Effects of Elevated Atmospheric Co2 on Soil Co2 Efflux in Conventional and Conservation Cropping Systems

Elevated atmospheric carbon dioxide (CO2) can affect both the quantity and quality of plant tissues produced, which will impact the cycling and storage of carbon (C) within plant/soil systems and thus the rate of CO2 release back to the atmosphere. Research is needed to more accurately quantify the effects of elevated CO2 and associated feedbacks on soil CO2 efflux in order to predict the potential of terrestrial ecosystems to sequester C. Effects of elevated atmospheric CO2 on soil CO2 efflux were examined in a long-term study comparing row crops managed as either a conventional or a conservation tillage system. In the conventional system, grain sorghum and soybean were rotated each year using conventional tillage practices and winter fallow. The conservation system also uses a grain sorghum­ soybean rotation, with three winter cover crops: wheat, crimson clover, and sunn hemp which were also rotated. All crops in the conservation system were grown using "no-till" practices. Plants were exposed to either 365 ppm (ambient) or 725 ppm (elevated) levels of atmospheric CO2 using open top field chambers. Soil CO2 efflux, over a full two-year cropping cycle, was increased by both elevated atmospheric CO2 and by conservation management; these increases were due, primarily, to increased biomass inputs from these treatments. Implications of these data on soil carbon storage in these systems will be discussed.