Spatial and Temporal Variations in Electrical Conductivity in North Mississippi Loamy Soils

The use of electromagnetic induction (EM) to characterize and quantify spatial and temporal variations in soil properties is appealing due to low operational costs, rapid measurements, and device mobility. EM methods are sensitive to soil electrical conductivity, which can vary with soil moisture, clay content, soil salinity, and the presence of electrically conductive minerals. We are evaluating the controls on EM response in loamy soils present at the University of Mississippi (UM) Soil Moisture Observatory (SMO). The 5 acre SMO is located in a former agricultural field at the UM Field Station, a 740 acre tract of land located 11 miles from the UM campus in Oxford, Mississippi. EM responses were surveyed along transects and randomly chosen locations using a Geonics EM38. The apparent electrical conductivity (EC) of the soil was determined in both a vertical and horizontal dipole position, which correspond to deep (~1m) and shallow (~0.5) measurements, respectively. We find that EC is primarily controlled by soil physical and chemical properties under moderately dry conditions. Under wetter conditions, EC shows good correlation with soil moisture content. EC variograms show similar spatial structures at different times. However, EC variability increases under wet conditions. These results imply that pore surface conduction dominates under dry conditions, while pore water conduction becomes more important under wet conditions. Variogram similarity suggests that spatial variations in EC are strongly influenced by spatial variations in soil properties regardless of soil moisture conditions. These relationships may allow the development of a predictive model for soil moisture based on EC measurements in North Mississippi loamy soils.