Parametric pedotransfer functions of a simple linear scale model for soil moisture retention curve

Abstract

Soil moisture retention (SMR) curve is a basic soil property. Since, direct measurement of the SMR curve is costly and time-consuming; it can be estimated using pedotransfer functions (PTFs) based on more easily available soil properties. Parametric PTFs estimate the parameters of a closed-form analytical equation for representation of SMR curve. In this study, we derived parametric PTFs for the model of Groenevelt and Grant (2004) which include three adjustable fitting parameters (K0, K1 and n). Our results tended to consider the constant value of 5 for the parameter of K0, and the parameters K1 and n were estimated based on more easily available soil properties by using twenty-two soils. The value of soil water content at matric potential of 1500 kPa (qwp) must also be available for this model. In this study, we considered two conditions for entering the qwp in the model: using measured qwp and estimated qwp with more easily available soil properties considering sand fraction of the soil, organic matter content, geometric mean particle-size diameter and geometric standard deviation of the particle-size diameter. Finally, the derived PTFs were evaluated for eight independent soils. The results indicate that there was no considerable difference between the two mentioned conditions for using qwp to estimate the SMR curve. Also, the results demonstrated that the proposed model in this study can be used for estimating the SMR curve with acceptable accuracy. Key words: Model of Groenevelt and Grant, soil moisture retention curve, pedotransfer functions.