| Abstrakt: |
Soil C sequestration research has historically focused on the top 0 to 30 cm of the soil profile, ignoring deeper portions that might also respond to management. In this study we sampled soils along a 10‐treatment management intensity gradient to a 1‐m depth to test the hypothesis that C gains in surface soils are offset by losses lower in the profile. Treatments included four annual cropping systems in a corn (Zea mays)‐soybean (Glycine max)‐ wheat (Triticum aestivum) rotation, perennial alfalfa (Medicago sativa) and poplar (Populusx euramericana), and four unmanaged successional systems. The annual grain systems included conventionally tilled, no‐tillage, reduced‐input, and organic systems. Unmanaged treatments included a 12‐yr‐old early successional community, two 50‐yr‐old mid‐successional communities, and a mature forest never cleared for agriculture. All treatments were replicated three to six times and all cropping systems were 12 yr post‐establishment when sampled. Surface soil C concentrations and total C pools were significantly greater under no‐till, organic, early successional, never‐tilled mid‐successional, and deciduous forest systems than in the conventionally managed cropping system (p≤ 0.05, n= 3–6 replicate sites). We found no consistent differences in soil C at depth, despite intensive sampling (30–60 deep soil cores per treatment). Carbon concentrations in the B/Bt and Bt2/C horizons were lower and two and three times more variable, respectively, than in surface soils. We found no evidence for C gains in the surface soils of no‐till and other treatments to be either offset or magnified by carbon change at depth. |
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