Nitrous oxide from beef cattle feedyards: Understanding effects of microbial community structure, climate and manure properties on denitrification

Authors: Waldrip, Heidi; Parker, David; Miller, Sierra; Miller, Daniel; Durso, Lisa; CASEY, KENNETH - Texas A&M Agrilife; Todd, Richard; CORTUS, ERIN - University Of Minnesota

Submitted to: ASABE Annual International Meeting
Publication Type: Abstract Only
Publication Acceptance Date: 2/6/2018
Publication Date: 8/1/2018
Citation: Waldrip, H., Parker, D.B., Miller, S., Miller, D.N., Durso, L.M., Casey, K., Todd, R.W., Cortus, E. 2018 [abstract]. Nitrous oxide from beef cattle feedyards: Understanding effects of microbial community structure, climate and manure properties on denitrification. ASABE Annual International Meeting. Paper #1801295.

Interpretive Summary:

Technical Abstract: Nitrous oxide is a potent greenhouse gas that is emitted from accumulated manure in beef cattle feedyard pens. Recent research has greatly advanced our understanding of the magnitude of nitrous oxide emissions from feedyards; however, the primary mechanism by which it is produced (i.e., nitrification, denitrification, coupled nitrification-denitrification, etc.) remains unclear. Effective mitigation of feedyard nitrous oxide via manure management, addition of inhibitors, or other chemical or organic compounds requires a detailed understanding of nitrous oxide formation under varying conditions. Temperature and water content are primary factors affecting nitrous oxide emissions from manure. The objective of this research was to determine how temperature and water content affects potential denitrification enzyme activity (DEA), nitrification activity (NA), and microbial community structure following rainfall. A recirculating-flow-through, non-steady-state (RFT-NSS) chamber system monitored nitrous oxide emissions from manure following two 25.4 mm rainfall events, with drying time between events. Manures were kept in large chambers at temperatures of 5.0, 11.2, 17.2, 21.5, 26.8, 31.0, 38.1, and 46.2 degrees C. Samples were collected at depths of 0-5 cm and 5-10 cm immediately after rainfall events and at intervals during the 29 day study. These were analyzed for potential DEA using an Ankom Gas Production System, where manure was incubated under anaerobic conditions with high levels of nitrate and glucose. Nitrification activity was determined on aerobic samples incubated with excess ammonium. Enzyme activities were expressed as rate of nitrate disappearance (DEA) or appearance (NA) over time. In addition, microbial community structure at different depths and over time was analyzed via 16s DNA sequencing. These data were regressed against measured nitrous oxide emissions, manure physicochemical properties (i.e., pH, redox status, and ammonium/ammonia, nitrite/nitrate and total nitrogen and carbon concentrations). This allowed us to evaluate how temperature, water content, and the microbial population affect potential denitrification and nitrification rates. These data illumated major factors and interactions involved in nitrous oxide flux. For example, nitrous oxide flux was positively related to temperature (P=0.002), ammonia (P<0.001), and nitrate (P< 0.001) in the top 5 cm of manure. There were strong negative relations between nitrous oxide and dry matter (P<0.0001), NA (P=0.003), redox status (P=0.003), and pH (P=0.004). The proportion of Firmicutes and Actinobacteria decreased with incubation temperature and over time, while Proteobacteria and Chloroflexi tended to increase. Data analyses are ongoing; however, information derived from this study will be useful for developing targeted mitigation plans that reduce greenhouse gas emissions from commercial beef feedyards on the Southern High Plains.