Investigation of Electrical Conductivity As Measured by Electromagnetic Induction As a Means to Map Shrink-Swell Potential In Vertisols.

Modeling water flow in Vertic landscapes is complicated by spatial and temporal differences in surface cracking.  Hydrologic properties of Vertisols are strongly influenced by the presence of surface cracks, which allow water to bypass the soil matrix and directly enter the subsoil.  To model water flow on these landscapes, information on the spatial distribution and magnitude of soil cracking is needed.  The overall objective of this study was to find means to map the shrink-swell (cracking) potential of soil across Vertic landscapes with the goal of improving simulations of infiltration and runoff.  High shrink-swell potential of soil is generally related to high clay content and high specific surface area of the clay.  Soils with high calcium carbonate content generally have lower shrink-swell potential than non-calcareous clay soils.  Because clay content, surface area of the clay, and calcium carbonate content of soil influence bulk soil electrical conductivity (ECa), we explored mapping shrink-swell potential using field-based measurements of ECa with electromagnetic induction (EMI).  EMI surveys of ECa were conducted in fields of Houston Black (Udic Haplustert) and Burleson (Udic Haplustert) Vertisols in Texas.  Soil cores were collected for laboratory measurements of shrink-swell potential, clay content, clay surface area, calcium carbonate content, and electrical conductivity of the soil at selected locations within the surveys which were chosen by stratifying ECa values. Results of the efforts to map shrink-swell potential of soil with EMI measures of ECa will be presented.