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

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

Summary

Nitrogen availability is an important factor in limiting yields especially in low-input and organic systems. In these systems, soil organic amendments –as opposed to chemical fertilizers- are intended to play a major role in providing nutrients to crops. Whenever the use of inorganic nitrogen is being replaced by organic materials, the availability of N in soil depends increasingly on biological processes of nutrient release. This, in turn, requires increased reliance on the biochemical quality of the organic additions and on the functioning of the soil organisms. This project seeks to study how the quality of organic amendments and the structure of the soil community interact to determine N availability for plants. The efficacy of a number of commonly used and experimental in-situ generated organic amendments in increasing nitrogen availability, and their effects on the structure of the soil community will be assessed. Experimental and modeling approaches will be used to study interactive effects.
The outcomes of this project will be useful in informing the selection of organic amendments in vegetable systems to improve synchrony of N release and demand. From the analyses of empirical and experimental data, we will be able to develop general management recommendations to enhance soil biota’s role in nitrogen release. In addition, this project will improve our ecological understanding of the impact of organic amending on the role that the soil community plays in nutrient cycling in agroecosystems.

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 (red clover) used as winter cover crop, (c) green manure from rye used as winter cover crop, (d) municipal yard waste compost and (e) hay.
2. Assess the response of the population of soil bacteria, fungi, protozoa, 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.

Accomplishments/Milestones

As stated in the proposal the execution of this project began only until March of 2006. In 2005 only preparation work was carried out. To date, the organic amendments to be used in the experiment have been selected and analyzed for biochemical quality. The experimental plots have been selected and are being prepared for the application of amendments in May of 2006. Nitrogen release, soil populations and plant biomass will be measured between May and October. Plant material, soil biota and soil fatty acids will be processed and analyzed between October 2006 and February 2007. Data analysis and modeling work will be carried out between February and July of 2007.

Impacts and Contributions/Outcomes

The results of the proposed 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. Recomendations 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.

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