Rapeseed is an efficient energy crop which can still improve

The ability of biofuels to contribute efficiently to the replacement of fossil energy and to the reduction of greenhouse gas emissions has been a matter of debate. Hence, there is a need to assess accurately the energy balance of biofuels and their ability to reduce greenhouse gas emissions, in order to evaluate and to improve the benefit for society. In rapeseed, the energy ratio (energy produced per unit of non-renewable energy input) is well above 2 whatever the method of calculation. In order to investigate the variability of energy ratios and to identify ways of improvement, a study was conducted in France in 2005 and 2006. The method of mass allocation of input energy was used for calculations, instead of the substitution method, because with this method the results do not depend on the utilization of co-products. Hence, this method is better adapted to follow improvements. A great variability in the energy ratio was observed in 2005 and 2006. Seed yields and energy cost of fertilizer N explained most of this variability. Hence, improvements should focus on increasing yield with little increase in energy cost, and on decreasing wasting of N fertilizer. However the farmer incomes, and the net production of energy per hectare, must also be a matter of concern. The inventories of greenhouse gas emissions of biofuels are still uncertain because of the great variability of soil emissions, due to environmental and management factors. Hence, in order to assess the effect of rapeseed on greenhouse gas emissions, methods based on process-oriented models accounting for these factors must be used. Such models give promising results, but further testing is still needed.