Performance of AquaCrop model for cotton growth simulation under film-mulched drip irrigation in southern Xinjiang, China

AquaCrop is a model of crop growth for predicting responses to various scenarios such as climates and irrigation strategies. Few studies, however, have assessed the applicability of AquaCrop for cotton under film-mulched drip irrigation in salt-affected soil. The objectives of this study were to test AquaCrop performance and to determine the appropriate irrigation amounts for cotton under several scenarios of initial soil-water content (SWC) and soil salinity for two typical soils in a saline region of southern Xinjiang of China with film-mulched drip irrigation. A four-year irrigation experiment was conducted in 2012, 2013, 2015, and 2016 growing seasons for cotton, covering full (100%), over (115 and 145% of full) and deficit (55-90% of full) irrigation treatments. Based on the recommended parameters for cotton in AquaCrop manual, the model was calibrated using 2016 data sets and validated using the data sets from the other three years. Simulations of canopy cover, soil water storage of the root zone and aboveground biomass fitted well with the field observations with coefficient of determination r2 > 0.77 and the index of agreement d > 0.92 and slightly underestimated yield. As for soil salinity, the model gave a reliable simulation for less than 80% of full irrigation treatments, while underestimated for over 80% of full irrigation treatments. Overall, AquaCrop can be used as a feasible tool to predict cotton growth response to water under film-mulched drip irrigation in this region. According to the principle of high yield and WUE, the simulation results showed that the appropriate irrigation amounts were recommended at 358-457 mm for silty loam and 406-462 mm for sandy loam in this region, which can provide a reference for irrigation optimization under film-mulched drip irrigation in southern Xinjiang and other similar regions.