Effects of Organic Amendments On Aggregation and Microbial Community Dynamics in Soils.

This project evaluates effects of soil amendments on aggregate formation, microbial residue accumulation, and microbial community dynamics in three different soils. The native soil structure of experimental soils was destroyed by forcing soils through a 250µm sieve. Soils were treated with organic amendments based on amendment C content at a rate of 0.01g-amendment C/g soil. Amendment treatments included hairy vetch residue, dairy manure, compost, or no-amendment. Soils were then incubated at 25°C for 80 days. Soils were destructively sampled on incubation days 0, 5, 12, 30, and 82. These samples were analyzed for water stable aggregation in four aggregate size classes using a wet sieving method.

Following sieving, incubated soils were analyzed for accumulation of the amino sugars glucosamine and muramic acid. These amino sugars are microbial residues that can be used to characterize the relative contributions of fungi and bacteria to aggregation processes. Changes in microbial community structure were assessed through analysis of microbial fatty acids.  Relationships between amendment type, soil type, microbial parameters, and aggregate formation through time were investigated. The hypothesis being tested is that, relative to other amendments, amendments that stimulate greater fungal activity will also promote greater macroaggregate formation. Anticipated outcomes of this work will provide information on soil management practices that stimulate soil structural enhancement by promoting a favorable microbial community. This information would be useful to those interested in maximizing the agronomic benefits associated with building and sustaining good soil structure.