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 (SOM) and soil fauna in the Ultisols of the Horseshoe Bend (HSB) agroecosystem site in Georgia have been studied in replicated experimental plots since 1978. The experimental treatments (no-tillage (NT) and conventional-tillage (CT) regimes) are continuing to diverge in amounts and distribution of SOM. Our research has focused on long-term measurements of the gradually-increasing base of soil organic matter from C3-pathway plants, in winter cover-crop and summer crop rotations that have been in effect since 1997. We have found greater amounts of new C in all aggregate size fractions in NT compared to CT in the shallow soil; slightly 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. However, although preliminary, these data also suggest that aggregates in NT may be storing larger amounts of new C than aggregates in CT.