Temporal denitrification at the landscape scale in a Black soil
van Kessel, C.
Landscape scale and seasonal pattern of denitrification activity have to be incorporated in a model to estimate total N losses. A study was conducted to exam the seasonal variability of denitrification in a landscape near Blaine Lake, Saskatchewan. A 120 x 120 m sampling grid, separated by a spacing of 10 m, was established in a Black Chernozem soil. The area was surveyed, landform elements identified and from each landform element ten sampling points were further selected and sampled throughout the season for denitrification activity by the acetylene-blockage approach. Soils samples were taken seven times during the entire 1991 season before the area was prepared for seeding in the spring, following precipitation events during the growing season , and in the fall at the onset of frost. Following incubation, soil samples were analyzed for percent moisture, NH4+ and NO3-, soluble organic carbons, and total soil respiration. The distribution of denitrification activities were highly skewed and followed a distinct landscape pattern that remained consistent throughout the year. Denitrification activity increased significantly after the occurrence of a precipitation event and was further enhanced after the application of fertilizer-N, ceased toward the end of the growing season and became zero at the fall sampling. Moisture was the most dominant parameter controlling denitrification activity followed by the concentration of and NH4+ and NO3-. The highest denitrification activity occurred on the divergent and convergent footslopes, the lowest activity on the divergent shoulder and upper level landform elements, a landscape scale pattern that remained consistent throughout the year, independent of the magnitude of activity. Ambient evolution of N2O and denitrification activity followed predominantly a similar temporal and landscape scale pattern. By estimating the duration of a denitrification following a precipitation event at the various landform elements and correcting for the percentage each landform element occupies in the landscape, the total denitrification per precipitation during the early part of the season was estimated at 357 g N ha-1 cycle-1. In conclusion, results indicates that landscape scale pattern of denitrification remained constant throughout the growing season and was predominantly induced by precipitation events.
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