Using Electromagnetic Induction to Identify Subsurface Variation of Soil Properties Associated with Gilgai.

Subsurface soil properties associated with Vertisol gilgai are known to vary in clay, carbonate, and organic matter content.  All three soil properties are known to affect soil shrink-swell potential and subsequently, the extent of surface soil cracking.  To be able to model soil cracking dynamics and the associated impacts on landscape hydrology, a method that maps subsurface soil variability associated with gilgai is needed. The EM38 non invasively measures ECa, which is influenced by soil water content, clay content, depth to parent material, salinity, temperature and inorganic carbon content.   Bulk electrical conductivity (ECa) has been shown to map spatial variability in soil clay content, water holding capacity, and depth to parent material at the field scale.  The EM38 has an effective spatial sensing area of approximately 1 m², which may be fine enough to sense soil properties of microhighs and microlows independently.  We investigated the ability of the EM38 to map subsoil variability associated with gilgai formation.  Surveys were conducted on a gilgai forming Houston Black (Udic Haplusterts) at two locations, one location where gilgai were well developed and undisturbed and another location where the field had been plowed approximately 20 years prior and had weakly reformed microtopography.   After the surveys, soil cores were collected to 1.5 meters within 48 hours of the EMI survey and analyzed for volumetric water content, depth to parent material, inorganic carbon content (carbonate), and clay content.  Preliminary results indicate an EMI response in the field with well developed gilgai and little to no response in the disturbed field. In the undisturbed field, higher ECa values occur in microlows compared to microhighs.