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 atmospheric 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 atmospheric CO2 and temperature. Atmospheric CO2 levels were 360 and 700 mu mol mol(-1), and temperatures were B (baseline, corresponding to ambient in the greenhouse), B + 1.5 degrees C, B + 3.0 degrees C, and B + 4.5 degrees C. Bahiagrass was fertilized at 80 kg N ha(-1) (BG-80) or 320 kg N ha(-1) (BG-320). Dry matter yield for BG-80 remained the same regardless of CO2 level (7.5 and 6.3 Mg ha(-1) in Years I 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(-1) in Year 2. Total N harvested response followed a similar trend as DM yield. Increasing temperature from B to B + 4.5 degrees C 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.