evaluation of pedotransfer functions and effect of organic matter in prediction of soil saturated water content

abstract saturated water content is one of the important parameters which its measurement is necessary in estimation of soil water retention and unsaturated hydraulic conductivity curves. in several researches, saturated water content is assumed to be equal to soil total porosity. in some others, its value is estimated by pedotransfer functions using readily available parameters, such as bulk density and soil textural data. the objective of this study is to evaluate different presented methods in the literature in estimation of saturated water content. since soil organic matter is considered as an effective parameter on the soil structure, in this study its influence in the estimation of saturated water content is studied. for this purpose, in the first case without considering the value of organic matter, different methods such as soil total porosity, vereecken et al., mayr and jarvis, and scheinost et al., were evaluated. in the second case, the measurement of organic matter was used in prediction of saturated water content. then beside the other methods mentioned above, wösten et al. model as well as two linear and nonlinear models of rajkai et al. were evaluated as well. in the first and second cases 443 and 309 soil samples from three data bases e.g., cornelis et al., unsoda and grizzly were used, respectively. the results showed that when organic matter increased, saturated water content increased as well. in the first and second cases, the smaller values of rmse and aic showed that the vereecken et al. model predicted saturated water content more accurately than the other methods. the obtained results also indicated that models in which organic matter is considered as an input parameter could not estimate saturated water content as accurately as vereecken et al. model estimated.