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Optimum use of nitrogen (N) fertilizers is necessary to achieve maximum profitability by farmers and to minimize the risks of environmental pollution. In this study, we used three statistical models to predict the grain yield response of wheat, safflower, and canola to N fertilizer based on combined data from 38 field experiments. Meanwhile, based on the yield response functions and fertilizer-to-product price ratios, the economic optimum N fertilizer rate for each crop for 2009 (before targeting subsidies) and 2015 (after targeting subsidies) was estimated. According to quadratic, exponential, and square root models, 82.5, 90, and 76 kg N ha −1  was estimated to be required for maximum agronomic yield of safflower. More than 300 kg N ha −1  was estimated by all three models to obtain the maximum agronomic yield of canola. In contrast with the government policies for reducing N fertilizer application rates by farmers, due to low fertilizer-to-product price ratios, all application rates of N fertilizer were economic for wheat production even after targeting subsidies. According to the results, to achieve the optimum use of N fertilizers, a proper ratio of the fertilizer cost to the product value should be considered in fertilizer subsidy programs.

communications in soil science and plant analysis

Using Statistical Models to Estimate Economic Optimum Nitrogen Fertilizer Rate for Wheat, Safflower, and Canola before and after Fertilizer Subsidy Programs in Iran