Assessment of targeted yield equations integrating conventional and nano di-ammonium phosphate (DAP) fertilizers for maize productivity in alfisols of the Southern Transition Zone, Shivamogga, Karnataka

Efficient nutrient management is essential to enhance maize productivity while conserving soil fertility. Soil test crop response (STCR)-based targeted yield equations enable soil- and yield-specific fertilizer recommendations; however, their validation across agroclimatic zones and with emerging inputs, such as nano di-ammonium phosphate (nano-DAP), remains limited. This study evaluated the transferability of STCR prescriptions using conventional fertilizers, nano-DAP and farmyard manure (FYM) in farmers' fields in the Southern Transition Zone (STZ) (Shivamogga), Karnataka. A rabi 2024 verification trial was conducted using the maize hybrid MAH 14-5 in a randomized complete block design (RCBD) with seven treatments: STCR targets (90 and 100 q ha-1) ± FYM, general recommended dose (GRD), soil fertility rating (SFR) and control. STCR NPK + FYM (100 q ha-1) recorded the highest kernel yield (97.82 q ha-1) and stover yield (145.75 q ha-1), along with maximum nitrogen (N), phosphorus (P) and potassium (K) uptake (302.72, 23.48 and 155.98 kg ha-1, respectively). Integrated STCR + FYM treatments also achieved a superior response yardstick (24.00 kg kg-1) and improved nutrient-use efficiency indices (AE-N: 40; RE-N: 0.70). All treatments recorded value cost ratio (VCR) > 2, confirming the economic feasibility of the integrated treatment. Nutrient balance analysis indicated positive K balance but consistent P depletion and variable N balances, highlighting the need for organic amendments. Soil test crop response -based nutrient management, particularly when combined with FYM and nano-DAP, improved yield, nutrient uptake and efficiency, demonstrating its applicability across zones and emphasizing the need for long-term P management strategies.