Evaluation of the FAO AquaCrop model for winter wheat on the North China Plain under deficit irrigation from field experiment to regional yield simulation

Winter wheat is the main crop on the North China Plain (NCP), and in this region the most limiting factor for the crop is water. The objective of this study was to adapt and test the ability of the FAO-developed AquaCrop model (v3.1) to simulate winter wheat grain yield, biomass, actual evapotranspiration (ETa) and total soil water content (0–120cm). Field experiments were conducted under deficit irrigation at the Luancheng Agro-ecosystem station (NCP) in 1998–2001, and the AquaCrop model was calibrated with treatment D (1999–2000); the rest of the data was used for validation of the model. The AquaCrop model was revalidated with data on measured grain yield from the experimental station for 1990–2010, considering actual field conditions. The second revalidation was done with the statistical grain yield for 1995–2010 in the study region. For the model validation, the significant differences between simulated and observed grain yield, biomass and ETa were in the order of: rainfed treatment>well-watered treatment>moderate water stress. Total soil water simulated by AquaCrop tends to follow closely the trend in the measured data, but with slight underestimations for irrigated treatments and significant overestimations for rainfed treatments. In general, errors in the model's evaluation such as RMSE and Willmot's d statistics were for grain yield (0.58Mgha−1, 0.92), biomass (0.87Mgha−1, 0.95), ETa (33.2mm, 0.93) and soil water content (24.5–37.6mm, 0.85–0.90). The overall results based on extensive validation and revalidation showed that AquaCrop is a valid model and can be used with a reliable degree of accuracy for optimizing winter wheat grain yield production and water requirement on the NCP.