Apparent electrical conductivity response to spatially variable vertisol properties

Abstract

Though much has been done to understand proximally-sensed bulk apparent electrical conductivity (ECa) in agricultural soils, many of the soil properties identified to be mappable using these techniques, such as salinity and clay content, are not expected to drive ECa response in a non-saline Vertisol. In Vertisols, agrillipedoturbation creates meter-scale variability in soil moisture and chemical properties associated with gilgai features, and if developed from calcareous parent material, can exhibit meter and landscape scale variability in inorganic C content. The ability to map inorganic C may be especially useful in a Vertisol due to its strong correlation with shrink-swell potential. The overall goal of this project was to investigate the potential for mapping inorganic C using ECa surveys in a calcareous Vertisol, with the future goal of mapping shrink-swell potential on these landscapes. On a 40- by 50-m field with intact circular gilgai, ECa was mapped under both moist and dry soil conditions. Soil samples were taken for water content, clay content, inorganic C content, salinity, and depth to parent material. Under moist soil conditions, the strongest correlation to ECa was inorganic C content (r=−0.63), followed by water content (r=0.49); however, under dry conditions, only inorganic C content was significant (r=−0.60). In addition, ECa surveys and inorganic C samples were taken for two larger watersheds of 10 and 14ha. Again, inorganic C content was significantly and reliably correlated to ECa for both fields, and the resulting regression slopes and intercepts were not significantly different between watersheds, though the surveys were conducted at different times. Results suggest that ECa can be used to map inorganic C content in Vertisols weathered from calcareous parent materials, allowing for spatial inference of shrink-swell potential which may be useful in distributed hydrology modeling.