Greenhouse gas fluxes from no-till rotated corn in the upper midwest

• Four years of greenhouse gas fluxes reported from no-till, dryland corn
• Annual N2O and CH4 fluxes ranged between 0.8 and 1.6 kg N or C per ha.
• CH4 fluxes became positive with annually-increasing soil moisture.
• Rotation (2-yr versus 4-yr) did not affect gas fluxes from corn.
• 4-yr rotation accrued sufficient soil C to offset global warming potential of gases.

We determined soil surface fluxes of greenhouse gases (carbon dioxide, nitrous oxide, methane) from no-till, dryland corn (Zea mays L.) in eastern South Dakota and tested the effect of rotation on greenhouse gas fluxes from corn. The corn was grown within a randomized, complete block study that included both a 2-year (corn–soybean) rotation and a 4-year (corn-field peas–winter wheat–soybean) rotation with plots containing the corn phase present in every year, 2007–2010. Annual carbon dioxide (CO2) fluxes were between 1500 and 4000 kg CO2–C ha−1 during the four-year study. Annual nitrous oxide (N2O) fluxes ranged from 0.8 to 1.5 kg N2O–N ha−1 with peak fluxes during spring thaw and following fertilization. Net methane (CH4) fluxes in 2007 were close to zero, while fluxes for 2008–2010 were between 0.9 and 1.6 kg CH4–C ha−1. Methane fluxes increased with consistently escalating values of soil moisture over the four-year period demonstrating that soils which previously exhibited neutral or negative CH4 flux may become net CH4 producers in response to multiyear climatic trends. No significant differences in gas fluxes from corn due to treatment (2-year vs. 4-year rotation) were observed. Mean net annual soil surface gas fluxes from corn calculated over four years for both treatments were 2.4 Mg CO2–C ha−1, 1.2 kg N2O–N ha−1, and 0.9 kg CH4–C ha−1. Annual global warming potentials (GWP) as CO2 equivalents were 572 kg ha−1 and 30 kg ha−1 for N2O and CH4, respectively. Measurements of soil carbon showed that the 4-yr rotation accrued 596 kg C ha−1 yr−1 in the top 30 cm of soil which would be more than sufficient (2.19 Mg CO2 eq ha−1 yr−1) to offset the annual GWP of the nitrous and methane emissions from corn. In contrast, the 2-year rotation lost 120 kg C ha−1 yr−1 from the top 30 cm of soil resulting in corn being a net producer of greenhouse gases and associated GWP.