Long-term response of bahaigrass pastures to elevated atmospheric CO2 and fertility management: Forage quality

Authors: Prior, Stephen; Runion, George; Torbert Iii, Henry

Submitted to: Soil & Tillage Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/20/2025
Publication Date: 6/24/2025
Citation: Prior, S.A., Runion, G.B., Torbert III, H.A. 2025. Long-term response of bahaigrass pastures to elevated atmospheric CO2 and fertility management: Forage quality. Soil & Tillage Research. 254:106727. https://doi.org/10.1016/j.still.2025.106727.
DOI: https://doi.org/10.1016/j.still.2025.106727

Interpretive Summary: Southeastern US pasture systems remain understudied as impacted by elevated atmospheric CO2 concentration. A long-term bahiagrass pasture study investigated responses to elevated CO2 under fertilized (managed) and unfertilized conditions (unmanaged). In comparison to unmanaged pastures, fertilization clearly increased productivity and forage quality (e.g., forage N, crude protein, digestible protein) indicating that bahiagrass pastures in the southeastern US would benefit from proper soil fertility management. Despite reductions in some forage elemental concentrations under managed conditions, all nutrients expressed on a land area basis (content) were increased and may impact animal nutrition. Effects of elevated CO2 were much smaller and less consistent which may be reflective of a long-term C4 plant response. Additional research is required to determine if these findings can be generalized for other southeastern pastures.

Technical Abstract: Southeastern US pasture systems remain understudied agro-ecosystems as affected by elevated atmospheric CO2 concentration. A long-term study of bahiagrass (Paspalum notatum Flüggé) assessed responses to elevated CO2 on a Blanton loamy sand (loamy siliceous, thermic, Grossarenic Paleudults). Pastures were exposed to ambient or elevated (ambient plus 200 µmol mol-1) CO2 using open top field chambers. Based on extension soil test recommendations, half of all plots received N [(NH4)2SO4] at 90 kg ha-1 three times yearly plus K, P, and lime (managed) while remaining plots received no fertilization (unmanaged). For 10 years, bahiagrass from all treatments were assessed for impacts on forage quality using forage from yearly August harvests. These routine analyses included, crude protein, acid detergent fiber, neutral detergent fiber, lignin, total digestible nutrient, relative forage quality, NO3-N, digestible protein, crude fiber, net energy calculations, metabolizable energy and elemental concentrations (C, N, P, K, Ca, Mg, B, Cu, Fe, Mn, Na, and Zn). Fertilization clearly increased productivity and forage quality (e.g., forage N, crude protein, digestible protein) indicating that southeastern US bahiagrass pastures would benefit from proper soil fertility management. Despite reductions in some forage elemental concentrations under managed conditions, nutrients expressed on a land area basis (content) were increased. Effects of elevated atmospheric CO2 were much smaller and less consistent which may be reflective of a long-term C4 plant response. Additional research is required to determine if our findings are applicable to other southeastern pasture systems.