SEASONAL-VARIATIONS IN DENITRIFICATION AND NITROUS-OXIDE EVOLUTION ATTHE LANDSCAPE SCALE

This study was conducted to examine the seasonal and spatial variabili ty of denitrification in various landform elements in a pea (Pisum sat ivum 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. Consequen tly, ordinary statistical procedures (i.e., those based on a normal di stribution) were considered inappropriate for this study, and nonparam etric statistics were used to describe the data. Denitrification activ ity and N2O evolution exhibited similar temporal and landscape-scale p atterns and were highly correlated, suggesting that denitrification wa s the main source of N2O evolution. In general, N2O evolution accounte d for almost-equal-to 41% of the denitrification activity. Maximum rat es of denitrification were low prior to spring tillage and seeding, in creased during the first half of the growing season (following the add ition of fertilizer N), and decreased toward the end of the growing se ason; denitrification had essentially ceased by the fall sampling. Sta tistical outliers for denitrification activity, i.e., hotspots of acti vity, occurred predominantly at low levels of denitrification activity and were completely absent when denitrification activity was at its m aximum. Therefore, the importance of hotspots of activity for estimati ng seasonal rates of denitrification appears to be limited. Soil water content was the most dominant factor controlling denitrification acti vity, followed by the concentration of NH4+, total soil respiration, a nd NO3-. The intensity of denitrification was controlled largely by hy drologic processes, which, in turn, were influenced by the topography of the landscape. Nevertheless, the landscape-scale patterns of denitr ification and N2O evolution were intensity-independent and remained co nsistent throughout the season.