The preservation of soil organic C is crucial because of its role in improving soil aggregation, soil fertility, and overall soil quality. Tillage and harvest management regimes can influence SOC, but long-term, continuous experiments are rare. We investigated the effects of tillage and residue application on SOC dynamics, turnover of relic forest-derived C and cycling of new C4 (corn)-derived C in water stable aggregates after 31 yr of continuous management at the University of Connecticut. The plots have been under no-till (NT) or conventional till (CT) management, with residues returned (+) or removed (-) annually within each tillage treatment. In soils from our long-term experiment, strong treatment-induced patterns are seen in the >2000-um macroaggregates, with NT and residue inputs significantly increasing SOC content and aggregate distribution. However, NT management did not increase SOC or aggregate distribution in the other aggregate size classes. Soils at our site have a relatively high organic C content and a high concentration of Fe+2 and illite clay possibly leading to strong clay particle-polyvalent metal-organic matter bonds that protect organic materials from microbial decomposition and increase aggregate stability. It is possible that the combination of soil mineralogy, organic matter, and time has contributed to the buildup of SOC in soil aggregates in our system.
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