Estimation of the Economic Optimum Rates of Nitrogen Fertilizer for Maize Grown in a Calcareous Soil in Combination with Organic Manure Applications

Non-optimal nitrogen (N) fertilizer application is frequently caused by a producer's uncertainty in projecting the N rate that ensures maximum economic return. In order to determine the optimal N rates for maximum and economical yields, the response of maize (Zea mays L.) grain yields to N fertilizer at different rates of compost were evaluated in a calcareous soil. The treatments comprised four compost levels of 0, 20, 40, and 60 m(3) ha(-1). The N rates were 0, 70, 140, 210, 280, and 350 kg N ha(-1) in three equal split doses. Quadratic response functions were observed when maize grain yields were plotted against N fertilizer rates. According to derivative analysis of the functions averaged across the two seasons, grain yield plateaued at 8189 kg ha(-1) with an N fertilizer rate of 282 kg ha(-1). When the N fertilizer cost to grain price ratio was taken into account, the average economic grain yield was 8077 kg ha(-1) by N fertilizer rate of 248 kg ha(-1). Numerous future scenarios of fertilizer cost to grain price ratios were assumed in order to determine the economically optimal N rates. The scenario of increasing N fertilizer cost by 40% resulted in a decrease in economic optimal N rate by an average of 15.8 kg N ha(-1). However, a 40% increase in grain price resulted in an increase in the economic optimal N rate by 9.4 kg N ha(-1). Due to the high N losses in calcareous soils, increasing the N fertilizer cost scenario is beneficial since it decreases the economically optimal rates, which increases N use efficiency while also decreasing reactive N losses and protecting the environment.