Fluxes of N2O from farmed peat soils in Finland

Agricultural peat soils are important sources of nitrous oxide (N2O). Emissions of N2O were measured from field plots of grass, barley, potatoes and fallow on a peat field in northern Finland during 2000-2002 and in southern Finland in 1999-2002. In the north the mean annual fluxes of N2O (with their standard errors) during 2 years were 4.0 (+/-1.2), 13 (+/-3.0) and 4.4 (+/-0.8) kg N ha(-1) from the plots of grass, barley and fallow, respectively. In the north there were no significant thaw periods in the middle of winter. As a result, the thawing in the spring did not induce especially large N2O emissions. Emissions of N2O were larger in the south than in the north. In the southern peat field the mean annual fluxes during 3 years were 7.3 (+/-1.2), 15 (+/-2.6), 10 (+/-1.9) and 25 (+/-6.9) kg N2O-N ha(-1) for grass, barley, potato and fallow plots, respectively. Here, the largest single episodes of emission occurred during the spring thaw each year, following winter thaw events. An emission factor of 10.4 kg N2O-N ha(-1) year(-1) for the N2O emission from the decomposition of the peat results from these data if the effect of fertilization according to the IPCC default emission factor is omitted. The direct effect of adding N as fertilizer on N2O emissions was of minor importance. On average, 52% of the annual N2O flux entered the atmosphere outside the cropping season (October-April) in the north and 55% in the south. The larger N2O fluxes from the peat soil in the south might be due to the more humified status of the peat, more rapid mineralization and weather with more cycles of freezing and thawing in the winter.