Soil texture and particle-size distribution as input to estimate soil hydraulic properties

Abstract

This chapter provides an overview on the way soil texture can be characterized and described, the way those data are considered in different pedotransfer functions (PTFs), and the methods that can be used to fill in missing data required by some PTFs. It also presents a study that compares different representations of soil particle-size distribution (PSD) in estimating soil water retention. Textural classification of soils is based on particle-size analyses in most parts of the world. A number of standards exist internationally for the description of soil PSD and particle-size classes. Soil texture classes are defined based on sand, silt, and clay content limits and are usually displayed in soil texture diagrams. Even when the same particle-size class system is used, texture class definitions may differ. Soil-texture-class information is primarily used as input to class PTFs. A class PTF does not use detailed particle-size data as input but gives calculated, usually averaged, values of the output variable in a tabular format for each soil class/unit. Detailed PSD and/or parameters derived from it are used in almost all PTFs. The chapter compares the usefulness of some of the most common representations of PSD in estimating water retention at -−10, −33, and −1500 kPa and the available water content (AWC) of the soil, which is defined as the difference between water contents at −33 and −1500 kPa matric potentials. To relate the above soil hydraulic properties to soil texture, a number of PTFs are developed using three databases and the group method of data handling (GMDH). The GMD and its standard deviation are also used as predictors.