Evaluation of SWAP Model for Considering the Effect of Irrigation with Saline Water on the Soil Water Content(A Case study: Birjand)

In order to evaluate the agro hydrological model of SWAP3. 03 for estimating soil water content under different qualities and quantities of irrigation water، an experiment was carried out on wheat varieties with three replications during 2005-2006 growing season in the research Field of University of Birjand. The treatments consisted of three water qualities (1. 4، 4. 5، 9. 6 dS/m)، and four levels of irrigation (50، 75، 100 and 125 % of crop water requirement). Water deficit and saline irrigation treatments decreased the accuracy of the model prediction for various growing stages. The best and worst estimates of the soil water content by the model belonged to the full irrigation treatment (I3) with RMSE values of 0. 93 to 1. 37 % and the least irrigation treatment (I1) with RMSE values of 1. 77 to 2. 57 %، respectively. With decreasing salinity، there was greater agreement between the measured soil water content values and those predicted by the model.