evaluating swap model for simulation of water and solute transport in soil profile

many mathematical models have been applied and developed for simulation of water and solute transport in irrigated agriculture. using a model, it should be first calibrated and validated for different regions. swap is a field scale model that simulates water, solute and heat movement in the soil profile. in this study, the swap model was evaluated for two years (2001 and 2002) on wheat in a semi-arid area in north of gorgan. required data were collected by field experiments. the experiments were consisted of four water quantity levels (50, 75, 100 and 125 percent of crop water requirements) and four water quality levels including s1, s2, s3 and s4 having 1.6, 7.9, 10.8 and 13.6 ds/m in the first year and 1, 9.3, 12.2 and 14.7 ds/m in the second year, respectively. the experimental design was performed by randomized complete block design as a split plot layout with three replications. based on statistical analysis, results from the simulation of swap model were in good agreement with the field measurements of water content (θ), salinity (ece) along the soil profile and wheat relative yield. in all cases, correlation coefficient (r), was higher than 80 percent and root mean square error (rmse) was less than standard division (sd). in the first year, bottom boundary condition was supposed to be free drainage, but due to fluctuations of water table in harvest time, model under predicted soil water content in 80-100 cm depth. since the high frequency of rainfall (especially in second year) and elimination of deep percolation, the discrepancy between the measured and predicted et was not satisfied.