Greenhouse Gas Balances in Bioenergy Production Systems: Measurement, Simulation and Assessment.

The European Union aims to reach a share of renewable energy source of 20% in 2020. In Germany currently about 7.6% of the total primary energy consumption is delivered from bioenergy sources, including energy from dedicated energy crops and fire wood. Bioenergy crops thereby occupy about 2 million ha or 16% of the arable land. For the biofuel pathway minimum GHG mitigation goals are in force based on specific CO2-emission reduction per unit energy of biofuel. For mitigation calculation the direct and indirect emissions of N2O play a major role, but methods based on IPCC national inventory emission factors may not be suitable for optimizing GHG balances on specific sites in terms of N rates, other management factors including the choice of the energy crop. Results from two three year collaborative research projects in Germany were yields and N2O-emissions were measured for oilseed rape and silage maize on 5 sites will be presented. In general, N2O emission rates were lower than the IPCC emission factors suggest but large differences between crops, sites and years exist. The data are analyzed with a dynamic simulation model capable of predicting yield and direct and indirect N2O-emission responses to N rate in interaction with soil and weather conditions. The effects on GHG balances and specific CO2-emission are calculated and discussed.