Phosphorus availability to soyabean from an indigenous phosphate rock sample in soils from southwest Nigeria

Laboratory and grecnhouse experiments were conducted on 12 soil samplesin Ogun State of Nigeria to evaluate the comparative transformation of Ogunphosphate rock (OPR), single Superphosphate (SSP) and OPR: SSP mixture withinsoils, and to determine the response of soyabean to the direct application ofthese sources. The OPR sample was found to contain 0.3% P soluble in water(2.7%of total P) and 3.4% P soluble in 2% formic acid (28.5% of total). Changes inthe values of the P fractions in soils were affected significantly by soiltype,P source and rate of application. The percent increase in Olsen P from OPRafter12 weeks of incubation averaged 44.5, 39.6 and 36.7% in Entisols, Alfisols andUltisols, respectively. All the soils responded to OPR, OPR: SSP and SSPapplication. Responses to OPR were found to be related inversely to soil pH (r=0.82). At the application rate of 60kg Pha−1, the relative agronomic effectiveness of OPRand OPR: SSP varied from 11.6 to 92.3% (mean 61.3%) and 11.6 to 101.1% (mean51.4%), respectively. It was concluded that direct application of OPR as Psource for soyabean in soils from southwest Nigeria is feasible.