Combining GHG Emissions and Soil Carbon Changes as a Single Metric to Evaluate Agricultural Policy Promoting Biomass for Biofuels

Abstract: Incorporating a multi-year grass ley into an arable crop rotation can increase soil organic carbon stocks, reduce carbon emissions and provide feedstock for biogas. This thesis set out to study how a policy promoting agricultural biomass for biogas impacts GHG emissions and carbon sequestration on a regional level over a temporal scale of 20 years. This was done in the specific case of policy promotion of an increased cultivation of two-year grass leys in the Swedish intensive-farming region Götalands Södra Slättbygder (GSS), to a 15% ley cover of the arable land belonging to the high intensity farms. This was studied by combining life cycle analysis methodology with a dynamic economic model, to provide a holistic overview of the impacts on carbon changes in the region. The results showed that the implementation the leys led to a decrease in the total, annual impact from agricultural processes in the magnitude of 22-23% . It also led to a decrease in total impact per the functional unit’s cereal unit (9%) and price (18%) in the 20th year. However, the implementation also led to a 15% decrease in food production. The food production also decreased over time in the reference scenario due to decreasing SOC stocks, although the decrease was lower than in the scenario with the added leys. The implementation of leys in specialised crop rotations have the potential to decrease regional GHG emissions from the agricultural processes, while also reducing the rate of loss of SOC content, but it might come at a cost of food loss and iLUC. However, not taking action against decreasing SOC stocks will also lead to loss of food production. Furthermore, methodological choices for the accounting of impacts from soil organic carbon changes were found to have a large impact on the results.