Seasonal fluctuations of N2O emission in different soil landscape systems
van Kessel, C.
Nitrous oxide has been widely recognized as a major scientific and environmental ‘issue because of its involvement in global warming and destruction of the atmospheric ozone layer. The inherently high temporal and spatial variabilities of N2O emission has hindered attempts to establish predictive relationships with its controlling variables. Hence achieving annual estimates for N2O emission at a large scale continues to pose a challenge for researchers. As a pre-requisite to quantify annual N2O emissions at a regional scale, this study was conducted to determine the landscape- and seasonal-scale patterns of N2O emission. Nitrous oxide emissions were assessed in six soil landscape systems chosen as representative units of a delineated region in the Black Soil Zone. The region is stratified into three main textural groups, within which different land uses were selected: clay loam (fertilized wheat and pasture sites), fine sandy loam (fertilized canola site), and sandy (fertilized oat, alfalfa, and forest sites). A systematic grid design was employed at each site and N2O emission was monitored using a sealed chamber method. A clear landscape-scale pattern of N2O emission was observed; lower landscape positions showed higher N2O flux than the upper landscape positions. This pattern remained consistent throughout the season, with N2O fluxes increasing towards the early summer, decreasing towards the late summer, and virtually ceasing by the onset of frost (fall). A considerable pulse of activity was also observed during the early spring (March and April). This indicates the importance of an appropriate temporal sampling scheme that would account for this spring activity in order to achieve a more reliable annual estimate of N2O emission. In any model used for large-scale and long-term estimates of flux, it is therefore necessary to reflect not only the landscape variability but also the seasonal variability of N2O emission.
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