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

2009 Annual Report for GS08-065

Project Type: Graduate Student
Funds awarded in 2008: $10,000.00
Projected End Date: 12/31/2011
Grant Recipient: University of Kentucky
Region: Southern
State: Kentucky
Graduate Student:
Major Professor:
Elisa D'Angelo
University of Kentucky
Major Professor:
Mark Williams
University of Kentucky

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.

Collaborators:

Shawn Lucas

shawn.lucas@uky.edu
PhD. Student
University of Kentucky, Plant and Soil Sciences
105 Plant Science Building
1405 Veterans Drive
Lexington, KY 40546-0312
Office Phone: 8592575020
Mark Williams

mark.williams@uky.edu
Associate Professor
University of Kentucky, Dept. of Horticulture
N-318 Agricultural Sciences North
Lexington, KY 40546-0091
Office Phone: 8592572638
Elisa D’Angelo

edangelo@uky.edu
Associate Professor, Soil & Water Biogeochemistry
University of Kentucky; Plant and Soil Sciences
105 Plant Science Building
1405 Veterans Drive
Lexington, KY 40546-0312
Office Phone: 8592578651