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

A number of changes in agricultural land-management show some potential as carbon mitigation options. However, research has focused on CO2-carbon miti gation and has largely ignored potential effects of land management change on trace gas fluxes. In this paper, me attempt for the first time, to asses s the impact of these changes on fluxes of the important agricultural green house gases, methane and nitrous oxide, in the UK. The estimates presented here are based on limited evidence and have a great (unquantifiable) uncert ainty associated with them, but they show that the relative importance of t race gas fluxes varies enormously among the scenarios. In some, such as the application of sewage sludge, woodland regeneration and bioenergy producti on scenarios, the inclusion of estimates for trace gas fluxes makes only a small(<10%) difference to the CO2-C mitigation potential. In the animal man ure and agricultural extensification scenarios, including estimates of trac e gas fluxes has a large impact, increasing the CO2-C mitigation potential by up to 50%. In the no-till scenario, the carbon mitigation potential decr eases significantly due to a sharp increase in N2O 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 mitig ation potentials, and depending upon assumptions for the animal manure scen ario, the total mitigation potential either decreases by about 10% or incre ases by about 30%, potentially shifting the mitigation potential of the sce nario closer to the EU's 8% Kyoto target for reduction of CO2-carbon emissi ons(12.52 Tg Cyr(-1) for the UK).