Effects of elevated CO₂ and agricultural management on flux of greenhouse gases from soil

To evaluate the contribution of agriculture to climate change, the flux of greenhouse gases from different cropping systems must be assessed. Soil greenhouse gas flux (CO₂, N₂O, and CH₄) was assessed during the final growing season in a long-term (10-year) study evaluating the effects of crop management (conservation and conventional) and atmospheric CO₂ (ambient and twice ambient) on a Decatur silt loam (clayey, kaolinitic, thermic Rhodic Paleudults). Seasonal soil CO₂ flux was significantly greater under elevated (4.39 Mg CO₂-C ha ^-1) versus ambient CO₂ (3.34 Mg CO₂-C ha ^-1) and was generally greater in the conventional (4.19 Mg CO ₂-C ha^-1) compared with the conservation (3.53 Mg CO ₂-C ha^-1) system. Soil flux of both N₂O (range, -1.5 to 53.4 g N₂O-N ha^-1 day^-1) and CH ₄ (range, -7.9 to 24.4 g CH₄-C ha^-1 day ^-1) were low throughout the study and rarely exhibited differences caused by treatments. Global warming potential (calculated based on flux of individual gases) was increased by elevated CO₂ (33.4%) and by conventional management (17.1%); these increases were driven primarily by soil CO₂ flux. As atmospheric CO₂ continues to rise, our results suggest adoption of conservation management systems represents a viable means of reducing agriculture's potential contribution to global climate change.