Evaluation of SWAP Model for Simulating Corn Yield and Water Productivity under Different Conditions of Irrigation Water and Nitrogen Fertilizer Management

The purpose of this research was to evaluate the SWAP model in simulating the yield and water productivity of corn under different conditions of irrigation water and nitrogen fertilizer management. For this purpose, the data from two separate research projects were used. In the first research project, fertilizer in four levels (N1: 100, N2: 80, N3: 60 percent of fertilizer requirement and N4: control) and fertilizer splitting (T1: three and T2: four equal splitting) and in the second project, the factors of irrigation water amount in four levels (W1: 120, W2: 100, WI3: 80 and W4: 60% of water requirement) and nitrogen fertilizer in four amounts (N1: 100, N2: 80, N3: 60 and N4: zero percent of fertilizer requirement) were considered. The results showed that the SWAP model for simulating yield and water productivity in the first project provided low (0.55 ton.ha-1) and acceptable (0.25 kg.m-3) errors, respectively, and in the second project has low (0.51 ton.ha-1) and high (0.47 kg.m-3) error, respectively. The accuracy of this crop model for simulating the yield and water productivity in the first project was in the excellent (NRMSE≤0.1) and good (0.1<NRMSE≤0.2) categories, respectively, and in the second plan, in the excellent (NRMSE≤0.1) and poor (NRMSE<0.3) categories, respectively. Splitting of nitrogen fertilizer from T1 to T2 caused a decrease in yield simulation error from 6.6 to 4.4% and water productivity from 6.6 to 0.4%. The yield simulation error in treatments N1 to N4 were 0.11, 0.12, 0.14 and 0.17 percent, respectively and in treatments W1 to W4 were 0.12, 0.18, 0.12 and 0.12 percent, respectively. There was no proper trend between the changes of water productivity error in different treatments. Based on the results, application of the SWAP model is suggested for the presence of nitrogen fertilizer.