Spatial Variability of Electrical Conductivity and Its Relationship to Soil Properties at The University of Mississippi Soil Moisture Observatory

The Soil Moisture Observatory (SMO) at the University of Mississippi (UM) is a 5 acre tract of a former agricultural field at the UM Biological Field Station. Preliminary investigations of this site included 60 continuous soil cores using the Geoprobe sampling technique. These soil cores were taken to a depth of 1.5 meters to correspond to the approximate depth of penetration for a Geonics EM38. The Geonics EM38 uses electromagnetic induction to measure apparent electrical conductivity (ECa) of the soil. Weekly readings using the EM38 were conducted at the 60 sites. Soil samples were collected on the fourth week of EM38 readings. These samples were analyzed for particle size distribution, porosity, bulk density, iron content, and volumetric moisture content. This analysis determined that soil physical and chemical properties control the spatial variations in ECa. Volumetric moisture content shows correlation lengths less than 25m at shallow depths and greater than 35m deeper; variability also increases with depth. Volumetric moisture content appears to be most closely related to soil particle size. The temporal variations of the variograms of ECa indicate a complex relationship between soil properties and ECa.