Assessment of combined influence of soil test crop response-based fertilizer recommendations and nano-fertilizers on post-harvest soil fertility in Alfisols of Karnataka

Maize (Zea mays L.) productivity in Alfisols is constrained by low organic matter, nutrient deficiencies and nutrient losses, requiring precision nutrient management. This study evaluated whether Soil test crop response-based (STCR) fertilizer prescriptions integrated with farmyard manure (FYM) and foliar nano-diammonium phosphate (nano-DAP) could improve post-harvest soil fertility across low, medium and high fertility strips at Zonal Agricultural Research Station (ZARS), Gandhi Krishi Vigyana Kendra (GKVK) (Bengaluru) and farmer fields in the Southern Transition Zone (Shivamogga) during Rabi 2024. A randomized complete block design with seven treatments (T1–T7: STCR nitrogen, phosphorus, potassium (NPK) at 90 and 100 q ha-1, STCR NPK+FYM, General recommended dose, Soil fertility rating and absolute control) was used; soil physical, chemical and nutrient parameters were measured pre-sowing and at harvest. STCR combined with FYM (T2, T4) improved soil buffering, in the low fertility strip final pH in T2 was 5.98 compared to 5.70 in STCR alone (T1), a rise of 0.28 pH units and produced modest increases in soil organic carbon (T2: 0.46 → 0.49 %, Δ = +0.03 %). Electrical conductivity increased marginally under fertilizer treatments but remained well below salinity risk (maximum observed ~0.095 dS m-1). Residual nutrients varied by approach: blanket approaches (GRD, SFR) left higher post-harvest N and P (In the medium fertility strip available N in T6 = 309 kg ha-1 vs T2 = 226 kg ha-1, Δ = +83 kg ha-1; available P in T6 = 441.6 kg ha-1 vs T2 = 315.1 kg ha-1, Δ = +126.5 kg ha-1). Potassium depletion was minimized where FYM and STCR were combined. Overall, STCR integrated with FYM and targeted nano-DAP foliar applications enhanced post-harvest soil quality indicators and promoted more efficient nutrient management in Alfisols. These results support adoption of STCR-based integrated nutrient management for sustainable maize production in nutrient-deficient Alfisols of Karnataka.