Greenhouse Gas and Ammonia Emissions from an Open-Freestall Dairy in Southern Idaho

Concentrated dairy operations emit trace gases such as ammonia (NH3), methane (CH4), and nitrous oxide (N2O) to the atmosphere. The implementation of air quality regulations in livestock-producing states increases the need for accurate on-farm determination of emission rates. Our objective was to determine the emission rates of NH3, CH4, and N2O from the open-freestall and wastewater pond source areas on a commercial dairy in southern Idaho using a flush system with anaerobic digestion. Gas concentrations and wind statistics were measured and used with an inverse dispersion model to calculate emission rates. Average emissions per cow per day from the open-freestall source area were 0.08 kg NH3, 0.41 kg CH4, and 0.02 kg N2O. Average emissions from the wastewater ponds (g m(-2) d(-1)) were 6.8 NH3, 22 CH4, and 0.2 N2O. The combined emissions on a per cow per day basis from the open-freestall and wastewater pond areas averaged 0.20 kg NH3 and 0.75 kg CH4. Combined N2O emissions were not calculated due to limited available data. The wastewater ponds were the greatest source of total farm NH3 emissions (67%) in spring and summer. The emissions of CH4 were approximately equal from the two source areas in spring and summer. During the late fall and winter months, the open-freestall area constituted the greatest source area of NH3 and CH4 emissions. Data from this study can be used to develop trace gas emissions factors from open-freestall dairies in southern Idaho and other open-freestall production systems in similar climatic regions.