Corn Irrigation Scheduling and Determination of Water and Nitrogen Fertilizer Production Functions Using The Calibrated AquaCrop Model

Corn is one of the most important grain crops in the world. Corn yield and production is highly dependent on water and nitrogen availability. In this study, the calibrated AquaCrop model, using data collected from a research study in Seed and Plant Improvement Institute, Iran, was used to determine the appropriate irrigation amount and nitrogen fertilizer level under field conditions during 2008-2010. In addition, irrigation-yield, fertilizer-yield and irrigation-fertilizer-yield production functions were determined in order to quantify the results. Hence, yield and water use efficiency of corn were simulated by the AquaCrop model under different irrigation amounts (at levels of 30 to 120% of water requirement) and nitrogen fertilizer treatments (at four levels of 100, 80, 60 and zero percent of fertilizer requirement). The results showed that by providing 80% of the total crop irrigation requirement, acceptable amount of yield and water use efficiency will be achieved. However, crop yield and water use efficiency were improved by increasing fertilizer application rate. Results demonstrated that, corn grain yield in W3 treatment was equal to 11, 10.8 and 10.2 ton ha-3 under 100, 80 and 60% fertilizer treatments, respectively. Also, the obtained Water use efficiency of these treatments was equal to 1.45, 1.53 and 1.36 kg m-3, respectively. In addition, a simple form of production functions for both irrigation-yield and fertilizer-yield simulation models were recommended. However, for irrigation-fertilizer-yield production function, the quadratic form was the best suited model among others.