First or second generation biofuel crops in Brandenburg, Germany? A model-based comparison of their production-ecological sustainability

• Miscanthus and black locust are resource-efficient, low impact biofuel crops.
• Black locust produces biomass on degraded soils and rehabilitates these soils.
• Sugarbeet and rapeseed are resource-inefficient, high impact biofuel crops.

We assessed and compared the production-ecological sustainability of first and second generation biofuel production systems in the state of Brandenburg, Germany. Production ecological sustainability was defined by a limited set of sustainability indicators including net energy yield per hectare, GHG emissions, N leaching, soil organic carbon and soil erosion, and several resource use efficiencies. The assessed first generation fuels are biodiesel and bioethanol produced from rapeseed (Brassica napus L.) and sugarbeet (Beta vulgaris L.) feedstock, respectively. Assessed second generation systems are based on feedstock from Miscanthus (Miscanthus × giganteus Greef et. Deu. ex Hodkinson et Renvoize) and black locust (Robinia pseudoacacia L.); for both crops conversion into cellulosic ethanol and Fischer Tropsch Diesel was assessed. In the assessment, computer models were used for simulating crop growth, soil organic carbon dynamics and several other relevant biophysical processes. Second generation biofuel production systems based on Miscanthus and black locust perform substantially better than first generation systems based on rapeseed and sugarbeet. They contribute much more to GHG emission reduction, had much higher net energy yields and better resource use efficiencies; soil erosion and N leaching were also lower. Miscanthus performed better than black locust, except for its N use efficiency; it is the most water-efficient species, which is important in a region with declining groundwater tables. However, in Brandenburg, low temperatures during winter and early spring are often threatening to survival of first-year Miscanthus plantings; there have been disastrous experiences in the past. The drawback of black locust is that it has invasive characteristics; this risk may be controllable however (cf. Motta et al., 2009). Of the first generation systems, rapeseed has low net energy yields and large N requirements per unit of energy produced; it also performed poorly for N leaching. Erosion hazard in rapeseed is especially present after the seedbed has been prepared at the end of summer. Greatest erosion risk was calculated for sugarbeet however, due to its late canopy closure.