Greenhouse Gas Fluxes From Upper Midwest Corn As Mediated by Rotation.

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.