Assessment of the AquaCrop Model for simulating Canola under different irrigation managements in a semiarid area

Field experiments were conducted in 2005-2006 and 2007-2008 and the data were used to calibrate and validate yield and biomass of AquaCrop Model for canola (Brassica napus l.). The model was calibrated with the first year and then was validated with the second year data. Five water stress treatments at different growth stages were performed including fully irrigated during whole growing period (I1), water stress at vegetative stage in spring (I2), water stress at flowering stage (I3), water stress in grain filling stage (I4) and severe water stress conditions during whole growing period with supplemental irrigation in planting and germination stage (I5). AquaCrop model coefficients were calibrated for I1 in 2005-2006 and the calibrated parameters were used for other treatments in both year. In this simulation model was assessed based on measured values of the water content in root zone, evapotranspiration, canopy cover and final yield and dry matter that the latter are the important trait for the farmers The accuracy of the model in calibration was tested using RMSE, NRMSE and d, which were 0.92 t ha , 12.37% and 0.98 for yield and 0.92 t ha-1, 12.37% and 0.98 for biomass, respectively. The RMSE, NRMSE and d values in 2007-2008 (validation year) were obtained as 0.26 t ha-1, 10.01% and 0.92 for yield and 0.84 t ha-1, 14.93% and 0.92 for biomass, respectively. The result of calibration and validation for volumetric water content was acceptable. AquaCrop model estimated the evapotranspiration acceptable in the first year, while the accuracy of model to predict this parameter decreased for validation. Therefore, the model was calibrated effectively for yield and biomass; however, the results were less satisfactory when it came to the simulation of the severe stress (I5).