Nitrogen fertilization of switchgrass increases biomass yield and improves net greenhouse gas balance in northern Michigan, U.S.A

Nitrogen (N) fertilization can increase bioenergy crop production; however, fertilizer production and application can contribute to greenhouse gas (GHG) emissions, potentially undermining the GHG benefits of bioenergy crops. The objective of this study was to evaluate the effects of N fertilization on GHG emissions and biomass production of switchgrass bioenergy crop, in northern Michigan. Nitrogen fertilization treatments included 0 kg ha −1 (control), 56 kg ha −1 (low) and 112 kg ha −1 (high) of N applied as urea. Soil fluxes of CO 2, N 2O and CH 4 were measured every two weeks using static chambers. Indirect GHG emissions associated with field activities, manufacturing and transport of fertilizer and pesticides were derived from the literature. Switchgrass aboveground biomass yield was evaluated at the end of the growing season. Nitrogen fertilization contributed little to soil GHG emissions; relative to the control, there were additional global warming potential of 0.7 Mg ha −1 y −1 and 1.5 Mg ha −1 y −1 as CO 2 equivalents (CO 2eq), calculated using the IPCC values, in the low and high N fertilization treatments, respectively. However, N fertilization greatly stimulated CO 2 uptake by switchgrass, resulting in 1.5- and 2.5-fold increases in biomass yield in the low and high N fertilization treatments, respectively. Nitrogen amendments improved the net GHG benefits by 2.6 Mg ha −1 y −1 and 9.4 Mg ha −1 y −1 as CO 2eq relative to the control. Results suggest that N fertilization of switchgrass in this region could reduce (15–50%) the land base needed for bioenergy production and decrease pressure on land for food and forage crop production. ► We examine the effects of N fertilization of switchgrass on GHG emissions. ► Effects of N fertilization on biomass production of switchgrass bioenergy crop. ► N fertilization contributed little to greenhouse gas emissions. ► N fertilization greatly stimulated CO 2 uptake by the switchgrass. ► N fertilization of switchgrass can help reduce land used for bioenergy production.