Data from: Soil carbon maintained by perennial grasslands over 30 years but lost in field crop systems in a temperate Mollisol

To mitigate climate change, some seek to store carbon from the atmosphere
in agricultural soils. However, our understanding about how agriculture
affects soil organic carbon is muddied by studies (1) lacking longitudinal
data, (2) ignoring bulk density changes, or (3) sampling only surface
soils. To better understand soil organic carbon trends, here we measured
changes over 30 years in density-corrected, full-soil-depth (90 cm) soil
organic carbon stocks under 6 cropping systems and a restored prairie in a
Mollisol of southern Wisconsin, USA. Cash-grain systems and alfalfa-based
systems lost soil organic carbon. Prairie and rotationally-grazed pasture
maintained soil organic carbon. Average soil organic carbon losses for
cash-grain and alfalfa-based systems were −0.82 (±0.12) and −0.64 (±0.17)
Mg C ha-1 yr-1, respectively. Sensitivity analysis showed that incomplete
methodologies overestimated soil organic carbon improvements. Our findings
using more comprehensive methods demonstrate the inadequacy of row-crop
systems and the need for well-managed grasslands to protect soil organic
carbon in productive agricultural soils of the Upper Midwest USA.