Impacts of land management on fluxes of trace greenhouse gases

Abstract. Land use change and land management practices affect the net emissions of the trace gases methane (CH₄) and nitrous oxide (N₂O), as well as carbon sources and sinks. Changes in CH₄ and N₂O emissions can substantially alter the overall greenhouse gas balance of a system. Drainage of peatlands for agriculture or forestry generally increases N₂O emission as well as that of CO₂, but also decreases CH₄ emission. Intermittent drainage or late flooding of rice paddies can greatly diminish the seasonal emission of CH₄ compared with continuous flooding. Changes in N₂O emissions following land use change from forest or grassland to agriculture vary between climatic zones, and the net impact varies with time. In many soils, the increase in carbon sequestration by adopting no-till systems may be largely negated by associated increases in N₂O emission. The promotion of carbon credits for the no-till system before we have better quantification of its net greenhouse gas balance is naïve. Applying nitrogen fertilizers to forests could increase the forest carbon sink, but may be accompanied by a net increase in N₂O; conversely, adding lime to acid forest soils can decrease the N₂O emission.