Changes in soil phosphorus fractions across nutrient management treatments in rice-wheat cropping sequences

Abstract

This study examines how nutrient management strategies influence soil phosphorus (P) speciation and crop performance in Vertisol-dominated rice-wheat systems. The objectives were to quantify shifts in soil P fractions, relate these fractions to P uptake and available P, and evaluate yield responses under diverse P regimens. A factorial experiment with five treatments and four replications tested inorganic NPK doses, STCR-based yield targets (14, 18, and 22 q ha−1), and farmyard manure (FYM). Soil samples were fractionated to quantify major inorganic P pools (Ca-P, Red-P, Fe-P, Al-P, and Sparing/RS-P) alongside total P, while plant tissues and grain yield provided P uptake data. Regression and correlation analyses revealed that the 22 q ha−1 yield-target STCR doses achieved the highest grain yield and total P uptake, with corresponding elevations in Ca-P and Red-P pools. FYM generally enhanced nutrient-use efficiency and amplified select P fractions, though the magnitude of these effects depended on the interaction with mineral fertilization. Across treatments, total P and its fractions rose with cumulative P inputs, indicating improved P availability and uptake by rice and subsequent wheat. The strongest associations were observed between Ca-P/Red-P stocks and yield, underscoring the linkage between P partitioning and productivity. These findings support the adoption of STCR-based regimens, particularly at higher yield targets, combined with FYM, to optimize P dynamics and sustain productivity in rice-wheat rotations on Vertisols. For broader applicability, region-specific validation and economic assessments are recommended.