Comparative Study on the Models and Pedotransfer Functions for Estimating of Parameters Describing Soil moisture Characteristic Curve (Case Study: Mahidasht, Kermanshah province)

Although several mathematical models have been proposed to describe the soil moisture characteristic curves, not one model is suitable for all soil types. The purpose of this study was to determine the best model and Pedotransfer function to describe this curve in Mahidasht plain, Kermanshah province. Soil samples were collected from four locations at three depths. The soil moisture characteristic curve of the samples was determined using sandbox and pressure plates. The coefficients of van Genuchten and Brooks-Cory were determined based on measured data using RETC software. The estimated curve by RETC software was compared with the curve drawn based on measured data. The results showed that all models have almost the same estimations and only the Brooks-Corey model overestimates the moisture at low suctions. Based on the results, it can be stated that among the four studied models, the van Genuchten-Bordin model with m = 1-2/n (RMSE = 0.01 and ME = 0.002) is the most suitable model in the study area. The results also showed that the studied Pedotransfer functions have acceptable accuracy for estimating the soil moisture characteristic curve and the modified Sepaskhah-Bondar model (RMSE = 0.1 and ME = 0.02) is the best Pedotransfer function for soils of the Mahidasht. Then the parameters of the most suitable PEDOTRANSFER function for the soils of the study area were calibrated. Although the results of this study can be useful for use in other soils, the coefficients of these functions should be calibrated in each region.