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.
