Submitted to: Journal of Environmental Quality
Publication Type: Peer reviewed journal
Publication Acceptance Date: 4/28/2005
Publication Date: 9/1/2005
Citation: Venterea, R.T., Burger, M., Spokas, K.A. 2005. Nitrogen oxide and methane emissions under varying tillage and fertilizer management. Journal of Environmental Quality. 34:1467-1477. Interpretive Summary: The objective of the current study was to examine the impact of long-term tillage management, together with fertilizer practices, on nitrous oxide (N2O), nitric oxide (NO), and methane (CH4) gas emissions within a corn/soybean rotation in southeastern Minnesota. Nitrous oxide and CH4 are potent greenhouse gases, and NO emissions can affect tropospheric ozone (O3) production, particularly in rural regions. We used static and dynamic chambers to measure gas fluxes over two consecutive growing seasons. The results indicated that N2O emissions can either be enhanced, or mitigated, with reduced tillage depending on the type of fertilizer management employed. They also indicated that total growing season N2O + CH4 emissions were a significant component of the total greenhouse gas budget. Emissions of NO, and the ratio of NO:N2O emissions, were also affected by the type of fertilizer management used. The results demonstrate that the potential for reduced tillage agriculture to mitigate total greenhouse gas emissions depends only in part on its effectiveness in sequestering soil carbon (C). These results will impact policies and recommendations regarding C sequestration via reduced tillage as a means of mitigating global warming. Such recommendations will need to consider that fertilizer and tillage management effects may interact in affecting total greenhouse gas emissions.
Technical Abstract: Reduced tillage agriculture is being examined as a means of enhancing soil (C) levels and mitigating the impact of agriculture on greenhouse gas (GHG) emissions. There is relatively little information regarding tillage, and other management effects, on emissions of non CO2 GHGs and other trace gases. We used static and dynamic chambers to measure fluxes of nitrous oxide (N2O), nitric oxide (NO) and methane (CH4) in plots maintained under differing tillage treatments since 1991. Over two consecutive growing seasons of corn rotated with soybean, N2O emissions following post-plant application of 100 kg N ha-1 as broadcast urea (BU) were higher under no till (NT) and conservation tillage (CsT) compared to conventional tillage (CT). In the subsequent season, the effect of tillage on N2O emissions varied with fertilizer management. Following pre-plant treatment with an equal amount of anhydrous ammonia (AA), N2O emissions were higher under CT and CsT compared to NT, while emissions following the application of urea ammonium nitrate (UAN) did not vary with tillage. Emissions of NO under NT were significantly higher under CT when fertilized with AA, but otherwise were not affected by tillage. Emissions of NO and the ratio of NO:N2O were highest under BU. Total NO + N2O losses were not affected by tillage, but were higher by a factor of two under both AA and BU compared to UAN. Total growing season non-CO2 GHG emissions were estimated to be equivalent to soil C loss rates of 0.07 - 0.50 Mg C ha-1 y-1, and therefore to be a significant component of the total GHG budget. Most importantly, these results indicate that N2O emissions can either be enhanced, or mitigated, with reduced tillage depending on the type of fertilizer management employed.