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

Laboratory and greenhouse experiments were conducted on 12 soil samples in Ogun State of Nigeria to evaluate the comparative transformation of Ogun phosphate rock (OPR), single Superphosphate (SSP) and OPR: SSP mixture within soils, and to determine the response of soyabean to the direct application of these 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 in the values of the P fractions in soils were affected significantly by soil type, P source and rate of application. The percent increase in Olsen P from OPR after 12 weeks of incubation averaged 44.5, 39.6 and 36.7% in Entisols, Alfisols and Ultisols, respectively. All the soils responded to OPR, OPR: SSP and SSP application. 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 OPR and OPR: SSP varied from 11.6 to 92.3% (mean 61.3%) and 11.6 to 101.1% (mean 51.4%), respectively. It was concluded that direct application of OPR as P source for soyabean in soils from southwest Nigeria is feasible.