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 compare the emission rates of NH3, CH4, and N2O from three commercial dairies in southern Idaho that vary in size, animal housing, and manure handling systems. The three dairies consisted of a small open lot dairy (700 cows), large open lot dairy (10,000 cows) and a large open-freestall dairy (10,000 cows) with an anaerobic digester. Both housing and manure management systems were monitored in order to determine “whole farm emissions” and determine the effects of manure handling practices on emissions from the different farm sectors. Gas concentrations and wind statistics were measured and used with an inverse dispersion model to calculate emission rates. Average emissions from the housing area per cow per day for the three farms ranged from 0.10 – 0.14 kg NH3, 0.33-0.49 kg CH4 and 0.01 - 0.02 kg N2O. Average emissions from the wastewater ponds (g cow-1 d-1) were 10 - 129 NH3, 27 – 1,028 CH4 and 3.7 – 4.9 N2O. Data from this study can be used to develop trace gas emissions factors from dairies in southern Idaho and other production systems in similar climatic regions.
Cows at an open-lot dairy.
Approximately 34 percent of the total U.S. population of milk cows is located in the semi-arid to arid western U.S., with California and Idaho being two of the top four dairy-producing states. Dairy production in this region is dominated by concentrated feeding operations with the majority of milk cows being located on dairy farms with more than 2,500 cows. The impact of these production systems on regional air quality and potential impacts on climate change via greenhouse gas (GHG) emissions has become a concern. Dairy farms emit trace gases such as ammonia (NH3), methane (CH4) and nitrous oxide (N2O) to the atmosphere. While NH3 is a precursor to fine particulate matter that can affect livestock and human health as well as air quality, CH4 and N2O are potent GHGs. To date there is limited on-farm emissions data from dairy production facilities that covers the range of trace gases that are important from a regulatory and environmental standpoint. Particularly there is a lack of information from dairy cattle production systems typical of the semi-arid western region that captures both the diurnal and seasonal variation in emissions. Therefore, the objective of our research has been to determine the emission rates of NH3, CH4 and N2O over the course of a year from various source areas (animal housing and manure management systems) on open-lot and open-freestall dairies located in southern Idaho to determine both diurnal and seasonal trends in emissions.
Emissions of NH3, CH4 and N2O were estimated from three commercial dairies consisting of a small open lot dairy (700 cows), large open lot dairy (10,000 cows) and a large open-freestall dairy (10,000 cows). Emissions were determined utilizing inverse dispersion modeling at the housing and manure storage areas of the production facilities. Hourly emission rates were evaluated to determine trends in emissions over time. Annual emissions estimates were determined for the systems as well as an evaluation of the areas within the facility that contributed the greatest amount of emissions to the farm total.
Wastewater pond at an open-freestall dairy.
There were strong diurnal trends in the emission of NH3 and CH4 at all locations studied, while there were only diurnal trends in N2O emissions at the wastewater ponds. Emissions tended to be lower in the late evening and early morning and then increased throughout the day as temperature, wind speed, and animal activity increased. There was some seasonal variation in NH3 and CH4, particularly at the wastewater ponds. In fact there was a linear increase in emissions with increasing temperature at the wastewater ponds for both NH3 and CH4. However, N2O emissions from the wastewater ponds tended to be greatest in spring. Ammonia emissions from the animal housing areas tended to be the least in winter and greatest when temperatures were increasing and lot conditions were wetter. Annual average emissions from the housing area per cow per day for the three farms ranged from 0.10 – 0.14 kg NH3, 0.33-0.49 kg CH4 and 0.01 - 0.02 kg N2O. Annual average emissions from the wastewater ponds (g cow-1 d-1) were 10 - 129 NH3, 27 – 1,028 CH4 and 3.7 – 4.9 N2O. Annual average emissions measured at the compost yard of one open lot dairy were 17 g NH3, 148 g CH4, and 9.3 g N2O (g cow-1 d-1). The annual average combined emissions of NH3 and CH4 from cattle housing and manure storage ranged from 0.13 to 0.22 kg NH3 cow-1 d-1 and 0.32 to 1.4 kg CH4 cow-1 d-1. At the open lot dairies, the lot areas had the greatest contribution to emissions of NH3 and N2O year round while CH4 emissions were greatest from the lots in the winter and spring, but once temperatures increased, the lagoon became the largest source of CH4 emissions for the remainder of the year. At the open freestall dairy, the wastewater ponds were the greatest source of total farm NH3 emissions from spring through fall while the emissions of CH4 were approximately equal from the two source areas during this time period. In the winter months, due to decreasing temperatures and freezing of the pond surfaces, the open-freestall source area constituted the greatest source area of both NH3 and CH4 emissions.
Open freestall dairy.
Present and future research is focused on developing better ways to estimate emissions from wastewater ponds and manure storage areas based on physical and chemical characteristics of the source combined with meteorological conditions. We are also working to validate and improve process based models can be used to estimate emissions from dairy production systems as well as identify management strategies to reduce on-farm emissions.
April Leytem, Research Soil Scientist, USDA-ARS firstname.lastname@example.org
Dr. Robert Dungan, Research Microbiologist, USDA-ARS
Dr. Dave Bjorneberg, Agricultural Engineer, USDA-ARS
A portion of this work was funded by The Independent Dairy Environmental Action League LLC (IDEAL).
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