Effects of organic amendments on aggregation and microbial community dynamics in soils

Effects of organic amendments on aggregation and microbial community dynamics in soils

Summary

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 0.250mm 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 vetch, farmyard manure, OMRI certified compost, or no-amendment. Soils were then incubated at 25C for 80 days. Soils were destructively sampled on incubation days 0, 5, 12, 30, and 80. These samples were analyzed for macroaggregate formation using a wet sieving method.

Following sieving, incubated soils will be 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 will be assessed through analysis of microbial fatty acids. Relationships between amendment type, soil type, microbial parameters, and aggregate formation through time will be 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.

Objectives/Performance Targets

1. Observe accumulation of microbial residues (glucosamine derived from fungi and muramic acid derived from bacteria) and measures of microbial community structure (ester-linked fatty acid methyl esters) in small macroaggregates formed in soils receiving different organic inputs.

2. Determine the influence of organic inputs on aggregate formation and aggregate stability in three different soils.

3. Examine relationships between microbial residues, microbial community structure, and aggregate dynamics relative to organic inputs.

Accomplishments/Milestones

This research is currently ongoing. Preliminary studies showed that measuring the percentages of water stable aggregates in several size classes, using the wet sieving method of Elliot (1986), is better suited for observing short-term amendment related soil structure changes than the dry sieving method of Diaz-Zorita et al. (2007). At the time of this report submission, samples have been incubating for 65 days. Analysis of soil aggregation has been performed for samples removed from the incubator on days 0, 5, 12 and 30. Statistical analysis of soil aggregation data is currently ongoing. In addition, we are currently conducting analysis of soil microbial community structure in incubated soils using fatty acid methyl ester (FAME) profiles. Soil amino sugar analysis will commence when FAME analysis is completed. Soils waiting to be analyzed for microbial parameters have been stored at -20C.

Impacts and Contributions/Outcomes

Outcomes of this study will be useful to researchers and producers interested in maximizing the agronomic benefits associated with building and maintaining good soil structure. Understanding which soil management practices stimulate structural enhancement by promoting a favorable microbial community would be useful in developing soil amendment plans on farms. As this research is ongoing, specific outcomes of this research have yet to be fully determined.

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