Full Length Research Paper

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

Hamid Reza Fooladmand* and Sahar Hadipour

Department of Irrigation, Marvdasht Branch, Islamic Azad University, Marvdasht, Iran.

*Corresponding author. E-mail: hrfoolad@yahoo.com .

Accepted 13 July, 2011

 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 (q_wp) must also be available for this model. In this study, we considered two conditions for entering the q_wp in the model: using measured q_wp and estimated q_wp 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 q_wp 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.