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

University Of Georgia Research Foundation Inc, Athens GA

Investigators

Abstract

0214946 Coleman Understanding many soil processes, including the accumulation of organic matter and the formation of soil aggregates, requires research that is conducted over decadal time periods. The dynamics of soil organic matter and soil fauna at the Horseshoe Bend (HSB) agroecosystem site in Georgia have been studied in replicated experimental plots since 1978. Analyses indicate that the experimental treatments (no-tillage and conventional-tillage regimes) are continuing to diverge. It is essential to continue the experiments for an additional six years, to enable prediction of what the long-term consequences of our manipulations will be. Consequently, a continuation of ongoing LTREB research on soil processes in no-till and conventional till plots at HSB is proposed, with some significant changes. The new research focuses on two related areas: 1) long-term measurements of the gradually-increasing base of soil organic matter from C3-pathway plants, in crop rotations that have been in effect since 1997. 2) following the production, accumulation, fate and ecological effects of the Bt proteins from 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 soil aggregates may influence the sequestration of Bt toxins, and their breakdown products, within soils. It has already been shown that no-tillage management systems at HSB generate an increasing representation of soil macroaggregates in comparison to the markedly reduced macroaggregates in our conventional tillage plots. Therefore, it is hypothesized that no-tillage systems will sequester more Bt-related products than will conventional-tillage plots. Several short-term studies (see references in Project Description) have failed to detect deleterious changes in non-target soil fauna as a result of Bt in crop residues. There are 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 repeated exposure to Bt residues, and c) that effects are contingent upon properties of the soil such as aggregate size. It would seem prudent to be able to distinguish among these possibilities and the long-term plantings at HSB will allow that to occur.