Effects of the Quality of Organic Soil Amendments on the Soil Community and on Nitrogen Mineralization in an Agroecosystem in the Georgia Piedmont

2006 Annual Report for GS05-044

Project Type: Graduate Student
Funds awarded in 2005: $8,576.00
Projected End Date: 12/31/2007
Grant Recipient: University of Georgia
Region: Southern
State: Georgia
Graduate Student:
Major Professor:
Carl Jordan
University of Georgia

Effects of the Quality of Organic Soil Amendments on the Soil Community and on Nitrogen Mineralization in an Agroecosystem in the Georgia Piedmont


There was wide variation in the biochemical composition of substrates in regards to all quality parameters. For the first three weeks of decomposition the substrates with faster mineralization were amorpha and clover followed by the mixture, rye and pine and hay. Rates were lower in later stages but followed the same pattern. PCA of PLFA data indicated differentiation of microbial communities under different substrates associated with differences in Gram + bacteria, fungi and actinomycetes. Substrate did not have an effect on total nematode abundance. Bacterial feeding nematodes responded to substrates after three months but not after six months. Substrate did not have an effect on microarthorpod abundances.

Objectives/Performance Targets

1. Determine biochemical properties and mineral nitrogen release patterns of the following amendments over a growing season: (a) green manure from a leguminous alley cropping species (Amorpha fruticosa L., a native woody shrub), (b) green manure from a legume species (crimson clover) used as winter cover crop, (c) green manure from cereal rye used as winter cover crop, (d) chicken manure and wood chips compost and (e) hay, (f ) pine needles used as mulch.
2. Assess the response of the microbial community, nematodes and microarthropods to the above mentioned substrates in soils with contrasting levels of organic matter (in adjacent fallow and cultivated plots).
3. Using experimental and modeled data, study the effect of the observed responses of the soil community on N release into the soil.
4. Assess the suitability of amendments in providing N to the plant during the growing season, by comparing estimated and modeled nitrogen release patterns under different amendment quality/soil community scenarios to crop plant N demand curves.


Accomplished work:

-Biochemical quality of substrates: % Carbon, % Nitrogen, % Phosphorus, % Cellulose, % Hemicellullose and % Lignin were determined for all plant substrates. Data has been processed and analyzed.
-N mineralization after surface application of five plant materials and their mixture was measured by incubation of cation and anion exchange resins. Incubation lasted six months starting in July. Data had been processed and analyzed.
-N mineralization of compost and one plant substrate (leaves of Amorpha fruticosa) was measured in the low organic matter soil (main plots were plant substrates were incubated) and high organic matter soil (in adjacent forested area). Data not analyzed yet.
-Soil microbial biomass in soil under different substrates was estimated with Chloroform Fumigation Extractions. The response of the microbial community was assessed using Phospholipid Fatty Acids profiles and markers for main microbial groups. Data processed and analyzed.
-The abundance of nematodes and their distribution in feeding groups was evaluated under different substrates. Microarthropods (Acarids and Collembola) abundances were monitored under different substrates. Data has been processed and analyzed.

Work left to do:

-Use food web model to study the effect of the change in soil communities due to different substrates on N concentration in soil
– Estimation of N demands of winter squash, cowpeas, basil and sunflower
-Comparison of estimated and modeled nitrogen availability patters to crop N demand curves for the above mentioned crops

Impacts and Contributions/Outcomes

The results of ongoing research will be useful in informing the selection of organic amendments in vegetable systems in the piedmont region. This project will develop general management recommendations to enhance the role of soil biota in providing nitrogen to the plants. Recommendations will be directly delivered to the Full Moon Cooperative Farm growers in Athens, GA and through them, to the network of organic producers in the area.


Yolima Carrillo

Graduate Student
Institute of Ecology, University of Georgia
Ecology Building
Athens, GA 30602
Office Phone: 7062541250