2008 Joint Annual Meeting (5-9 Oct. 2008): Greenhouse Gas Flux from Agricultural Soils: Impacts of 10 Years of Management and Elevated Co₂

An evaluation of the soil efflux of greenhouse gases (CO₂, N₂O, and CH₄) from a conservation and conventional tillage system that has been under the influence of elevated atmospheric CO₂ for the past 10 years will be presented. Fluxes of all greenhouse gases were significantly (p<0.05) greater under elevated vs. ambient CO₂ regardless of tillage system effects. Carbon dioxide flux was generally greater in the conventional tillage system; however on two sampling dates following a large rain event in the summer months, flux from the conservation tillage system was slightly, but significantly, greater than in the conventional system. Methane fluxes were generally low with the conservation tillage system having lower fluxes than the conventional system. In addition, on several dates, the conservation system acted as a greater sink for CH₄ than the conventional system; however the conventional system acted as a greater sink for CH₄ on one date. Interestingly, the flux of N₂O from the conventional system remained low throughout the study period; when looking only within the ambient levels of atmospheric CO₂, the conservation system generally had lower fluxes of N₂O. However, when looking across atmospheric CO₂ level, a large flux of N₂O was observed in the conservation system that had been exposed to elevated atmospheric CO₂ for 10 years. The impacts of these systems and the fluxes of the measured greenhouse gases on the global warming potential of these two systems will be discussed.