Animal waste models, used by producers to apply best management practices for waste control, are only crude approximations for nitrogen lost from the feedlot. Ammonia loss has been widely studied and accounts for the majority of gaseous nitrogen lost from a feedlot soil; however, denitrification has not been thoroughly investigated. The objectives of this study were to determine the seasonal denitrification enzyme activity (DEA) of a feedlot soil and evaluate potential controlling mechanisms. Electromagnetic mapping techniques were used to identify three locations within the feedlot pen. Three depths (unconsolidated surface material, 00.10 m, 0.10-0.20 m) were isolated at each location and analyzed for DEA, nitrification activity, denitrifier most probable number, soil moisture, pH, volatile solids, total carbon, and total nitrogen. Denitrification enzyme activity varied from 0.0 to 132.2 mmol (g{sub}(soil)){sup}(-1) hr{sup}(-1) based on season, depth, and spatial location. However, no single factor was perfectly correlated with DEA across all locations and depths. The seasonal average DEA of the unconsolidated surface material maintained significantly higher levels when compared to other depths. Down gradient surface materials maintained DEA levels greater than 60 mmol (g{sub}(soil)){sup}(-1) hr{sup}(-1) even when soil temperatures were near 0℃. Also, the seasonal average DEA below 0.10 m for all locations was near zero during the entire investigation, significantly less than the other depths. We conclude that a range of environmental factors, alone or in conjunction, influence DEA depending upon location within the pen and soil depth.
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