Comparison Eight Methods for Estimating Soil Moisture Characteristic Curve Based on Two Methods for Estimating Soil Particle Size Distribution Curve

The relationship between soil moisture and soil matric suction is called soil moisture characteristic curve, which its measurement is time-consuming and expensive. One of the estimation methods of soil moisture characteristic curve is using the soil particle size distribution curve and bulk density which contains a scaling parameter (α). In this study, 10 soil samples were selected from Marvdasht region in Fars province, and soil texture and soil moisture characteristic curve of each soil were measured. Then, the soil particle size distribution curve of each soil was estimated based on Fooladmand and Sepaskhah model (FS) and Fooladmand and Mansuri model (FM), and also eight methods were used for determining the scaling parameter including linear procedure with constant void ratio (N), logistic procedure with constant void ratio (G), linear procedure with local void ratio (LN), logistic procedure with local void ratio (LG), Alfa-1 (A1), Alfa-2 (A2), Alfa-3 (3) and Alfa-4 (A4). Therefore, the soil moisture characteristic curve of each soil was estimated with 16 different methods, and all of them were compared with measured soil moisture characteristic curve data. For this purpose, Standard error (SE), geometric mean error ratio (GMER) and geometric standard deviation of the error ratio (GSDER) were used. The results sowed that the FM model for estimating the soil particle size distribution curve and then estimation the soil moisture characteristic curve was better than the FS model. In general, the results indicated that the procedures of FM-A1, FM-A2, FM-A3, FM-N and FM-LN were appropriate for estimating the soil moisture characteristic curve.