Submitted to: International Soil Tillage Research Organization Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: 8/25/2015
Publication Date: 9/14/2015
Citation: Prior, S.A., Runion, G.B., Torbert III, H.A. 2015. Response of a southeastern U.S. bahiagrass pasture to elevated atmospheric CO2 and N fertilization. In: Sustainable Intensification for Increased Food Energy, 20th International Conference of the International Soil Tillage Research Book of Abstracts, September 14-18, 2015, Nanjing, China. p. 100.
Technical Abstract: In the Southeastern US both managed and unmanaged pasture systems remain understudied agro-ecosystems in terms of the effects of elevated atmospheric CO2 concentration. Therefore, we initiated a long-term 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). The study has run for 9 years with biomass production and tissue carbon and nitrogen assessed. Plants were exposed to ambient or elevated (ambient plus 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-1 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 (Summer 2006) showed a strong effect of N treatment on cumulative biomass production (>300% increase with N); the main effect of CO2 was also significant (16% increase with high CO2). A significant interaction between treatments showed that CO2 had no impact on bahiagrass production with no N added (as observed in establishment year); however, biomass production was increased by 21% under high CO2 with N added. In general, this same pattern of treatment response has been observed in subsequent years. Tissue C concentration was unaffected by CO2 treatment, while N concentration was slightly reduced under high CO2. However, total C content was usually higher under elevated CO2 while total N content was unaffected by CO2. For C:N ratio, a treatment interaction indicated that high CO2 grown plants had lower C:N in the no N treatment, but the opposite was observed with N fertilization. As with biomass, this same general pattern was observed in subsequent years. Results to date show that N fertilization can increase biomass productivity under elevated CO2, but forage quality (in terms of C:N ratio) may decline slightly. Efforts are also underway to assess impacts of these treatments on belowground biomass, soil trace gas efflux, and soil carbon storage.