Effect of rock phosphate enriched compost and chemical fertilizers on microbial biomass phosphorus and phosphorus fractions

The aim of this research work was to prepare rock phosphate enriched compost using low-grade mineral such as rock phosphate (RP) mixed with rice straw and Aspergillus awamori and to study their effect on microbial biomass phosphorus (MBP), phosphatase activity and phosphorus (P) fractions in a wheat-soybean cropping system. The experiment was carried out in a randomized block design with four treatments namely, control, recommended dose of NPK fertilizers (100% RDF), rock phosphate enriched compost (RPEC) at the rate of (5 t ha-1 and 50% RDF + Rock phosphate enriched compost (RPEC) at 5 t ha-1. Application of RPEC at 5 t ha-1 along with 50% recommended dose of chemical fertilizers (RDF) significantly improved microbial biomass P (MBP) (5.62 and 4.28 mg kg-1 soil) and alkaline phosphatase activity (194.0 and 174.0 μg PNP g-1 soil h-1) in surface (0-15 cm) and sub-surface (15-30 cm) soil respectively, than unfertilized control plot after harvest of wheat. The magnitude of changes of P fractions as well as microbial activities was higher in surface soil than sub-surface soil. Data generated from the field study revealed that phosphorus (P) fractions significantly increased due to application of RPEC either alone or in combination of chemical fertilizers over unfertilized control plot. Application of RPEC plus chemical fertilizers significant increased Olsen P compared to unfertilized control plot after harvest of wheat and soybean. Treatment T4 increased by 68.8 and 58.7% higher Olsen-P over control at 0-15 and 15-30 cm soil depth, respectively after wheat harvest.