Growing high input crops, double cropping, and reducing or eliminating tillage have been shown to increase soil organic carbon (SOC) levels and these practices have been suggested as means to mitigate anthropogenic greenhouse gas (GHG) emissions. However, all 3 important biogenic GHG’s (CO₂, N₂O, CH₄) must be considered to fairly evaluate the impacts of different land management strategies. Fluxes of all 3 gases are rarely measured in field plots due to practical and monetary constraints. But models that simulate the processes that control GHG fluxes can be readily used to compare how land management affects GHG’s and other variables such as NO₃ leaching. The DAYCENT biogeochemical model was tested using crop yield and SOC data from 24 fields representing 3 soil series, different crop rotations, and different tillage intensities. Comparison of observed and simulated crop yields and SOC levels yielded r² values of 0.74 and 0.61, respectively. DAYCENT was then used to project SOC changes, direct and indirect N₂O emissions, CH₄ uptake, and NO₃ leaching from 2006-2020. Net GHG flux was calculated for 3 tillage alternatives: plow before all crops are planted, plow only before small grains are planted, and never plow. Model results suggest that as tillage intensity decreases, SOC sequestration increases substantially while N₂O emissions, CH₄ uptake, and NO₃ leaching can increase or decrease by small amounts. After converting fluxes of all 3 gases to CO₂-C equivalents and accounting for the CO₂ emissions associated with production of nitrogen fertilizer, DAYCENT projected that these soils will remain net GHG sinks or neutral under no till until at least 2020 but emit significant amounts of GHG’s if they are regularly tilled.