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Title: SEASONAL AND SPATIAL VARIATIONS OF DENITRIFYING ENZYME ACTIVITY IN FEEDLOT SOIL

Author
item Woodbury, Bryan
item Miller, Daniel
item Nienaber, John
item Eigenberg, Roger

Submitted to: Transactions of the ASAE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/24/2001
Publication Date: 12/31/2001
Citation: Woodbury, B.L., Miller, D.N., Nienaber, J.A., Eigenberg, R.A. 2001. Seasonal and spatial variations of denitrifying enzyme activity in feedlot soil. Transactions of the ASAE 44(6):1635-1642. 2001.

Interpretive Summary: Nitrogen is lost from the feedlot by many pathways. A major pathway is ammonia gas lost to the atmosphere and can account for much of the lost nitrogen. However, another important pathway is the conversion to nitrogen gas by bacteria, which has not been widely studied. The object of this paper was to study the seasonal loss of nitrogen gas from a feedlot soil. Electrical conductivity was used to identify locations within the pen to represent microbial activity. Various depths were analyzed for microbial activity and nutrient concentrations. Microbial activity varied greatly according to season, depth, and location within the pen. The surface soil maintained the highest level of microbial activity when compared to the other soil depths, even when the soil temperatures were near freezing. Below the 4 inch depth microbial activity was near zero. We conclude that environmental conditions control microbial conversion of nitrate to nitrogen gas.

Technical Abstract: 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, 0 - 0.10 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/hr based on season, depth, and spacial 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. Downgradient surface materials maintained DEA levels greater than 60 mmol/g/hr even when soil temperatures were near freezing. 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.