Fertilizer Prescriptions Equation for Targeted Yield in Onion under Integrated Plant Nutrient Management System in an Inceptisol

A field experiment was conducted on onion under soil test crop response correlation studies in Varanasi region of Utter Pradesh during rabi 2024-25. Multiple regressions have been calibrated for predicting onion yield through soil and fertilizer nutrients and their interactions. The models were found to have a high and significant predictability value. Using the data, fertilizer adjustment equations have also been developed for prescribing optimum fertilizer doses for attaining different yield targets. Soil test data, bulb yield and NPK uptake by onion were used for achieving four important basic parameters, viz., nutrients required (NR) to produce one quintal of onion bulb contribution of nutrients from fertilizers (% CF), contribution of nutrients from soil (% CS) and contribution of nutrients from organic matter-FYM (% COM). It was found that 0.35, 0.10 and 0.25 kg of N, P₂O₅ and K₂O, respectively were required for producing one quintal onion bulb yield. The per cent contribution of nutrients from soil, fertilizer and FYM were 27.70, 62.37 and 22.08 for N; 12.76, 46.36 and 31.98 for P₂O₅ and 7.72, 4.80 and 6.79 for K₂O, respectively. By using these basic parameters, ready reckoner of fertilizer doses was prepared for varying soil test values and desired bulb yield targets of onion using NPK alone and NPK with FYM.