We used the flux chamber technique to measure greenhouse gas (carbon dioxide, nitrous oxide, methane) fluxes from replicated corn plots located in eastern South Dakota.� The corn was grown within a randomized, complete block study that included both a two year (corn-soybean) rotation and a four-year (corn/field peas/winter wheat/soybean) rotation with plots containing the corn phase present in every year, 2006-2009.� Annual carbon dioxide fluxes were between 1000 and 1500 kg CO₂-C ha for three of the four years. In 2007, which had above-normal temperatures, CO₂ fluxes were about 3500 kg/ha. �CO₂ fluxes generally tracked temperature and precipitation events.� Nitrous oxide fluxes were less than <0.5 kg N₂O-N/ha in 2006, about 1 kg/ha in 2007 and 0.7 kg/ha in 2008 and 2009. �N₂O fluxes peaked during spring thaw and following fertilization. Methane fluxes in 2006 were <0.5 kg N₂O-N/ha with some plots serving as a small sink.� In 2007, methane fluxes were neutral, while in 2008 and 2009 methane fluxes averaged about 0.6 kg CH₄-C/ha.� Methane fluxes varied with soil moisture.� Relatively high variations were observed among chambers within the same plot and among plots within a single treatment.� No significant differences in gas fluxes due to treatment (2 yr vs. 4 yr rotation) were observed.� These ground-based data bound estimates of gas fluxes from corn grown in high organic matter (ca. 4%) Mollisols under rain-fed conditions in the sub-humid climate (58 cm mean annual precipitation) and mean annual temperature of 8�C of the northwestern U.S. corn belt. This research is part of the USDA-ARS GRACEnet program.