Assessing rice yield response relative to soil phosphorus fractions under site-specific nutrient management

Abstract

In rice-wheat systems on Indian Vertisols, efficient phosphorus (P) management is pivotal for sustaining productivity under resource constraints. This study evaluated STCR-based fertilizer prescriptions, with and without farmyard manure (FYM), across yield-target regimes in a randomized block design with four replications and five treatments. Soils were fractionated to quantify major inorganic P pools (Ca-P, Red-P, Fe-P, Al-P, RS-P) and total P, while plant tissues and grain yield provided P uptake data; P balance was estimated to gauge soil fertility status under different regimes. The STCR dose targeting 22 q ha−1 consistently produced the highest grain yield and total P uptake, accompanied by increases in Ca-P and Red-P pools. FYM enhanced nutrient-use efficiency and amplified certain P fractions, though interactions with inorganic fertilizers varied across treatments. Across fractions, total P and its components rose with cumulative P inputs, aligning with improved P availability and uptake in rice and subsequent wheat. Regression analyses identified Red-P as the strongest predictor of grain yield, followed by available P fractions, with Total-P explaining less variation. Positive P balances under STCR strategies indicated sustained P supply, though regional and long-term validations are recommended. The findings underscore the value of STCR-based P management, particularly when integrated with FYM, to optimize P partitioning, yield targets, and soil fertility in Indian Vertisols; implications for on-farm soil testing, economic feasibility, and broader adoption warrant further investigation.