Characterizing and Mapping the Field Scale Spatial Variability of Surface Horizon Soil Properties and Water Content with Noninvasive EM38.

The spatial variability of soil physical properties at the field scale is increasingly important in agriculture and natural resource management. Changes in topography, parent material, management practices, erosion/deposition rates, etc. at a field scale can influence the variability of the soil’s physical properties and direct management and land use plans.  Understanding and quantifying this spatial variability quickly and efficiently is crucial to create high-resolution soil property maps to help guide precision management. The Geonics EM38 is a noninvasive geophysical sensor which is used to measure the apparent electrical conductivity (EC_a) of the soil through electromagnetic induction – primarily influenced by soil texture (clay content), soil moisture content, and salinity.  Soil moisture has been found to be a significant contributor to EC_a, making EM38 potentially useful in measuring both spatial and temporal variation in available soil water content across a landscape. This study conducted at the Lake Wheeler Road Field Laboratory in Raleigh, North Carolina, during the summer of 2015 combined lab analysis of soil physical properties and EM38 surveys to examine the ability of EM38 to quantify and map soils based upon their physical properties and soil moisture (0-0.15m) in the root zone.  Analyses of soil cores collected at 14 discrete locations included the determination of soil particle size distribution, bulk density, and soil water retention. Multiple EM38 surveys were conducted along transects of a rain-fed agricultural field and used to calibrate readings with volumetric water content. Data and maps will be presented of EC_a survey measurements, water retention curves, particle size analyses, and available water content maps. The objectives of this study were to determine the ability of the EM38 sensor to measure and map the spatial variability of soil physical properties in coarse textured/gravelly Piedmont soils and calibrate/test the sensors ability to measure root-zone moisture conditions.