Soil-carbon results can reverse when you sample below the surface
WHAT THE EVIDENCE SAYS
Archived soils from two Nebraska crop-residue experiments and a Great Lakes corn-switchgrass trial showed carbon change varied by depth and fraction. Residue retention in the 19-year Nebraska trial increased surface carbon; switchgrass showed profile-wide carbon loss at the Great Lakes site. Permanganate-oxidizable carbon followed total-carbon trends better than several other fractions.
WHY IT MATTERS / OUR READ
For working lands, choose a clear baseline and repeatable sampling depth before treating shallow carbon change as success. Compare profiles, record vegetation and residue histories, and evaluate multiple carbon indicators.
CAVEATS / UNCERTAINTY
Only three trials and specific management histories; results cannot establish that switchgrass generally depletes carbon or that any one fraction certifies credits.
SOURCE
Biogeochemistry — Naasko et al. (2026)
View original evidence ↗
Midwest long-term experiments argue for depth-aware stewardship and monitoring.
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