Modeling of response functions and calibration of NPK based on soil fertility for lowland rice grown in Typic Haplustalf

A field experiment was conducted in Madhukur soil series (Typic Haplustalf) at Agricultural College and Research Institute, Madurai to calibrate the NPK requirements for lowland rice var. ADT-36 with and without green leaf manure and ZnSO₄ based on the soil fertility status. The grain yield data was fitted in exponential, quadratic and linear models for functional relationship of crop response to added nutrients. The grain yield data were also subjected to Mitscherlich-Bray equation for finding coefficient of efficiency factor for soil (c) and added fertilizers (c₁). Results indicated that the coefficient efficiency of soil was increased by the application of green leaf manure and ZnSO₄ with an increase of 61.6, 16.9 and 40.1% for soil N, P and K, respectively, further the fertilizer efficiency was also increased to 91, 264 and 163% for N, P and K, respectively. The greater efficiency of fertilizer over soil indicated the more share from the applied nutrients. Based on the soil test value (b), the NPK requirement can be worked out for maximum possible yield by fitting the c and c₁ value in Mitsherlich-Bray equation.