Evaluation of Pedotransfer Functions for Estimating the Soil Water Contents at Field Capacity and Wilting Point in Central Chile.

Computing the soil water availability and water depth to be applied by irrigation requires the use of the soil water contents at field capacity (FC) and wilting point (WP). Many indirect methods have been developed for estimating the water content at FC and WP. Most of these methods, also known as Pedotransfer functions (PTFs), uses soil properties such as particle size distribution, bulk density, and organic matter content to predict the water contents. Because PTFs are often developed empirically, their applicability may be limited to the data set used to define the method. Therefore, the objective of this study was to evaluate six PTFs developed by Gupta and Larson (1979) and Rawls et al. (1982, 1983, 2004) for predicting the soil water contents at FC and WP in soil from Central Chile. Four PTFs were used for predicting the soil water contents at FC and two for predicting the water contents at WP. The evaluation of the PTFs in this study used a data set of 1112 soil samples from a national soil survey database covering a wide range of textures within Central Chile. The data set includes particle-size distribution, organic matter content, bulk density, and the moisture contents at FC and WP. Without calibration, and depending on the PTF, the moisture contents were predicted with an R² between 0.26-0.54 and 0.45-0.52 for FC and WP, respectively. After calibration, the moisture contents were predicted with an R² between 0.54-0.68 and 0.45-0.54 for FC and WP, respectively. This paper discusses the applicability and accuracy of these PTFs in the study area, and the convenience of calibration when used for soils different to those used to define the method.