Long-Term Management Practices Influenced Soil Aggregation and Carbon Dynamics.

Soil aggregation protects soil organic C (SOC) against rapid decomposition, improves soil quality, and reduces soil erosion potential.  The objectives of this study are to evaluate the effects of long-term (21 yrs.) management practices on SOC, water stable aggregate (WSA), and aggregate-associated C. A study was initiated in 1999 on a moderately well-drained Kennebec silt loam (Fine-silty, mixed, superactive, mesic Cumulic Hapludoll) with continuous corn (Zea mays L.), manure (M) and NH₄NO₃ fertilizer (F) as the N sources, and no-tillage (NT) and conventional tillage (CT) practices. Soils were incubated for 328 d, sampled in 1999, and 56 d, sampled in 2012, at 35^oC at water potential of -0.033 MPa.  Periodically, throughout the incubation, soil cores were separated into four aggregate-size classes (> 2000, 250-2000, 53-250, and 20-53 μm) by wet sieving. At the end of the incubation, SOC, at 0- to 5-cm depth, was greatly retained with NT and M treatments. In addition, the prolonged existence of macroaggregates (> 2000 μm) and macroaggregate-associated C were maintained by NT and M treatments.  Twenty one years of NT and M practices, show that the longevity of macroaggregates is progressing to achieve the natural ecosystem conditions.  Over all, under favorable mineralization conditions, the longevity of soil aggregates, aggregate-associated C, and thus C conservation were more likely sustained by NT, M, and the combination of NT and M management.