Biofuel production is considered a promising strategy for reducing the net emissions of CO2 into the atmosphere and decreasing dependence on fossil fuels. Hence interest in energy production from renewable biomass is increasing worldwide. However, biofuel production also implies a decrease in the return of carbon (C) rich crop residues to the soil, which is replaced with nitrogen (N) rich by-products of biofuel production (BBPs). This may profoundly affect the greenhouse gas (GHG) balance of the soil, both through a decrease in the soil organic carbon content (CO2 emission), and through an increase in N2O emission from mineralized N. However, no scientific data is available to quantify this effect. Research on the effects of biofuel production on the GHG balance of the soil is therefore needed to complete the life cycle analysis (LCA) of biofuel production. The aim of this proposal is to quantify the effect of BBPs applied to the soil on GHG emissions and related N and C dynamics in the soil. We will work with by-products of the three main bioenergy chains: (i) bioethanol from wheat; (ii) biodiesel from rapeseed; and (iii) biogas from anaerobic digestion of silage maize. In a series of laboratory incubation experiments, the C and N mineralization of the various BBPs will be assessed in relation to crop residue and N fertilizers. The fate of C from crop residue and BBPs in the soil organic matter fractions of increasing stability will be quantified using 13C tracing. The combined effect of changes in SOC and N2O emission will be expressed in terms of global warming potential to complete the LCA of the various biofuel chains.