Spatio-Temporal Processes of Soil Water Storage in a Farmers' Field.

In the past, spatial patterns of field soil water storage have been analyzed based on their temporal stability in field soils. Besides supporting the efficiency of sampling schemes, this method can provide a better understanding for the reasons of spatial variation and spatial relationships of soil moisture patterns to other relevant field processes. The objective of this study was to identify soil water storage temporal stability behavior and its underlying processes in a Crider silt loam soil in Western-Kentucky after deriving a field calibration procedure for a soil water capacitance probe. In the field study, water content access tubes were installed along a catena in 45 locations at every 10 m. Over a period of two years, soil water content measurements were taken in 10-cm increments to a depth of 80 cm at each of the 45 locations at approximately every two weeks. A site-specific field-calibration was developed, and for the first time, the spatially structured process of capacitance probe calibration coefficients was described in its spatial continuity, related with soil clay content and across subsequent soil depths. Over the period of a growing season, the soil water storage (SWS) varied at different scales. Under relatively moist conditions, soil water storage varied at similar scales as the clay content across this catena. The relationship between field spatial mean of soil water storage and its variance was not unique. Similar mean values were associated with a large variance when the time since the previous rainfall event was more than three days ago. When the last rainfall was less than three days ago, the variance for a given mean value was lower. The scale-variant behavior of soil water storage is further elucidated based on temporal stability and Fourier-based transform analysis.