OPR solubilization.