Seasonal and Spati Al Variations of Denitrifying Enzyme Activity in Feedlot Soil

Animal waste models, used by producers to apply best management practices for waste control, are only crudeapproximations for nitrogen lost from the feedlot. Ammonia loss has been widely studied and accounts for the majority ofgaseous nitrogen lost from a feedlot soil; however, denitrification has not been thoroughly investigated. The objectives of thisstudy were to determine the seasonal denitrification enzyme activity (DEA) of a feedlot soil and evaluate potential controllingmechanisms. Electromagnetic mapping techniques were used to identify three locations within the feedlot pen. Three depths(unconsolidated surface material, 00.10 m, 0.100.20 m) were isolated at each location and analyzed for DEA, nitrificationactivity, denitrifier most probable number, soil moisture, pH, volatile solids, total carbon, and total nitrogen. Denitrificationenzyme activity varied from 0.0 to 132.2 mmol gsoil 1 hr 1 based on season, depth, and spatial location. However, no singlefactor was perfectly correlated with DEA across all locations and depths. The seasonal average DEA of the unconsolidatedsurface material maintained significantly higher levels when compared to other depths. Downgradient surface materialsmaintained DEA levels greater than 60 mmol gsoil 1 hr 1 even when soil temperatures were near 0C. Also, the seasonalaverage DEA below 0.10 m for all locations was near zero during the entire investigation, significantly less than the otherdepths. We conclude that a range of environmental factors, alone or in conjunction, influence DEA depending upon locationwithin the pen and soil depth.