Evaluation three fractal model to determine soil water retention curve

Abstract
Soil hydraulic parameters (soil water retention curve) is a fundamental soil property employed to quantify plant available water and for modeling water and solute movement in soils that the determination of this property via direct methods is expensive and time consuming. For solve this problem Indirect methods have been proposed that fractal analysis is one of the methods. Pore- Solid Fractal model was used for modeling soil structure and soil water retention function by many researchers. PSF model is a public expression for maintenance function soil water that is provided by other researchers in special form. The aim of this study was to assess PSF public function based on fractal dimension of soil water suction data and comparison with Brooks- Corey and Tyler-Wheatcraft models. In this study, with using laboratory data from unpublished sources, obtained soil water retention curve for soils under investigation by the PSF, special cases (Brooks-Corey and Tyler-Wheatcraft).To verify the results, a comparison between the predicted and measurement soil water content for many soil of UNSODA database. The results showed that for the soils investigated Tyler–Wheatcraft function were better match in compared with the PSF and the Brooks-Corey function. To calculate the intake air ( ) and soil saturation ( ),using any of the equations PSF, and Tyler and Wheatcraft, and Brooks-Corey not significantly different from each other. But for calculating the fractal dimension (D) using Eq Tyler-Wheatcraft was recommended. Empirical simple models was developed with ready available data by relationship between the geometric mean (dg) and geometric standard deviation (σg) with  ,  and . Then, soil water retention curve was calculated For many soil of UNSODA database. Regardless texture soil, all predicted and measured volumetric soil moisture were compared with a one-to-one. The result showed no significant difference between the predicted moisture content ( ) and measured ( ) with a one-to-one. So it seems that the empirical simple model is able to estimate soil water retention curve with reasonable accuracy.