Nitrous oxide (N2O) and methane (CH4) emitted by anthropogenic activities have been linked to the observed and predicted climate change. Conservation tillage practices such as no-tillage (NT) have potential to increase C sequestration in agricultural soils but patterns of N2O and CH4 emissions associated with NT practices are variable. Thus, the objective of this study was to evaluate the effects of tillage practices on N2O and CH4 emissions in long-term continuous corn (Zea mays) plots. The study was conducted on continuous corn experimental plots established in 1962 on a Crosby silt loam (fine, mixed, mesic Aeric Ochraqualf) in Ohio. The experimental design consisted of NT, chisel till (CT) and moldboard plow till (MT) treatments arranged in a randomized block design with four replications. The N2O and CH4 fluxes were measured for 1-year at 2-week intervals during growing season and at 4-week intervals during the off season. Long-term NT practice significantly decreased soil bulk density (rho(b)) and increased total N concentration of the 0-15 cm layer compared to MT and CT. Generally, NT treatment contained higher soil moisture contents and lower soil temperatures in the surface soil than CT and MT during summer, spring and autumn. Average daily fluxes and annual N2O emissions were more in MT (0.67 mg m(-2) d(-1) and 1.82 kg N ha(-1) year(-1)) and CT (0.74 mg m(-2) d(-1) and 1.96 kg N ha(-1) year(-1)) than NT (0.29 mg m(-2) d(-1) and 0.94 kg N ha(-1) year(-1)). On average, NT was a sink for CH4, oxidizing 0.32 kg CH4-C ha(-1) year(-1), while MT and CT were sources of CH4 emitting 2.76 and 2.27 kg CH4-C ha(-1) year(-1), respectively. Lower N2O emission and increased CH4 oxidation in the NT practice are attributed to decrease in surface rho(b), suggesting increased gaseous exchange. The N2O flux was strongly correlated with precipitation, air and soil temperatures, but not with gravimetric moisture content. Data from this study suggested that adoption of long-term NT under continuous corn cropping system in the U.S. Corn Belt region may reduce GWP associated with N2O and CH4 emissions by approximately 50% compared to MT and CT management.
