Predicted Soil Management and Climate Change Effects on SOC in South Carolina.

Extensive use of inversion tillage has contributed to the loss of soil organic carbon (SOC) and degraded soil health in the southeast U.S.A. Our objective was to predict changes in SOC in a Norfolk loamy sand in Florence, SC under several crop rotations (corn (Zea mays L.)-cotton (Gossypium ssp.), C-CT; corn-soybean (Glycine max (L.) Merr.), C-SB; sorghum (Sorghum bicolor (L.) Moench)-soybean, SG-SB; sorghum-cotton, SG-CT; C-CT or C-SB with Rye (Secale cereale L.); and C-SB or SG-SB with double-cropped winter wheat (Triticum aestivum L.), WW)), and tillage practices (conventional (CvT) and conservation (CnT) tillage), predicted  changes in precipitation and air temperature under expected responses of climate change, and crop yield growth rates. CQESTR, a process-based C model, was fitted with 12 years of crop production and SOC data (2002-2013) and then used to predict changes in SOC through 2033. The model predicted change in SOC at the 0-15 cm soil depth was significantly correlated (r = 0.98) with annualized biomass inputs and ranged from -4.19 Mg C ha^-1 with SG-CT to 8.69 Mg C ha^-1 with C-SB w/Rye over the period of 2014-2033. Conservation tillage was predicted to increase SOC content 4 to 17% under six of eight crop rotations. Climate change was predicted to change SOC by -0.8 to -6.6%, compared to 6 to 16% when current crop yield growth rates were factored into the model simulations. High residue producing crop rotations such as corn and/or winter crops in combination with CnT are likely the best management practices to maximize soil C sequestration; however, conservation practices with the ability to increase SOC deeper in the soil profile may be necessary for long-term SOC accumulation.