Characterizing spatial variability is an important consideration of any landscape scale soil related problem. Apparent soil electrical conductivity (ECa) is a quick, reliable measurement that is frequently used for the spatial characterization of edaphic properties. It is the objective of this paper (i) to provide protocols for conducting an ECa survey and (ii) to apply these protocols to a soil quality assessment in California's San Joaquin Valley (SJV). The protocols are comprised of eight general steps. The soil quality assessment was conducted on a 32.4-ha field where a mobile electromagnetic induction (EM) survey was performed following outlined protocols. The EM survey consisted of ECa measurements taken at 22,177 locations in April 2002. A response-surface sampling design identified 40 sites where soil-core samples were taken at 0.3-m increments to a depth of 1.2 m. Soil samples were analyzed for a variety of physical and chemical properties associated with soil quality for an arid-zone soil. Analysis characterized the soil as montmorillonitic, saline, and sodic with ECe (electrical conductivity of the saturation extract) varying from 4.83 to 45.3 dS m-1, SAR (sodium adsorption ratio) from 5.62 to 103.12, and clay content from 2.5% to 48.3%. Spatial trends showed high areas of salinity and SAR in the center of the southern half of the study area. Maps of spatial variation of properties associated with soil quality for an arid-zone soil (i.e., ECe, SAR, B, and Mo) are presented. The developed protocols provide the guidelines to assure reliability, consistency, and compatibility of ECa survey measurements and their interpretation.
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