Growing season greenhouse gas flux from switchgrass in the northern great plains

Switchgrass (Panicum virgatum L.) is being evaluated as a bioenergy crop for the northern Great Plains. Field measurements of CO2, CH4, and N2O flux are needed to estimate the net greenhouse gas (GHG) balance of this biofeedstock. The study objective was to determine effects of recommended Nitrogen (N) fertilization (67 kg ha−1 of N applied) and unfertilized switchgrass on growing season soil-atmosphere CO2, CH4, and N2O flux using static chamber methodology. Mean hourly CO2 flux was greatest during periods of active switchgrass growth and was similar between N fertilizer treatments (P = 0.09). Mean hourly N2O flux was consistently greater under N fertilization than without N throughout the growing season. Overall, N fertilization of switchgrass affected cumulative growing-season N2O flux (27.6 kg ha−1 ± 4.0 kg ha−1 vs. 86.3 kg ha−1 ± 14.3 kg ha−1 as CO2 equivalents (CO2eq) for 0 kg ha−1 and 67 kg ha−1 of N applied, respectively; P < 0.01), but not cumulative CO2 or CH4 flux (P = 0.08 and 0.51, respectively). Aboveground biomass production was greater with N application (6.8 Mg ha−1 ± 0.5 Mg ha−1 dry matter) than without N (3.2 Mg ha−1 ± 0.5 Mg ha−1) (P < 0.05). Net greenhouse gas intensity (GHGI; kg GHG flux kg−1 harvest yield as CO2eq) for switchgrass production was similar between N treatments (0.71 vs. 0.44 for 0 kg ha−1 and 67 kg ha−1 of N applied, respectively; P = 0.18).