Use of partially acidulated rock phosphate as a possible means of minimising phosphate fixation in acid soils

Summary To examine the possibility of minimising phosphate fixation the lateritic soil at various levels of liming was incubated with phosphate rock from U.A.R. acidulated to different degree viz. 0, 10, 20, 50, and 100 per cent both with phosphoric and nitric acid. The soil was incubated for 90 days on addition of different phosphate carriers at the rate of 100 ppm total P₂O₅ containing different proportion of water-soluble, citrate-soluble and insoluble phosphorus. Samples were drawn at an interval of 30 days. Bray's p₁ and pH of the soil samples were measured. The dry-matter yield and uptake of phosphorus by two successive crops of maize grown in pots, the treatments being same as in incubation study, were well correlated with the Bray's p₁. Ground rock phosphate and 10 per cent acidulated material were effective in minimising the fixation in soil of pH 4.0 whereas 50 per cent acidulation was suitable for soils of higher pHi.e. 5.6 and 6.5. H₃PO₄ acidulated material was proved superior to HNO₃ acidulated product. The use of partially acidulated rock phosphate for acid soils may be recommended to receive economic return. Associate Professor Senior Research Assistant.