Seasonal Variations in Denitrification and Nitrous Oxide Evolution at the Landscape Scale
- C. van Kessel ,
- D. J. Pennock and
- R. E. Farrell
This study was conducted to examine the seasonal and spatial variability of denitrification in various landform elements in a pea (Pisum sativum L.) field at Blaine Lake, Saskatchewan, Canada. The distributions of denitrification activity and N2O evolution were highly skewed, and could not be log-transformed to yield normal distributions. Consequently, ordinary statistical procedures (i.e., those based on a normal distribution) were considered inappropriate for this study, and nonparametric statistics were used to describe the data. Denitrification activity and N2O evolution exhibited similar temporal and landscape-scale patterns and were highly correlated, suggesting that denitrification was the main source of N2O evolution. In general, N2O evolution accounted for ≅41% of the denitrification activity. Maximum rates of denitrification were low prior to spring tillage and seeding, increased during the first half of the growing season (following the addition of fertilizer N), and decreased toward the end of the growing season; denitrification had essentially ceased by the fall sampling. Statistical outliers for denitrification activity, i.e., hotspots of activity, occurred predominantly at low levels of denitrification activity and were completely absent when denitrification activity was at its maximum. Therefore, the importance of hotspots of activity for estimating seasonal rates of denitrification appears to be limited. Soil water content was the most dominant factor controlling denitrification activity, followed by the concentration of NH+4, total soil respiration, and NO−3. The intensity of denitrification was controlled largely by hydrologic processes, which, in turn, were influenced by the topography of the landscape. Nevertheless, the landscape-scale patterns of denitrification and N2O evolution were intensity-independent and remained consistent throughout the season.
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