Long-term response of a bahiagrass pasture to elevated CO2 and soil fertility management

Abstract Pastures represent a significant portion of the rural landscape in the southeastern US, yet remain understudied agro-ecosystems in terms of the effects of rising atmospheric CO 2 concentration. Therefore, in 2005 we initiated a long-term (10 yr) study of bahiagrass ( Paspalum notatum Flugge) response to elevated CO 2 using open top field chambers on a Blanton loamy sand (loamy siliceous, thermic, Grossarenic Paleudults). Plants were exposed to ambient or elevated (ambient + 200 μmol mol −1 ) CO 2 . After a one-year establishment period, a management (M) treatment was applied where half of all plots received N [(NH 4 ) 2 SO 4 ] at 90 kg ha −1 three times yearly plus P, K, and lime as recommended by soil testing; the remaining plots received no fertilization. These two treatments represent managed and unmanaged pastures, both of which are common in the Southeast. Prior to M treatment initiation (establishment phase) biomass production was unaffected by CO 2 treatment. Harvests after M treatment initiation (Spring 2006) showed strong effects of fertilizer addition on cumulative forage biomass production (˜231.8% increase); the main effect of CO 2 was also significant (˜13.8% increase with elevated CO 2 ). Significant M x CO 2 interactions showed that CO 2 had no impact on bahiagrass production with no fertilizer added (as observed in establishment year); however, forage production was increased (˜15.3%) under elevated CO 2 with fertilizer addition. These findings highlight the importance of soil fertility management to enhance pasture productivity under rising atmospheric CO 2 levels.