Evaluation of CROPWAT model in deficit irrigation management of wheat and barley in Karaj

Deficit irrigation technique can be used for produce more yield for every unit of irrigation water, and cause to increase crop economical benefit. Main purpose of deficit irrigation is high water use efficiency with decreasing in irrigation sufficiency. In this research potential of CROPWAT model in deficit irrigation management for two crops, wheat and barley in Karaj climate was studied. The results of reliability index such as RMSE and CRM with about are 9.8-17.2 percent and 0.32-0.51 value respectively, showed that the model in both crops underestimated the yield reduction compared with actual data. Negative values of EF index achieved for both crops with 14 days irrigation interval show inefficiency of model in yield reduction predicting in this irrigation interval. This difference was more obvious in deficit irrigation treatments. Considering only drought stress and neglecting other stresses -such as salinity- is the most important limitation of CROPWAT model. Model crop coefficients could also caused differences between actual data and model results. This study shows that application of CROPWAT model without calibration of crop coefficients and soil characteristics would be result in significant errors and this is should be considered. In this study water use efficiency for studied crops were achieved in the range of 1.3-2.3 Kg/m3 and maximum values of that was in 20% deficit irrigation. Applying optimum deficit irrigation management could have considerable role in increasing water use efficiency.