Biofuels from bioenergy crops may substitute a significant part of fossil fuels in the transport sector where, e.g., the European Union has set a target of using 10% renewable energy by 2020. Savings of greenhouse gas emissions by biofuels vary according to cropping systems and are influenced by such regional factors as soil conditions, climate and input of agrochemicals. Here we analysed at a regional scale the greenhouse gas (GHG) emissions associated with cultivation of winter wheat for bioethanol and winter rapeseed for rapeseed methyl ester (RME) under Danish conditions. Emitted CO2 equivalents (CO2eq) were quantified from the footprints of CO2, CH4 and N2O associated with cultivation and the emissions were allocated between biofuel energy and co-products. Greenhouse gas emission at the national level (Denmark) was estimated to 22.1 g CO2eq MJ−1 ethanol for winter wheat and 26.0 g CO2eq MJ−1 RME for winter rapeseed. Results at the regional level (level 2 according to the Nomenclature of Territorial Units for Statistics [NUTS]) ranged from 20.0 to 23.9 g CO2eq MJ−1 ethanol and from 23.5 to 27.6 g CO2eq MJ−1 RME. Thus, at the regional level emission results varied by up to 20%. Differences in area-based emissions were only 4% reflecting the importance of regional variation in yields for the emission result. Fertilizer nitrogen production and direct emissions of soil N2O were major contributors to the final emission result and sensitivity analyses showed that the emission result depended to a large extent on the uncertainty ranges assumed for soil N2O emissions. Improvement of greenhouse gas balances could be pursued, e.g., by growing dedicated varieties for energy purposes. However, in a wider perspective, land-use change of native ecosystems to bioenergy cropping systems could compromise the CO2 savings of bioenergy production and challenge the targets set for biofuel production.
Acta Agriculturae Scandinavica. Section B. Soil and Plant Science, 2013, Vol 63, Issue 3, p. 219-230