Soil Water Balance, Sowing Date and Wheat Yield Using AquaCrop Model under Rainfed and Limited Irrigation

Simulation models of the effect of water on crop yield are valuable tools for improving on-farm water management and water productivity. The AquaCrop model has recently been developed by the FAO to predict crop productivity, net water requirements, and water use efficiency for different scenarios, including rainfed and limited irrigation. The model is suitable for evaluating different regions and crops. The present research examined the efficiency of the AquaCrop model for simulating yield, soil moisture content, and crop canopy response to water availability for wheat in rainfed areas. The region under study in Iran was the upper Karkheh River basin in the Selseleh region of Lorestan province during 2005-2007. The on-farm trials included three irrigation treatments (rainfed, single irrigation only at planting time, single irrigation only in spring). To evaluate the model performance and accuracy of prediction, maximum error, normalized root mean square error, and index of agreement were computed from observed and simulated variables (grain yield, soil moisture content, evapotranspiration). The reliability index of normalized RMSE was 8.34% to 10.56% and of efficiency was 0.78 to 0.93. This indicates that the model was able to accurately simulate soil water content of the root zone, grain yield, and crop canopy under research conditions when compared with field data. The d-statistic indicates that the closer the index value is to unity, the better the agreement between the two variables compared and vice versa. The AquaCrop model for estimation of sowing date under rainfed conditions was not efficient because it required a minimum value for precipitation. The model performed satisfactorily for simulation of grain yield, soil water content, and crop canopy for the rainfed and limited irrigation treatments. The AquaCrop requires minimal input data that is readily available or can easily be collected, making it a user-friendly option for users.