Precipitation and Redistribution Impact on Field-Scale Soil Water Dynamics and Their Variation Characteristics.

The relationship between field average soil water content and its variance is of high importance for soil water management, hydrological and crop growth modelling, designing measurement schemes and identifying opportunities to link measured soil water content with remote sensing indices of soil moisture. It is known that the variance of soil water content decreases with increasing soil water content due to increasing hydraulic conductivity, enhanced lateral flow and a tendency to mitigate spatial variability compared to dry soil conditions. Many field measurements taken in this study validated this variability behavior, whereas others yielded large variation under wet conditions. The objective of this study was to identify reasons for the change of the mean-variance relationship as well as temporal changes in the variability structure and the dominating scale of variation. The relationship of soil textural properties with soil water content was of great interest as well. A field study was conducted in a Crider silt loam soil in Princeton, in western Kentucky between 2007 and 2010. Soil water content was measured using a Diviner capacitance probe at 45 locations along a 450-m transect. At each location, scaled frequency was measured at 10-cm-depth intervals between 0 and 80 cm depth and converted to soil water content through a site- and depth-specific calibration procedure. Soil water content was measured in approximately 2-week intervals during the growing season and longer intervals during the winter season, resulting in 45 spatial data sets. The variance behavior was analyzed using semivariography and Fourier-based transformations, i.e., spectral and wavelet analysis. Under medium-wet to dry conditions large scale fluctuations dominated the spatial variation whereas smaller variation scales were typical for wet to medium-wet conditions. The results of this study are relevant for field-scale model descriptions of soil water processes, and for linking ground truth observations to remote sensing.