LTREB: Long-term Consequences of Biochemical and Biogeochemical Changes in the Horseshoe Bend Agroecosystem, Athens, GA.

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0214946ColemanUnderstanding many soil processes, including the accumulation of organic matter andthe formation of soil aggregates, requires research that is conducted over decadal timeperiods. The dynamics of soil organic matter and soil fauna at the Horseshoe Bend(HSB) agroecosystem site in Georgia have been studied in replicated experimentalplots since 1978. Analyses indicate that the experimental treatments (no-tillage andconventional-tillage regimes) are continuing to diverge. It is essential to continue theexperiments for an additional six years, to enable prediction of what the long-termconsequences of our manipulations will be. Consequently, a continuation of ongoingLTREB research on soil processes in no-till and conventional till plots at HSB is proposed, withsome significant changes. The new research focuses on two related areas:1) long-term measurements of the gradually-increasing base of soil organic matter fromC3-pathway plants, in crop rotations that have been in effect since 1997.2) following the production, accumulation, fate and ecological effects of the Bt proteinsfrom the summer planting of Bt (and non-Bt) cotton in subplots within our main plots.The relationship between these focal areas is simple. The variation in the size of soilaggregates may influence the sequestration of Bt toxins, and their breakdown products,within soils. It has already been shown that no-tillage management systems at HSBgenerate an increasing representation of soil macroaggregates in comparison to themarkedly reduced macroaggregates in our conventional tillage plots. Therefore, it ishypothesized that no-tillage systems will sequester more Bt-related products than willconventional-tillage plots.Several short-term studies (see references in Project Description) have failed to detectdeleterious changes in non-target soil fauna as a result of Bt in crop residues. Thereare three possible explanations for this: a) that no deleterious effects exist, b) that short-term experiments do not adequately predict the long-term consequences of repeatedexposure to Bt residues, and c) that effects are contingent upon properties of the soilsuch as aggregate size. It would seem prudent to be able to distinguish among thesepossibilities and the long-term plantings at HSB will allow that to occur.