Submitted to: Meeting Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 12/23/2004
Publication Date: 1/5/2005
Citation: Todd, R.W., Cole, N.A., Harper, L.A., Flesch, T.K., Baak, B.H. 2005. Ammonia and gaseous nitrogen emissions from a commercial beef cattle feedyard estimated using the flux-gradient method and N:P ratio analysis. In: State of the Science Animal Manure and Waste Management, January 4-7, 2005, San Antonio, Texas. 2005 CDROM. Interpretive Summary: Ammonia is a potential polluter of the atmosphere and ecosystems. The nitrogen in feed is the source of ammonia from animal feeding operations. So, knowing how much ammonia is emitted from feeding operations is a priority research issue. Micrometeorological methods are advantageous to quantify ammonia emissions because they don't interfere with the processes that control emissions from animal feeding operations. We used the flux-gradient method to estimate ammonia emissions from beef cattle feedyard pens, and compared it to loss of all forms of gaseous nitrogen estimated from the change in the nitrogen:phosphorus ratio of feed and manure. At a commercial feedyard on the High Plains of the Texas Panhandle, ammonia in the air, wind speed, and air temperature were measured on towers erected in the feedyard. Gaseous nitrogen loss was estimated by collecting and analyzing feed and manure samples for nitrogen and phosphorus, and using diet composition, amount of feed fed, head count, and cattle weights. Ammonia emissions were 55% of the nitrogen fed to cattle in summer and 27% in winter. Gaseous nitrogen loss averaged 45% of fed nitrogen, so that almost all nitrogen was lost as ammonia during summer. Ammonia comprised about 60% of gaseous nitrogen loss during winter. These results will help producers, researches and regulators understand the magnitude of ammonia emissions, and how they can be quantified.
Technical Abstract: Micrometeorological methods used to estimate emissions are advantageous because they are noninterfering and can integrate fluxes over large areas. They have not been routinely applied to beef cattle feedyards, where physical complexity and the possibility of disturbed air flow may be problematic. Our objective was to use the flux-gradient method to estimate NH3 emissions from beef cattle feedyard pens, and compare it to gaseous N loss inferred from analysis of the change in feed and manure N:P ratio. Research was conducted at a commercial feedyard on the High Plains of the Texas Panhandle, during three summer and two winter campaigns, 2002-2004. Profiles of NH3 concentration, wind speed, and air temperature were measured on 6-m or 10-m towers erected in the feedyard. Ammonia concentration was measured using acid gas washing or chemiluminescence, and NH3 flux estimated using gradient or finite difference forms of the flux-gradient method. Gaseous N loss was estimated by collecting and analyzing feed and pen surface manure samples for N and P, and using inputs including diet composition, feed fed, head count, and cattle weights. Summer mean daily NH3 flux ranged from 55 to 93 ug/m^2/s, averaging 70 ug/m^2/s. Winter NH3 flux was half that of summer. Ammonia-N emission rate averaged 4650 kg/d (55% of fed N) during summer and 2140 kg/d (27% of fed N) during winter. Gaseous N loss averaged 45% of fed N, so that most N was lost as NH3 during summer, and NH3 comprised about 60% of gaseous N loss during winter. Ammonia emission factor for this feedyard was 15 kg/head/yr, with 50% of fed N lost as ammonia.