Three-dimensional mapping of clay content in alluvial soils using hygroscopic water content

The three-dimensional (3D) spatial distribution of soil clay content or texture is important to water and solute (e.g., salt and pollutants) transport studies, land planning, and remediation of contaminated soils. However, accurate soil texture analysis is costly and time-consuming. The objective of this study is to map the 3D spatial distribution of clay content in alluvium using easily measured hygroscopic water content data as source data. A total of 542 soil samples were collected from 57 soil profiles within a piece of farmland of 1.68 ha near Tai’an city in the North China Plain. Hygroscopic water content was measured for all samples, but clay content was determined only for 106 randomly selected samples (from 13 soil profiles). Clay content data of other 436 samples were derived using a recently established model for the relationship between clay content and hygroscopic water content. 3D ordinary kriging was applied to map the spatial pattern of soil clay content. Results showed that: (1) spatial correlation ranges of soil clay content are 55.0 and 1.16 m in the horizontal and vertical directions, respectively, and (2) the subsoil clay content is low in the northeast part of the study area, while the soil layers with high clay content are mainly distributed in the upper section of soil profiles in the southern part of the study area. This reflects that the fluvial deposits in the study area have a fining-upward tendency. Cross-validation showed that the 3D kriging method could effectively capture the spatial distribution characteristics of soil clay content in alluvial soils in the North China Plain.