Comparing water-stable aggregate distributions, organic matter fractions and carbon turnover using 13C natural abundance in conventional and no tillage soils
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Water-stable aggregates (WSA) physically protect soil organic matter (SOM) from decomposition, resulting in SOM pools with longer turnover times. Intensive cultivation disrupts soil aggregates, whereas conservation management practices increase aggregate stability and carbon concentration in the soil. Soil samples were taken from No-tillage (NT) and Conventional-tillage (CT) plots at Horseshoe Bend field site in Athens, Georgia. Soil cores were divided in depths and wet sieved into aggregates >2000, 250-2000, 53-250, and <53 µm. I determined aggregate distribution, total carbon (C) and nitrogen (N), mineral and particulate 13organic matter (POM) associated C and N, and used C natural abundance to trace recent organic inputs and C turnover in the soil. These results support the conceptual model of aggregate turnover; the net input rate increased with aggregate size fractions, indicating a slower turnover for microaggregates than macroaggregates and suggesting physical protection of old C in the smaller aggregate fraction.