Submitted to: Hoard's Dairyman
Publication Type: Trade Journal
Publication Acceptance Date: May 4, 2005
Publication Date: May 25, 2005
Citation: Rotz, C.A. 2005. How much ammonia do dairy farms emit? Hoard's Dairyman. 150(10):371. Technical Abstract: Dairy farms, along with other animal feeding operations, are being asked 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. The major concern is ammonia emission with a maximum limit of 100 pounds released within any 24-hour period. Because of the expense and difficulty in making reliable measurements, few actual farm measurements have been made. As another option, process-based models developed from sound science can give an estimate of the amount of ammonia being emitted by our farms. Although ammonia is emitted following field application of manure and during grazing, the EPA’s focus at this time is on that coming from barns, manure storages, and feedlots. 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 top-loaded manure pit, the emission on a hot summer day may be about one pound per cow per day. Use of a bottom-loaded slurry tank can reduce this maximum emission 20%, and eliminating the manure storage through daily hauling can reduce emissions an additional 30%. Since grazing animals are outside during the warmest part of the year, the use of grazing reduces the maximum emission by about 50%. Daily ammonia emissions from feedlots can be high, near one pound per cow. Based upon these emission rates, farm sizes can be estimated that may emit over 100 pounds of ammonia during any day of the year. For a free stall barn and top-loaded manure storage, this farm size is around 100 cows. For farms using an open feedlot or a free stall barn and bottom-loaded slurry storage, the size limit is just a little greater. Since most tie stall barns in use today are on relatively small farms, the low emission from this type of farm would normally not reach this level. Grazing farms with around 200 cows or less should also not be included with farms that emit 100 pounds of ammonia per day. Until more actual farm measurements of ammonia emissions can be made, model predicted emission rates provide an estimate of the type and size of farms that may be affected by regulations that seek to maintain ammonia emissions from the barn and manure storage to less than 100 pounds per day. As farm sizes continue to grow, technological changes appear to be needed to reduce ammonia formation and emission from our dairies.