Measuring N2O emissions from organic soils by closed chamber or soil/snow N2O gradient methods

Drained organic soils contribute substantial amounts of nitrous oxide to the global atmosphere, and we should be able to estimate this contribution. We have investigated when the fluxes of N2O from drained forested or cultivated organic soils could be determined by calculating the fluxes from the concentration gradients of the gas in soil or snow according to Fick's law of diffusion. A static chamber method was applied as a control technique for the gas gradient method. Concentrations of N2O in soil varied from 296 nl l(-1) to 8534 nl l(-1) during the snow-free periods and were greatest in the early summer. Our results suggest that the gas gradient method can be used to estimate N2O emissions from drained organic soils. There was some systematic difference in the N2O fluxes measured with these two methods, which we attributed to the differences in weather between years 1996 and 1997. In the wet summer of 1996 the chamber method gave greater flux rates than the gas gradient method, and the reverse was true in the dry summer of 1997. In the forest the N2O fluxes measured with the two methods agreed well. The gas gradient is convenient and fast for measuring N2O emissions from fairly dry organic unfrozen soil. In winter the diffusion calculation based on the N2O gradients in snow and the chamber method gave fairly similar flux rates and provided adequate estimates of the fluxes of N2O in winter.