Venterea, Rodney (USDA-ARS, 1991 Upper Buford Circle, 439 Borlaug Hall, University of Minnesota, St. Paul, MN, 55108; Phone: 612-624-7842; Fax: 651-649-5174; Email: venterea@umn.edu)

Nitrous Oxide and Methane Emissions Under Varying Tillage and Fertilizer Management

R. Venterea*, M. Burger, K. A. Spokas

Reduced tillage is being examined as a means of enhancing soil carbon and mitigating greenhouse gas (GHG) emissions. There is relatively little information regarding tillage effects on emissions of nitrous oxide (N₂O) and methane (CH₄), which have higher global warming potentials than carbon dioxide (CO₂). We used chambers to measure N₂O and CH₄ fluxes in plots maintained under differing tillage treatments since 1991. Emissions of N₂O following broadcast urea (BU) application were higher under no till (NT) and conservation tillage (CsT) compared to conventional tillage (CT). In contrast, following anhydrous ammonia (AA) injection, N₂O emissions were higher under CT and CsT compared to NT. Emissions following urea ammonium nitrate (UAN) application did not vary with tillage. Total growing season non-CO₂ GHG emissions were dominated by N₂O, and were equivalent to soil C losses of 0.07 – 0.50 Mg C ha^-1 y^-1. Uptake of CH₄ during the drier of the two seasons (2003) was two to three times higher than during 2004. Emissions of N₂O from AA-amended soils exceeded emissions from the UAN and BU treatments. This study demonstrates that tillage effects on N₂O emissions depend on fertilizer management and that non-CO₂ GHG emissions can contribute substantially to the total GHG budget of agro-ecosystems in the upper mid west U.S.