Micrometeorological N2O Fluxes Linked to Conditions in the Soil Profile during Winter and Spring Thaw.
Claudia Wagner-Riddle, University of Guelph, Dept. of Land Resource Science, Guelph, ON N1G 2W1, Canada
Advances in analytical techniques for nitrous oxide concentration measurements over the last 15 years have enabled the use of micrometeorological methods for measurement of N2O fluxes. These methods are ideally suited for spatial integration, and for the study of temporal variability of fluxes. Year-round measurement of N2O fluxes using the flux-gradient method over 2000 to 2005 showed that winter and spring thaw emissions are affected by soil management practices. During years with cold winters (eg. 2003, mean monthly air temperature for Jan and Feb <-9°C), no-tillage plots had a deeper snow cover, and a shallower freezing depth compared to plowed plots. Nitrous oxide fluxes were highest from the tilled plots during years with cold winters. During mild winters (eg. 2002), differences in soil management did not result in different physical conditions in the soil profile, and correspondingly, N2O fluxes were also not different between treatments. Soil gas samples taken from different depths showed nitrous oxide build-up in the profile when some thawing occurred but not in frozen soil. The surface flux measured with independent methods (micrometeorological and chambers) showed that the increase in emission at spring thaw was triggered when a small fraction of the soil profile had thawed, and lasted until thawing concluded in the profile. This indicates that the burst in flux at spring thaw was mostly due to N2O produced during thawing.