Application and Comparison of Parametric Pedotransfer Functions of van Genuchten Model for Transient Water Flow Simulation in a Cultivated Soil

In recent years, using pedotransfer functions (PTFs) has been considerated as a way to estimate the hydraulic properties of soil from easily to measured parameters. In this research, soil water retention curve of a clay loam soil was estimated using some of the global and regional PTFs. Soil water retention curve (SWRC) was constructed using direct measuring methods in laboratory and the validation of PTFs for estimation of the mentioned curve was evaluated. By entering the measured and estimated SWRC to Hydrus-1D, soil water flow was simulated and the accuracy of the PTFs for simulation of water flow was quantitatively compared. The results showed that the functions of Sepaskhah (Sepas), Yaghubi-1(Y-(1)), Yaghubi-2(Y-(2)) and Ghorbani-2(Gh- 2)) with normalized root mean square error (NRMSE) values of less than 0.1 could reasonably predict SWRC of the surface soil. In prediction of SWRC of subsurface soil, the NRMSE values of most global PTFs were less than 0.3 and for most of the regional PTFs were less than 0.2. NRMSE values in simulation of water content of surface and subsurface soils using Hydrus by applying different PTFs were between 0.07 to 0.84, respectively. It can be concluded that in running validating phase one should consider the objective for which the PTFs may be applied.