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Crop growth simulation models have become important tools to assess and develop deficit irrigation strategies especially in arid and semi-arid regions. In this study, we tested the ability of the FAO developed AquaCrop model (V 4.0) to simulate canopy cover (CC), actual evapotranspiration (ETcact), total soil water content (TWC) and grain yield (GY) for winter wheat under flood irrigation in the semi-arid region of Tensift Al Haouz, Marrakech (center of Morocco). The simulation was performed at a daily time step, using thermal units, i.e., growing degree days (GDDs) during two successive growing seasons: 2002/2003 and 2003/2004. Firstly, the calibration of the model was performed on three fields during 2002/2003 cropping season. Various parameters affecting CC, ETcact,TWC and GY have been calibrated based on the comparison between measurements and the results of simulations. Afterward, the validation was done on six fields during the 2003/2004 cropping season. The results showed that the model simulates reasonably well CC, ETcact, TWC and GY over two growing seasons. The average values of the Mean Bias Error (MBE) between observed and measured CC, ETcact,TWC and GY were -4.6%, -0.23 mm/day, 17.56 mm and 0.05 t/ha for the calibration fields, and 7.89%, -0.01 mm/day, 0.5 mm and 0.06 t/ha for the validation fields, respectively. Additional statistical parameters like the root mean square error (RMSE) and the Nash-Sutcliffe efficiency (NSE) showed also that the model gives acceptable estimates of CC, ETnct, TWC and GY.

After accurate calibration and validation of the AquaCrop model, it was used for irrigation scheduling based on the threshold of the root zone water depletion (D-r,D-threshold) over two fields with contrasted sowing dates. The various simulations (irrigation scenarios) showed that early sowing is more adequate than late sowing in saving water and obtaining adequate grain yield. It has been also shown that the value 0.6 of D-r,D- threshold can be used as an appropriate threshold of water depletion to improve the wheat irrigation management. Consequently, the AquaCrop model can be considered as a potentially useful tool for planning irrigation schedules on an operational basis in the arid and semi-arid regions. (C) 2015 Elsevier B.V. All rights reserved.