Alan Rotz, USDA/ARS, Pasture Systems and Watershed Management Research Unit, University Park, PA.


Dairy farms, along with other animal feeding operations, were asked this past year to consider a consent agreement with the U.S. Environmental Protection Agency (EPA) to fund research into whether or not air pollution laws apply to farms. For dairy operations, the major pollutant of concern is ammonia. The Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) and the Emergency Planning and Community Right-To-Know Act (EPCRA) require anyone to immediately notify the National Response Center and other emergency planners if more than 100 pounds of ammonia have been released within any 24-hour period. There are large penalties for failure to comply with these laws.

Although ammonia is also released following manure application to the field and during grazing, EPA’s primary concern at this time is ammonia coming from barns and manure storages. Their current focus is also on maximum daily emissions rather than long-term average emissions. Objective: To estimate typical ammonia emission rates from Pennsylvania dairy farms to determine farm sizes that might emit more than 100 pounds on any day of the year.


A process level model was used to predict daily emissions of ammonia from dairy facilities over many years of Pennsylvania weather. Farm types included tie stall and free stall barns with and without long-term manure storages. Storages included top-loaded tanks and ponds and bottom-loaded tanks where a crust formed that reduced ammonia emissions. Grazing farms were also simulated where emissions were reduced because animals were not in the barn during the warmest part of the year when ammonia emissions tend to be the greatest.


Ammonia emission levels vary considerably among farms due to differences in barn design, manure handling practices, and other feeding and management strategies. For a free stall barn with a toploaded manure pit, the emission rate on a hot summer day may be as high as 1 pound per cow per day. By using a bottom-loaded slurry tank where a crust forms on the surface, this maximum emission can be reduced 20 percent. Eliminating the manure storage through daily hauling can reduce this emission by over 40 percent. Compared to a free stall barn, a tie stall barn with daily hauling can also reduce this maximum emission rate by about 30 percent.

Use of grazing can also greatly reduce the maximum ammonia emission. Since grazing animals are outside during the warmest part of the year, the maximum emission from the barn occurs under cooler weather. Therefore, the use of grazing reduces the maximum emission by about 50 percent. Based upon these emission rates, we can estimate farm sizes that could emit over 100 pounds of ammonia during any day of the year. For a free stall barn with a top-loaded manure storage, farms with as few as 100 cows and their replacement heifers could fall under regulation.

Since most tie stall barns in use today are on relatively small farms, this type of farm would normally not be a concern. Grazing farms are also unlikely to be included with farms that emit 100 pounds of ammonia per day. On grazing operations though of over 200 cows where animals are confined in a free stall barn for a major portion of the year and a manure storage is used, this limit still may be exceeded. As farm sizes continue to grow, technological changes appear to be needed to reduce ammonia formation and emission from our dairy farms.