Optimization of Nitrogen Fertilizer and Irrigation Water Using Response-Surface Methodology (RSM) in Corn Cultivation

The purpose of this research was to determine the optimal amounts of nitrogen fertilizer and irrigation water to achieve maximum yield (Y), water productivity (WP) and fertilizer productivity (FP). For this purpose, the research was carried out on a 370 double cross hybrid corn in the 500-hectare farm of the Seed and Plant Improvement Institute (SPII) for two crop years, using response surface method. The tested factors included the amount of irrigation water at three levels (I1:100, I2:80 and I3:60% of water requirement) and nitrogen fertilizer at three levels (F1:100, F2:60, and F3:0% of fertilizer requirement). The results showed that the model used had an acceptable error for predicting yield (7.3%), water productivity (9.3%), and fertilizer productivity (24%). The accuracy of this model for predicting the desired traits was in the excellent (NRMSE≤0.1), excellent (NRMSE≤0.1), and moderate (0.2≤NRMSE ≤0.3) categories, respectively. The efficiency of the desired model was also favorable (d ≥ 90 and EF≥0.5). By increasing the amount of fertilizer (changing from -1 to +1), the yield also increased, but the rate of yield growth was not linear. The yield changes compared to irrigation water had a more uniform slope and its growth was closer to a linear line. The increase of irrigation water up to the range of +0.8 increased the efficiency of water consumption. Moreover, it reduced the efficiency of water consumption. The changes in the efficiency of fertilizer consumption were positive compared to the two factors of nitrogen fertilizer (up to the range of +0.9) and irrigation water (up to the range of +0.8). The optimal amounts of nitrogen fertilizer and irrigation water were in the range of 60-100% of fertilizer requirement and 70-100% of irrigation water requirement, which after optimization were determined as 71% and 100%, respectively. In these conditions, corn yield, water, and fertilizer productivity were 7 tons/ha, 2.3 kg.m-3, and 33 kg.kg-1, respectively.