Cover Crop and Fertilizer Effects on Soil Bacterial Community Structure and Function in Organic Farming Systems.

We investigated the effects of cover crops and organic-approved fertilizers on soil bacterial community structure and function. A field experiment was established in spring 2012 at four southern Minnesota locations. Organic amendment treatments were applied to field plots in fall 2012 following barley (Hordeum vulgare). Treatments were winter rye (Secale cereale), hairy vetch (Vicia villosa), buckwheat (Fagopyrum esculentum), oilseed radish (Raphanus sativus), beef manure, pelleted chicken manure, Sustane 8-2-4, and a no-amendment control. The study fields were planted to corn (Zea mays) in spring 2013. Field soil samples were collected before and after treatment, and rhizosphere soil samples were collected from the corn crop. Soil respiration, N mineralization, and nutrient levels were measured in post-treatment samples. Enzyme activity potential of phosphatase, N-acetyl-β-D-glucosaminidase, and β-glucosidase were measured using fluorometric assays.  Bacterial community structure was determined using Illumina sequencing of the V5-V6 hypervariable region of bacterial 16S rDNA . Preliminary analysis found an average of 2601 Operational Taxonomic Units (OTUs) per sample, with a core group of 422 OTUs present in all samples.  Differences in bacterial community structure were associated with amendment treatment. Soil respiration was affected by amendments; the largest effect was with pelleted poultry manure, which increased respiration by 232% compared to the no-amendment control. Correlations among soil function metrics and bacterial community structure parameters will be presented to show whether inferences about community function can be made on the basis of phylogenetic data within the context of organically managed agricultural soils.