Is agricultural management promoting carbon sequestration better for the climate? Comparing the carbon footprint of intervention management and conventional management using an LCA

Sammanfattning

Improved management of agricultural soils to sequester carbon from the atmosphere is considered an important climate mitigation measure. Intensive agriculture often leads to degradation of soil organic carbon (SOC), contributing to climate change and loss of soil ecosystem services. Interventions in agricultural management can halt or reverse the loss of SOC. Annual SOC change rates for intervention and conventional management were taken from a review on long-term time series data. The purpose of this study is to compare the GHG emissions of management scenarios from a life cycle perspective. The intervention scenario differs from the conventional scenario by using manure to replace inorganic fertiliser, having reduced tillage, and leaving crop residues in the field. Production functions were used to describe the relationship between SOC, nutrient inputs and yields. Using life cycle assessment (LCA) methods, the greenhouse gas (GHG) emissions of each scenario are estimated based on regional data combined with a LCA database. The functional unit is yields converted into cereal units for a full crop rotation, after 20 years of modelled SOC changes. This study shows that an intervention management has substantially lower GHG emissions compared to the conventional scenario. Much of the total difference between scenarios is attributed to the difference in SOC changes, which are positive in the intervention scenario and negative in the conventional. Soil N2O emissions were high in both scenarios but were lower in the intervention scenario because of lower inorganic fertiliser application. However, the method for assessing soil N2O emissions produces rougher estimations than the method for SOC changes, and the full effects of management on N2O emissions has not been quantified in this study. Higher SOC in the intervention scenario also resulted in lower N input and higher yields, causing lower emissions per functional unit. Lower GHG emissions resulted also from replacing inorganic fertiliser with manure and reducing tillage. In conclusion, intervention agriculture is shown to perform substiantially better than conventional in terms of GHG emissions, but further research should investigare uncertainties in the result.