Simulation of Yield Decline as a Result of Water Stress Using BUDGET Model

In this paper, to account for the effect of water stresses in the various growth stages under deficitirrigation, the multiplicative, seasonal and minimal approaches are integrated in the BUDGETmodel. To evaluate the model, the simulated yields for winter wheat (was grown in Sharif Abaddistrict) under various levels of water stress were compared with observed yields. The resultshowed, simulated crop yields agreed well with observed yields for this location usingmultiplicative approach (in comparison with minimal and seasonal approaches). The determinationcoefficient (R2) between observed and simulated yields ranged from 0.81 to 0.92 with very highmodeling efficiencies. The root of mean square error (RMSE) values is relatively small and rangedbetween 6 to 14. A sensitivity analysis showed that the model is robust and that good estimates canbe obtained by using indicative values for the required crop and soil parameters