Performance Evaluation of Pedotransfer Functions to Predict Field Capacity and Permanent Wilting Point Using UNSODA and HYPRES Datasets

Abstract

Using basic soil properties could save time and costs in determining field capacity (FC) and permanent wilting point (PWP). The objectives of this study were to investigate the relationship between FC and PWP and basic soil properties, develop two new equations for estimating FC and PWP, and evaluating their performance as compared to some existing pedotransfer functions (PTFs) in predicting FC and PWP. For this purpose, 210 soil samples of UNSODA dataset and 45 soil samples of HYPRES dataset were used for development and validation of the PTF, respectively. Graphical exploration of relations between soil texture component, geometric mean particle-size diameter (dg), bulk density (BD), and organic matter (OM) with FC and/or PWP showed that relations of FC was nonlinearly related to percentage of clay (positive) and dg (negative) and relations of PWP was linearly and nonlinearly related to percentage of clay (positive) and dg (negative), respectively. Based on standardized independent variable weight (W), dg showed the highest influence on FC (W = 0.81), followed by percentage of clay (W = 0.70), OM and BD (W = 0.49). PWP was primarily affected by percentage of clay (W = 0.89) and dg (W = 0.64), whereas BD and OM with Wof 0.30 were less effective. The two new functions suggested and evaluated for predicting FC and PWP had root mean squares error (RMSE) of 0.06 and 0.02 m3 m−3, geometric mean error (GMER) 1.03 and 1.10 m3 m−3 and Akaike's information criterion (AIC) of −262 and −349, respectively. As such, their prediction performance was higher than that of other FC and PWP PTFs found in literature.