Long-term consequences of biochemical and biogeochemical changes in the Horseshoe Bend LTREB agroecosystem, Athens, GA.
Coleman, David*,1, Hunter, Mark2, Hendrix, Paul1, Crossley, Deryee1, Arce-Flores, Sofia1, Simmons, Breana1, Wickings, Kyle, 1 University of Georgia, Athens, GA2 University of Michigan, Ann Arbor, MI
ABSTRACT- Understanding many soil processes, including the accumulation of organic matter and the formation of soil aggregates, requires research that is conducted over several decades. The dynamics of soil organic matter (SOM) and biota in the Ultisols of the Horseshoe Bend (HSB) agroecosystem site in Georgia have been studied in replicated experimental plots since 1978. Ben Stinner helped design and participated in the initial studies. The experimental treatments (no-tillage (NT) and conventional-tillage (CT) regimes) are continuing to diverge in amounts and distribution of SOM. Winter cover crops continue to influence SOM, with crimson clover subplots having 40 to 50 g.m-2 more than in wheat subplots. Since 1998, using delta 13C, we have followed the gradually-increasing base of soil organic matter from C3-pathway plants in winter cover-crop and summer crop rotations (kenaf and cotton). We found greater amounts of new C in all aggregate size fractions in NT compared to CT in the shallow soil; somewhat higher values occurred in CT in deeper soils. It is likely that new organic matter is being mineralized faster in CT than in NT soils. Aggregates in NT are storing ca. 30 to 40% more new C than aggregates in CT. We have also measured long-term non-target effects of the Bt Cry1AC protein on soil biota, comparing plots with Bt and non-Bt cotton. Some marked differences in above- and below-ground biota were measured, possibly due to differences in available nitrogen in Bt vs. non-Bt cotton.
Key words: agroecosystems, aggregates and organic matter, Bt cotton
All materials copyright The Ecological Society of America (ESA), and may not be used without written permission.