Soil test crop response based fertilizer calibration and soil nutrient forecasting for aerobic rice on Alfisols of Southern India

The Soil Test Crop Response (STCR) approach integrates indigenous soil nutrient supply with crop requirements for site-specific fertilization. While vital for water-efficient aerobic rice, STCR-based precision frameworks for Alfisols in Southern India remain under-researched, representing a significant knowledge gap. In this context, Field experiments were conducted to develop and validate targeted yield and post-harvest soil test value (PHSTV) prediction equations. The results revealed that to produce one quintal of grain, 1.85, 1.14, and 2.70 kg of N, P2O5, and K2O were required under NPK alone, whereas 1.77, 1.09, and 2.88 kg were required under the integrated approach with poultry manure. Validation trials demonstrated that STCR-based recommendations for a 65 q ha−1 target achieved grain yields up to 68.85 q ha−1, representing a 29.3% increase over the general recommended dose (53.25 q ha−1) and 41.2% over the soil test laboratory approach (48.76 q ha−1). Furthermore, the STCR approach recorded a superior Benefit–Cost Ratio of 1.61 compared to 1.09 for the general dose. PHSTV prediction equations showed high reliability (R2 up to 0.96 for P2O5), enabling accurate nutrient estimation without constant testing. This study establishes STCR as a precise, economically superior strategy for sustainable aerobic rice production