Interpretations of Elemental and Microbial Phosphorus Indicators to Understand P Availability in Soils Under Rice–Wheat Cropping System

In order to address the scarcity of phosphorus nutrient reserves and the variations usually observed in the P nutrient storage in soils, a long-term experiment was targeted to assess the impact of integrated fertilizer schedule on soil phosphorus pools and ecophysiological ratios of phosphorus element. P-related soil enzymes like acid phosphatase activity and alkaline phosphatase activity were improved by 6.53–15.93% and 6.14–11.41%, respectively, over the recommended dose of fertilization. Addition of FYM recorded highest DHA (45.24 µg TPF released g−1dry soil h−1) followed by wheat straw (41.25 µg TPF released g−1dry soil h−1) and green manure (38.98 µg TPF released g−1dry soil h−1). Integrated fertilizer schedule improved the microbial biomass phosphorus content by 8.97–29.72% as compared to 100% recommended dose through mineral fertilizer. In the integrated system, only 5–7% of the organic phosphorus was ascribed to microbial biomass, reflecting the accumulation of organic P forms. Higher ratio of DHA (0.20) and pyrophosphatase (0.23) to microbial C in integrated treatments confirmed that the enzyme activities were from extracellular enzymes released by microorganisms. The lower ratios of alkaline or acid phosphatase to pyrophosphatase indicate domination of phosphomonoesters in the P pools. These ratios are important to understand the P availability in soil systems especially under the integrated fertilization schedule.