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

Authors: Prior, Stephen - Steve; Runion, George; Torbert, Henry - Allen

Submitted to: Soil & Tillage Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/3/2019
Publication Date: 7/12/2019
Citation: Prior, S.A., Runion, G.B., Torbert III, H.A. 2019. Long-term response of a bahaigrass pasture to elevated CO2 and soil fertility management. Soil & Tillage Research. 194:104326. https://doi.org/10.1016/j.still.2019.104326.
DOI: https://doi.org/10.1016/j.still.2019.104326

Interpretive Summary: Both managed and unmanaged pasture systems in the Southeastern US remain understudied agro-ecosystems in terms of the effects of elevated atmospheric CO2 concentration. A long-term bahiagrass pasture study managed with N fertilization or no N fertilization was conducted for 10 years to assess biomass production under ambient or elevated (ambient plus 200 ppm) CO2. These two treatments represent managed and unmanaged pastures, both of which are common in the Southeast. Results show that N fertilization can significantly increase forage biomass production regardless of CO2 level. Elevated CO2 increased forage biomass only when soil N was added. These findings highlight the importance of soil N management to enhance pasture productivity under rising atmospheric CO2 levels.

Technical 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 CO2 concentration. Therefore, we initiated a long-term (10 yr) study of bahiagrass (Paspalum notatum Flüggé) response to elevated CO2 using open top field chambers in 2005 on a Blanton loamy sand (loamy siliceous, thermic, Grossarenic Paleudults). Plants were exposed to ambient or elevated (ambient + 200 ppm) CO2. After a one-year establishment period, an N treatment was applied where half of all plots received N [(NH4)2SO4] at 90 kg/ha three times yearly; the remaining plots received no N fertilization. These two treatments represent managed and unmanaged pastures, both of which are common in the Southeast. Prior to N treatment initiation (establishment phase) biomass production was unaffected by CO2 treatment. Harvests after N treatment initiation (Spring 2006) showed strong effects of N addition on cumulative forage biomass production (~231.8% increase); the main effects of CO2 was also significant (~13.8% increase with elevated CO2). Significant N x CO2 interactions showed that CO2 had no impact on bahiagrass production with no N added (as observed in establishment year); however, forage production was increased (~15.3%) under elevated CO2 with N addition. These findings highlight the importance of soil N management to enhance pasture productivity under rising atmospheric CO2 levels.