Effects of Elevated Atmospheric CO2 and N Fertilization on Bahiagrass Pastures in the Southeastern U.S.

Abstract

The effects of elevated atmospheric CO₂ on pasture systems remain understudied in the Southeastern US. A 10-year study of bahiagrass (Paspalum notatum Flüggé) response to elevated CO₂ was established in 2005 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. After a year establishment period, N was applied to half of the plots ([(NH₄)₂SO₄] at 90 kg ha^-1 3x yr^-1) while the remaining plots received no N fertilization. These two treatments represent managed and unmanaged pastures, both of which are common in the Southeast. During the course of the study biomass production was assessed at all harvests (3 per yr). Prior to N treatment initiation, biomass production was unaffected by CO₂. Likewise, this pattern remained over the course of the study in plots receiving no N fertilization. In general, biomass production was increased under high CO₂ with N addition; this response was typical of C₄ plants (~15%). In addition to biomass production, treatment effects on tissue C and N will be discussed. Overall, data show that elevated CO₂ can increase biomass productivity with N fertilization.