Long-Term Pasture Under Elevated CO2 and N Management: CO2 Flux Patterns upon Return to Cultivation.

Soil CO₂ efflux patterns associated with converting pastures back to row crop production remain understudied in the Southeastern US. A 10-year study of bahiagrass (Paspalum notatum Flüggé) response to elevated CO₂ was conducted using open top field chambers on a Blanton loamy sand (loamy siliceous, thermic, Grossarenic Paleudults). Plants were subjected to ambient or elevated (ambient plus 200 ppm) CO₂ and grown under managed ([(NH₄)₂SO₄] at 90 kg ha^-1 3x yr^-1) and unmanaged conditions (no added N), both of which are common in the Southeast. At study termination, soil CO₂ flux was continuously monitored (automated carbon efflux system or ACES) following glyphosate applications and tillage to document CO₂ loss associated with pasture conversion to row crop production. Concurrent measures of the herbicide termination process were documented with an active light sensor (Greenseeker meter). Over the course of this study, biomass production was increased under high CO₂ with N addition; this response was typical of C₄ plants (~15%). In contrast, biomass production was unaffected by CO₂ without added N. The effects of elevated CO₂ and N management on soil CO₂ efflux patterns associated with herbicide treatment and tillage will be discussed.