Comparison of modified Mitscherlich and response plateau models for calibrating soil test based nitrogen recommendations for rice on typic ustropept

Use of the right amount of nitrogenous fertilizer is fundamental for farm profitability and environmental protection. For efficient fertilizer use, it is necessary to have information on the optimum rates under different soil-climatic conditions. Curve fitting techniques are often used to estimate optimal fertilizer rates, but a significant problem exists in selecting a proper model for a particular soil-cropping situation. The objective of the work reported here was to compare and evaluate the linear and quadratic response models with yield plateau specifications and modified Mitscherlich's equation. The three models gave good fit to the data when evaluated by R-2. Even though all three models predicted nearly the same maximum yields, the fertilization recommendations estimated by linear response plateau (LRP) and quadratic response plateau (QRP) models were considerably lower than that given by modified Mitscherlich's equation and also the systematic bias with Mitscherlich's model was higher. It is suggested that the yield plateau considerations should be given serious attention in response analysis to avoid the excess use of nitrogenous fertilizers than the actual need. Between the two plateau models, the QRP based recommendations were lower than those of LRP.