Soil Test Crop Response Calibration Studies on Onion (Allium cepa) in Alfisols

Soil Test Crop Response (STCR) calibration studies were conducted with onion (Nasik Red) as a test crop in Alfisols of Andhra Pradesh during rabi 1998–99. In targeted yield approach for calibrating and formulating fertilizer recommendations, the basic data computed were (i) nutrient requirement in kg q⁻¹ of produce, grain or other economic produce, (ii) the per cent contribution from the soil available nutrients (% CS), and (iii) the per cent contribution from the applied fertilizer nutrients (% CF). The nutrient requirement (kg q⁻¹) of N, P₂O₅ and K₂O were found to be 0.26, 0.22 and 0.20, respectively for producing one quintal of onion bulb yield in Alfisols. The contributions (%) from soil and fertilizer nutrients in an Alfisol were found to be 21.31 and 44.37 for N, 25.38 and 27.71 for P, and 5.76 and 48.57 for K, respectively. The fertilizer adjustment equations and ready reckoner for interpolating optimum fertilizer doses at varying soil test values for attaining yield targets of 200 and 250 q ha⁻¹ of onion bulb have been developed.