Assessment of AquaCrop Model for Simulating Yield Response of Corn to Water and Fertility Stresses

Water and fertilizer are the most important inputs for producing agricultural crops. Simulation models that quantify effects of water and fertility on yield at the farm scale are valuable tools in water and irrigation management. The AquaCrop model, which has recently been developed by FAO, predicts crop productivity and water requirement under water and fertility stress conditions. In this research, capability of AquaCrop model in simulation of Corn yield response to different levels of water and fertility was studied in Karaj. A field experiment was carried out in 2008 and 2010 years. A factorial design based on randomized complete block design accomplished with four levels (60, 80, 100, and 120%) of the irrigation water requirement and four levels (0, 60, 80 and 100%) of the recommended fertilizer value. Sensitivity analysis showed that the model was sensitive to initial moisture content, time from sowing to start senescence, Reference harvest index (HIo), normalized water productivity (WP*) and maximum coefficient for transpiration (KcTr) more than other parameters. Results showed that the AquaCrop model was able to simulate the grain yield under water and fertility stress, in both years. The normalized maximum error (ME), normalized root mean square error (nRMSE) and coefficient of determination (R2) were calculated 24.77, 9.27 and 0.92 respectively, in validation year. The model was able to simulate the grain yield and crop evapotranspiration (ETC) in non-water stresses (ME, nRMSE an R2 were 9.9, 6.21 and 0.97, respectively) and non-fertility stresses (ME, nRMSE an R2 were 9.9, 6.21 and 0.97, respectively) satisfactory, but it was not satisfactory in simulating sever irrigation and fertility stress. Most deviations from observed data in severe water treatments (ME, nRMSE an R2 were 24.72, 16.61 and 0.66, respectively) occurred.