Land‐use change to bioenergy production in <scp>E</scp>urope: implications for the greenhouse gas balance and soil carbon

Abstract

Abstract Bioenergy from crops is expected to make a considerable contribution to climate change mitigation. However, bioenergy is not necessarily carbon neutral because emissions of CO 2 , N 2 O and CH 4 during crop production may reduce or completely counterbalance CO 2 savings of the substituted fossil fuels. These greenhouse gases ( GHG s) need to be included into the carbon footprint calculation of different bioenergy crops under a range of soil conditions and management practices. This review compiles existing knowledge on agronomic and environmental constraints and GHG balances of the major E uropean bioenergy crops, although it focuses on dedicated perennial crops such as M iscanthus and short rotation coppice species. Such second‐generation crops account for only 3% of the current E uropean bioenergy production, but field data suggest they emit 40% to &gt;99% less N 2 O than conventional annual crops. This is a result of lower fertilizer requirements as well as a higher N‐use efficiency, due to effective N‐recycling. Perennial energy crops have the potential to sequester additional carbon in soil biomass if established on former cropland (0.44 Mg soil C ha −1 yr −1 for poplar and willow and 0.66 Mg soil C ha −1 yr −1 for M iscanthus ). However, there was no positive or even negative effects on the C balance if energy crops are established on former grassland. Increased bioenergy production may also result in direct and indirect land‐use changes with potential high C losses when native vegetation is converted to annual crops. Although dedicated perennial energy crops have a high potential to improve the GHG balance of bioenergy production, several agronomic and economic constraints still have to be overcome.