Soil Structural Units Identified with Electrical Resistivity Tomography and Varying Flow Rates.

One of Dr. Ray Allmaras' strong research interests was soil structure. Ray's engaging mentoring style together with his vast research experience were invaluable assets that helped me defining my own interests in the subject. Electrical resistivity tomography (ERT) has been used to image the transport of solute through undisturbed soil columns. The objective of this works was to use ERT and geostatistical methods to define regions within a soil column with similar responses to water flow. An undisturbed soil column 0.3 m in diameter and 0.5 m long was sampled from a forested area and encased in a PVC tube. In the laboratory, 104 stainless steel electrodes arranged in 8 horizontal planes were installed through the PVC wall and into the soil. Water was applied to the top of the soil column with a mist infiltrometer at 5 flow rates of increasing magnitude. After achieving steady state, ERT measurements were collected and inverted to produce 62,208 values of electrical resistivity for each flow rate. The ERT datasets were analyzed with a local indicator of spatial association (LISA) method to identify clusters of low and high values of electrical resistivity representing wet and dry regions in the soil, respectively. The spatial distributions of regions of relatively uniform electrical resistivity will be discussed.