Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/2/2006
Publication Date: 8/3/2006
Citation: Grigera, M.S., Drijber, R.A., Eskridge, K.M., Wienhold, B.J. 2006. Soil microbial biomass relationships with organic matter fractions in a nebraska corn field mapped using apparent electrical conductivity. Soil Science Society of America Journal 70:1480-1488. Interpretive Summary: 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- to 90-cm) that showed higher correlations with vertical ECa included total C (r = 0.87), clay (r = 0.83), total dissolved solids (r = 0.68) and depth of topsoil (r = 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 = 0.85) and actinomycetes (r = 0.71) biomarker concentrations were more highly correlated with fine particulate organic matter (POM) than coarse POM (bacteria r = 0.69 and actinomycetes r = 0.48). In contrast, fungal (r = 0.77) and mycorrhizal (r = 0.48) biomarker concentrations were only correlated 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.
Technical Abstract: Soils vary within a field and this variation effects crop yield, crop residue decomposition, and nutrient and water availability. Variation in soil depth, and amounts of sand, silt, and clay do not change quickly with time and spatial patterns within a field in these properties are stable. These stable properties influence the accumulation of soil organic matter and the activity of soil microorganisms but this interaction is not well understood. A study was conducted in an irrigated corn field in central Nebraska to determine the relationship between soil microorganism and soil organic matter among sites within a field that differed in stable soil properties. The field was divided into four zones that differed in organic matter, clay content, depth of soil, and dissolved salts. Bacteria and actinomycetes were most strongly associated with very small soil organic matter particles while fungi were associated with larger soil organic matter particles. A better understanding of how soil microorganisms vary within a field and how processes facilitated by soil microorganism, such as residue decomposition and nutrient availability, will result in better management of spatially variable fields.