Nitrous oxide emissions from a drained peatland area (D site) and a drained and mineral soil-dressed (D-SD site) peatland area in central Hokkaido Island, northern Japan were measured. Nitrous oxide flux at the D-SD site was -0.01-1.15 mgN m -2 hr -1 , showing a sudden increase during the period June-October. Nitrous oxide flux at the D site was -0.01-4.47 mgN m -2 hr -1 , showing much higher fluxes (0.40-4.47 mgN m -2 hr -1 ) during July-October 2004 than other monitoring periods (0.30 mgN m

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... hr -1 maximum flux). The nitrous oxide concentration in the soil rose remarkably concomitantly with the nitrous oxide flux in 2004. These fluxes were much higher than those measured in an undeveloped mire near this study site. Annual nitrous oxide emissions at the D and D-SD site were 3.8-41.7 kgN ha -1 yr -1 ; which were far larger than in the above-described undeveloped mire (0.3 kgN ha -1 yr -1 ). The results of this study showed that the conversion of peatland into agricultural land with drainage and soil dressing changed their atmospheric impact dramatically. Nitrous oxide concentrations of soil gas were higher at the D site than at the D-SD site, particularly during 2004. High nitrous oxide concentrations in the soil gas corresponded to dramatically high nitrous oxide fluxes at the D site in 2004, while the precipitation surplus was also more than the other two years in 2004. Our results suggest that the peatland drainage contributes to increased nitrous oxide generation and that an interannual change of nitrous oxide emissions occurs with climate conditions.