Fitting Different Models of Soil-Moisture Characteristic Curve on 30 Soil Samples in Fars Province

Background and Objectives: Soil moisture characteristic curve is one of the most important soil hydraulic properties, and shows the relation between soil suction and soil moisture content. Direct measurement of this curve is costly and time-consuming. Therefore, an alternative to measurement is to estimate this curve using the more easily available soil properties. On the other hand, many models have been presented for fitting to measued data of this curve. However, their fitting ability on different kinds of soil have been rarely investigated.
Materials and Methods: In this study, 30 measured surface soil samples with high variaty texture from the depth of 0 to 30 cm in different regions of Fars province have been used. Selected soils were classified into three textures of fine, medium and coarse. Then, 10 useful soil moisture characteristic curve models (Gardner, Brooks and Corey, Campbell, van Genuchten, Tani, Boltzman, Feremi, Fredlund and Xing, Groenevelt and Grant and Dexter et al.) were fitted on the data, and the parameters of each medel in each soil sample were determined, and then the most appropriate fitted model in each soil group was determined. To determine the best model, the combination of statistical equations and linear correlation was used, and then the value of mean square deviation (MSD) was calculated to evaluate the different models for fitting soil moisture characteristic curve.
Results: The results indicated that the fitted models were better in medium texture group than the fine and coarse texture groups. The results showed that in fine texture group the models of Brooks and Corey, Campbell, van Genuchten, Fredlund and Xing, Groenevelt and Grant and Dexter et al., in medium texture group the models of Gardner, Groenevelt and Grant and Dexter et al., and in coarse texture group the models of Gardner, van Genuchten, Groenevelt and Grant and Dexter et al. were appropriate. Consequently, the results according to the MSD values indicated that the model of Dexter et al. was the most appropriate model for fitting to the measured data of soil moisture characteristic curve. Furthermore, the results of this study showed that the famous model of van Genuchten was good for futting to the measured soil moisture characteristic curve data. On the other hand, the models of Tani, Boltzman and Feremi were not appropriate.
Conclusion: The results of this study investigated that the model of Dexter et al. was better than the other models for three textural group (fine, medium and coarse) for 30 soil samples of Fars province. Also. similar results have been reported by other investigators for the soil samples in Gilan province.