Visualizing nutrient synergies: STCR approach towards NPK balancing and yield targeting in barnyard millet

Achieving higher productivity and long-term sustainability in millet-based systems requires precision nutrient management that considers soil variability, crop demand, and soil health. Barnyard millet (Echinochloa frumentacea), a climate-resilient, short-duration, and nutrient-rich crop, is commonly cultivated under low-input conditions but has considerable potential when grown under balanced fertilization. The study aimed to develop and validate Soil Test Crop Response (STCR)-based fertilizer prescription equations for barnyard millet, enabling precise NPK management with and without farmyard manure (FYM), and to compare their performance with conventional recommendation methods. A three-year field program (2022-2024) was conducted on Alfisols at the Zonal Agricultural Research Station, UAS Bangalore, involving fertility gradient establishment, test crop trials, and validation experiments.

Key parameters including nutrient requirement, soil contribution, fertilizer efficiency, and FYM contribution coefficients were derived to formulate STCR equations for targeted grain yields. Treatments compared STCR-NPK, STCR NPK + FYM, general recommended dose, soil fertility rating approach, and absolute control. Results indicated that STCR-based prescriptions achieved the targeted yield within ± 10% variation. Integrated application of NPK and FYM under the STCR approach recorded the highest grain yield (28.1 q ha⁻¹), with N, P and K agronomic efficiency reaching about 37-49, 62-64 and 93-107 kg grain kg⁻¹ nutrient applied, respectively, and recovery efficiency improving to about 1.35-1.65, 0.66-0.76 and 3.14-3.14 kg kg⁻¹, thereby surpassing conventional recommendation methods. Although the value-cost ratio decreased slightly due to FYM cost, soil fertility, nutrient balance, and long-term system resilience improved. Nitrogen had the greatest impact on yield increase, but balanced NPK combined with FYM ensured superior productivity and nutrient-use efficiency.

The STCR approach with FYM integration enhances soil fertility, nutrient-use efficiency (higher RE and PFP for NPK vs. GRD/soil rating), and system resilience while achieving targeted yields within ± 10%. This provides a viable pathway for sustainable millet intensification across agroecological conditions.