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Soils exhibit spatial variability in their properties. One approach for delineating field-scale variability involves mapping the variation in apparent soil electrical conductivity (ECa). The objectives of this study were to evaluate the physical and chemical soil characteristics that define ECa classification and the association of specific soil microbiological communities with these soil properties. In May 2003, ECa was measured in a field in Buffalo County, Nebraska, and processed to create four ECa zones based on ranges of horizontal and vertical ECa measurements using unsupervised classification. Soil properties (0-90 cm) that showed higher correlations with vertical ECa included total C (r 5 0.87), clay (r 5 0.83), total dissolved solids (r 5 0.68), and depth of topsoil (r 5 0.70). These properties influence soil water availability in this field. Soil microbial groups were correlated with different soil C fractions in the 0-to 15-cm depth and were similar across ECa zones. Bacterial (r 5 0.85) and actinomycetes (r 5 0.71) biomarker concentrations were more highly correlated with fine particulate organic matter (POM) than coarse POM (bacteria r 5 0.69 and actinomycetes r 5 0.48). In contrast, fungal (r 5 0.77) and mycorrhizal (r 5 0.48) biomarker concentrations were correlated only with coarse POM. Given current knowledge of the spatial distribution of POM and aggregates, we hypothesize that microorganisms are also spatially distributed and that fungal groups are closely associated with coarse POM early in the growing season.

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