Climate impact and energy return of reed canary grass or tall fescue on marginal land for biogas

Emerging fuels, such as biogas, can be produced from grasses. However, in order not to compete with food production, use of marginal land is preferred. This study compares three systems for biogas production on poorly drained fields in northern Sweden. In the first scenario, reed canary grass (RCG) (Phalaris arundinacea L.) first harvest is used for biogas production while its second, delayed, spring harvest is used for briquette production. In the second and third scenarios, RCG and tall fescue (TF) (Lolium arundinacea Schreb.) respectively were harvested twice per year for biogas production. Energy return on investment (EROI) was highest for RCG to biogas and briquettes, 8.5, while RCG to biogas gave 7.8 and TF to biogas 8.3. The higher EROI for TF to biogas compared to RCG to biogas is caused by a higher specific methane production per kg organic matter. Net climate impact was lowest for RCG to biogas, 6.9 g CO2 eq. MJ–1 energy output, and highest for TF to biogas, 7.6 g CO2 eq. MJ–1. This was largely due to longer duration of the RCG swards (10 years) than TF swards (3 years). All systems had quite similar climate impact and EROI so farmers can choose the system most suitable for their conditions.