PHOSPHORUS FRACTION DYNAMICS IN SOIL AS AFFECTED BY PHOSPHORUS-SOLUBILIZING BACTERIA AND INTEGRATED PHOSPHORUS FERTILIZATION

Abstract

Phosphorus (P) availability in agricultural soils is limited by fixation into mineral and organic pools, reducing fertilizer use efficiency. This study evaluated the capacity of a phosphorus-solubilizing bacterial inoculant (Pseudomonas striata) combined with integrated organic–inorganic P sources to modify soil P fraction dynamics under controlled incubation. Soil (0–20 cm) was incubated in 2-kg units amended with seven treatments (T1 = control; T2 = rock phosphate; T3 = SSP; T4 = compost + RP; T5 = compost + SSP; T6 = bagasse ash + RP; T7 = bagasse ash + SSP) with and without PSB. PSB inoculation and treatment composition significantly affected all measured P fractions and their temporal trends. At early sampling (10 d), integrated SSP + bagasse ash (T7) and SSP + compost (T5) produced the largest increases in labile and moderately labile pools: e.g., ABDTPA-P (T7 = 5.70 vs control 2.74 mg g⁻¹) and Olsen-P (T5 = 8.04 vs control 4.28 mg g⁻¹). Resin-P and ethanol-extractable P followed similar patterns (resin-P T7 = 7.00 vs control 2.49 mg g⁻¹; ethanol extractable P T7 = 0.836 vs control 0.174 mg L⁻¹). Although all P pools declined with incubation time due to sorption and biological uptake, treatments T5, T7 and (in later intervals) T6 retained relatively higher P concentrations at 40–60 d. Across intervals, PSB-inoculated soils consistently showed greater P availability than non-inoculated controls (e.g., mean ABDTPA-P increase ≈ 6–8%), indicating persistent microbial enhancement of P solubilization and labile pool maintenance. The results demonstrate that PSB coupled with SSP blended with compost or bagasse ash significantly increases short-term P availability and prolongs residence of labile P in alkaline soils. Our findings support integrated biological–organic strategies to improve phosphorus use efficiency and provide a mechanistic basis for field evaluation and optimization of PSB-based P management in cropping systems.