Including trace gas fluxes in estimates of the carbon mitigation potential of UK agricultural land

Abstract. A number of changes in agricultural land‐management show some potential as carbon mitigation options. However, research has focused on CO 2 ‐carbon mitigation and has largely ignored potential effects of land management change on trace gas fluxes. In this paper, we attempt for the first time, to assess the impact of these changes on fluxes of the important agricultural greenhouse gases, methane and nitrous oxide, in the UK. The estimates presented here are based on limited evidence and have a great (unquantifiable) uncertainty associated with them, but they show that the relative importance of trace gas fluxes varies enormously among the scenarlos. In some, such as the application of sewage sludge, woodland regeneration and bioenergy production scenarios, the inclusion of estimates for trace gas fluxes makes only a small (<10%) difference to the CO 2 ‐C mitigation potential. In the animal manure and agricultural extensification scenarios, including estimates of trace gas fluxes has a large impact, increasing the CO 2 ‐C mitigation potential by up to 50%. In the no‐till scenario, the carbon mitigation potential decreases significantly due to a sharp increase in N 2 O emissions under no‐till. When these land‐management options are combined for the whole agricultural land area of the UK, including trace gases has an impact on estimated mitigation potentials, and depending upon assumptions for the animal manure scenario, the total mitigation potential either decreases by about 10% or increases by about 30%, potentially shifting the mitigation potential of the scenario closer to the EU's 8% Kyoto target for reduction of CO 2 ‐carbon emissions (12.52 Tg C yr −1 for the UK).