Title: Ammonia emissions from cattle feeding operations. Authors
Submitted to: Extension Publications
Publication Type: Experiment Station
Publication Acceptance Date: June 15, 2012
Publication Date: December 15, 2012
Citation: Preece, S.L., Cole, N.A., Todd, R.W., Auvermann, B.W. 2012. Ammonia emissions from cattle-feeding operations. Texas A&M Agrilife Extension. E-632. p.1-15. Interpretive Summary: This paper summarizes research concerning ammonia production, concentrations, and emissions at beef cattle feedyards, and summarizes methods that may potentially be used by beef cattle feedlots to reduce ammonia emissions. Ammonia (NH3) is a lighter-than-air, colorless gas, with a recognizable pungent smell. It is a source of the essential nutrient nitrogen (N) for plants, and animals, but is also classified as a hazardous substance by the EPA. Ammonia occurs naturally in trace amounts in the atmosphere. It is produced by the decomposition of animal, and plant matter including livestock manure. Concentrated animal feeding operations (CAFOs) such as feedyards are potential sources of ammonia. The production of ammonia is a complex of biological, and chemical processes, however the primary source at feedyards is urea excreted in urine. Ammonia losses can continue from immediately from excretion, and as manure is handled, stored, or applied to land as fertilizer. There are varieties of methods to measure atmospheric concentrations of ammonia, each with unique advantages, and disadvantages. Atmospheric ammonia concentrations at CAFOs vary greatly, but tend to be greater during daytime than at night. Ammonia concentrations at cattle feedyards rarely exceed 3 ppm. Methods for estimating ammonia emissions from feedyards also vary greatly. North American feedyard studies have observed ammonia emissions from 18 to 104 kg/head annually. Ammonia losses from runoff holding ponds have ranged from 3 to 70% of the N entering the pond, and ammonia losses from compost piles have ranged from 10 to 45% of the N entering the compost. Decreasing ammonia losses can improve air quality, and save valuable nitrogen (N) that can be used to fertilize crops. Ammonia abatement measures can be implemented at two different stages of livestock production. First stage measures are applied before the animal excretes the N. These include dietary strategies to reduce the amount of N excreted in livestock manure. In the second, or post-excretion, stage management strategies are implemented to reduce the amount of ammonia transferred to the environment from the manure. Presently, most of these methodologies are not economically viable. The most feasible methods currently available involve manipulating diets so that N excretion is decreased, but animal performance is improved or not adversely affected. Use of growth promoting regimens may not directly affect ammonia emissions but can decrease ammonia losses per unit of production. Covering stored manure, and incorporating manure when it is land-applied can significantly reduce ammonia losses.
Technical Abstract: Ammonia is a colorless gas with an pungent odor that occurs naturally in trace amounts in the atmosphere, where it is the dominant base. Ammonia is produced during the decomposition of livestock manure. There is concern about atmospheric ammonia because of its potential effects on air quality, water quality, and human/animal health. Because it is an essential plant nutrient, N lost to the atmosphere from manure is also a loss of fertilizer value. Concentrated animal feeding operations (CAFOs) import feed ingredients which contain nutrients such as N. Cattle retain a proportion of the N they consume, but 70 to 90% is excreted in feces, and urine. Ammonia is produced by breakdown of nitrogenous molecules in the urine, and feces. Urea in urine is rapidly (i.e within seconds) converted to ammonia, and is the major source of ammonia from manure. Differences in livestock digestive systems, diets fed, feed, and manure management systems, facility design, location, and weather are just a few of the factors that can affect ammonia emissions. Accurate measurement of the atmospheric concentration of ammonia in a large mass of dynamic, open air such as occurs over feedlots is difficult, and requires special instrumentation and/or significant labor inputs. There are varieties of methods available to measure atmospheric concentrations of ammonia, each with a unique set of advantages, and disadvantages. Atmospheric ammonia concentrations at CAFOs vary considerably, but tend to exhibit a 24-hour pattern, with daytime concentrations greater than nighttime concentrations. Ammonia concentrations at cattle feedyards rarely exceed 3 ppm. Ammonia emissions from CAFO are also difficult to measure because ammonia is quickly carried away by air currents. Methods used to estimate ammonia emissions from feedyards include mass balance, micrometeorology, flux chambers, wind tunnels, and dispersion models. The accuracy and applicability of these estimation methods varies greatly. Few statistical, empirical, and process-based models are currently available to estimate ammonia emissions from CAFOs. Reported emission factors for feedlots have ranged from 18 to 104 kg/head annually, and flux rates have ranged from 3.6 to 88 µg/m2/second. Most studies have also noted seasonal, and 24-hour patterns in ammonia flux rates. Reported losses from runoff holding ponds have ranged from 3 to 70% of the N entering the pond, and losses from compost windrows have ranged from 10 to 45% of the N entering the compost. Ammonia abatement measures can be implemented pre-excretion or post-excretoin phases. Pre-excretion techniques include nutrition-based strategies to reduce the amount of nitrogen (N) excreted in livestock manure. Post-excretion management strategies are implemented to reduce the amount of ammonia transferred to the environment from the manure. In some cases, it is possible to manipulate diets to reduce total N, and urinary N excretion while continuing to meet the nutritional requirements, and performance expectations of the animals. Several studies indicate that annual ammonia losses from beef cattle feedyards average approximately 50% of the N consumed by cattle: summer emission rates are about twice those in winter. Modifications of diet composition can effectively reduce ammonia emissions by 20 to 50% with only small effects on animal performance. Some of the dietary constituents that can be manipulated include concentrations of crude protein, degradable intake protein, fat, and fiber, and use of growth promoting feed additives, and implants. However, the large size of many CAFOs presents economic, and logistic challenges to modifying diets or feeding practices. Modifications to equipment, diets, or management practices may impose increased cost, labor, and time. Phase feeding involves adjusting nutrient intake over time to match the changing needs of the animal. If protein is progressively diminished through the feeding period, in balance with the animals' nutritional requirements, potentially less N is excreted, and less ammonia may be emitted. Manipulation of dietary fiber may also affect ammonia emissions from feedyards by altering microbial processes on the pen surface. Post-excretion ammonia abatement strategies can reduce the rate of N volatilization and ammonia emissions. Based on laboratory studies, a number of compounds can potentially be applied to feedlot pen surfaces to reduce ammonia emissions; among them are zeolites (a microporous, aluminosilicate mineral), fats, and urease inhibitors. Unfortunately none of these are economically viable at the present time. Frequent pen cleaning may help to capture N in the manure by decreasing losses to the atmosphere. Covering stored manure to reduce its exposure to elements such as sun, wind, and rain is effective at reducing ammonia emissions. Immediate incorporation or injection into the soil has been shown to significantly reduce ammonia losses when manure is applied to farmland.