Land-use effects on soil carbon and nitrogen on a U.S. midwestern floodplain

Wet prairie soils in the Midwest store significant amounts of soil organic carbon(SOC) and total nitrogen(TN). Crop fields, prairie restorations of varying ages, and remnant prairies on a floodplain soil(Fine-silty, mixed, superactive, mesicTypic Endoaquolls) in southern Wisconsin were intensively sampled to estimate changes in SOC and TN due to the conversion of native prairie to row crops and the restoration of prairie on cropped land. In the top 10 cm of soil, remnant prairies contained an additional 24 Mg SOC ha ^-1 and 1.7 MgTN ha ^-1, compared with currently cropped fields(P ≤ 0.05). In the top 25 cm, remnant prairies contained an additional 2.4 MgTN ha ^-1 compared with currently cropped fields(P ≤ 0.05), but a difference was not detected in SOC between unplowed remnants and cropped fields. Soil inorganic carbon(SIC) was significantly greater at all depths in cropped fields than in unplowed remnants. No differences in SOC and TN mass between annually tilled(AT) and biennially tilled(BT) fields were detected, except for greater TN in the top 10 cm of BT fields. No differences between currently cropped fields and prairie restorations less than 7 yr old were detected, however a 7- and 45-yr-old restoration had greater SOC and TN mass than crop averages. These results suggest that the loss of SOC in the A horizon of the soils on this floodplain through agriculture has likely been small. Additionally, the redistribution of SIC through the soil profile has had a significant impact on the total C stored in the plow layer, but not on the net C sequestered or released to the atmosphere through land use.