Evaluation of Rock Phosphate-Sulphur Mixtures as Source of Phosphorus to Soybean

Phospbate release pattern of rock phosphate-sulphur mixtures and its agronomic evaluation was studied following incubation and pot culture experiments in a slightly acidic soil. The incubation studies revealed that among the sources of rock phosphates, the release of P was in the order: NCRP>MRP>URP. As regards the P:S ratios of the mixtures, 1:2 ratio had edge over other ratios. The pre-incubated mixtures of rock phosphate and S applied to the experimental soil recorded higher extractable P (0.5 N NaHCO₃) than soil treated with non pre-incubated mixtures. Dry matter yield data revealed that exotic source NCRP was superior to MRP and URP in affecting the drymatter yield of soybean when applied in different ratio mixtures. Phosphate:sulphur ratio of 1:2 was substantially effective with respect to acidifying effect of S on rock phosphate dissolution and consequently the uptake of phosphorus and plant biomass. Further, the interactions between sources x phosphorus levels, sources x P:S ratios and P:S ratio x P levels were also found significant with respect to dry matter yield and P uptake.