Nitrogen Fertilization Affects Bahiagrass Responses to Elevated Atmospheric Carbon Dioxide

Increased atmospheric CO2 and temperature typically lead to greater DM (dry matter) production of grassland plants; however, limited plant N may reduce this response. A 2-yr study (1998-1999) was conducted to evaluate the effects and interactions among at- mospheric CO2, temperature, and N fertilization rate on yield and nutritive value of 'Pensacola' bahiagrass (Paspalum notatum Flugge). Bahiagrass was field grown in Millhopper fine sand (loamy, siliceous Grossarenic Paleudult) under greenhouses with controlled atmo- spheric CO2 and temperature. Atmospheric CO2 levels were 360 and 700 mmol mol 21 , and temperatures were B (baseline, corresponding to ambient in the greenhouse), B 1 1.5C, B 1 3.0C, and B 1 4.5C. Bahiagrass was fertilized at 80 kg N ha 21 (BG-80) or 320 kg N ha 21 (BG-320). Dry matter yield for BG-80 remained the same regardless of CO2 level (7.5 and 6.3 Mg ha 21 in Years 1 and 2), but BG-320 DM yield increased with increasing CO2 concentration in three of four harvests in Year 1 and from 14.8 to 17.3 Mg ha 21 in Year 2. Total N harvested response followed a similar trend as DM yield. Increasing temperature from B to B 1 4.5C had a positive effect on DM yield of BG-80 (23%) and a lesser positive effect on BG-320 (9% increase). Bahiagrass nutritive value increased due to greater N fertilization, but elevated CO2 concentration and temperature had no effect. Nitrogen fertilization affected bahiagrass DM yield response to CO2, but not the nutritive value response to elevated atmospheric CO2 or temperature.