INFERRING SUBSURFACE MORPHOLOGY FROM TRANSIENT SOIL MOISTURE PATTERNS USING ELECTRICAL CONDUCTIVITY

Abstract

A non–intrusive survey method was developed that examined the relationships among spatial and temporal variations of soil water content, soil texture, and bulk electrical conductivity (ECa) in a 7.5 ha research watershed in southwestern Tennessee. Our goal was to identify areas that may exhibit rapid movement of subsurface moisture, as this is a precursor of offsite agrochemical migration. The survey protocol identified similar and dissimilar temporal variations in ECa patterns. Repeated spatial measurements of ECa, starting at near field capacity and then progressing through the draining and drying process, supplied visually shifting ECa patterns that correspond to dynamic soil moisture variations and subsurface morphology transitions. We noted that spatial ECa patterns for a field remained somewhat analogous across data gathering events, shifting in relative amplitude along with seasonal moisture levels. For this study, we considered soil morphology constant over the short data acquisition interval, with short–term subsurface moisture variations as the parameter primarily influencing ECa changes. We inferred soil morphology as the major factor for ECa pattern similarity across time. Follow–up soil coring analysis along two separate low–to–high ECa transects supported this assumption for this site.