This project proposal will make use of a novel laser technology to analyze N2O isotopic composition at ambient levels. A recent study on arable organic soils has shown extremely high emissions of the potent greenhouse gas N2O that were only partly explained by management. Site-specific conditions were proposed to influence N cycling, such as fluctuating groundwater table and acid sulphate soil, possibly involving pyrite. Central to this project are targeted field campaigns to monitor gas fluxes using automated chambers, soil gas sampling, and biogeochemical characterization of soil profiles. From concentrations and isotopomer composition of N2O emitted, and in soil gas sampled to 1 m depth, we aim to identify zones of N2O production and reduction, and relative contributions of nitrification and denitrification processes. Specific hypotheses involving the regulation of N2O production are tested in lab experiments. Results will support GHG mitigation efforts for organic soils.