Correspondence between Small- and Large-Scale Determinations of Ammonia Emissions from Dairy Barns

J.M. Powell
U.S. Dairy Forage Resh. Center,
Madison, WI 53706 USA

Dairy barns are known to be major emitters of ammonia. However, quantifying ammonia emissions from dairy barns is difficult due to their large volume, open ventilation, and other factors. Correspondence between ammonia emissions derived from small-scale and large-scale operational studies could facilitate and reduce the cost of ammonia emission research. We measured the impact of dietary factors and bedding on ammonia emissions from small-scale laboratory vessels and from dairy cows housed in tie-stall barn chambers. Results from the barn chambers were validated through mass N balances and comparison of data on feed intake, manure N excretion and ammonia emission with published values of these parameters. In the diet studies, average daily ammonia-N emission (g/cow/day) during spring (18.8) was more than twice those in early-fall (8.4) and about three times greater than during winter (6.7). There were no differences in emissions from cows fed corn silage or alfalfa-silage. During spring, emissions were greater from cows fed high protein than from cows fed low protein diets. In the bedding study, ammonia-N emissions (g/heifer/day) from animals bedded with manure solids (20.0), newspaper (18.9) and straw (18.9) were similar and significantly greater than emissions from bedding with pine shavings (15.2); emissions during summer (20.4) and fall (21.0) were similar but twice those recorded during winter (10.1). In both the diet and bedding studies across all seasons, ammonia-N emissions accounted for 1 to 7% of consumed feed N and 2 to 10% of excreted N. As observed in the small-scale laboratory studies, bedding types that physically separate feces and urine (e.g., sand, pine shavings) have lower ammonia emissions than bedding that fail to do so. The correspondence between results (ammonia emission per unit barn floor area) of the laboratory and barn studies suggest that the small-scale, laboratory methods will provide a useful tool for screening treatments before testing on a larger operational scale. Results from these large-scale chamber studies provided accurate information on seasonal differences in diet and bedding impacts on ammonia emissions from tie-stall barns. Confidence in study results were derived from (1) the relatively high chamber N balances (the ability to account for most all feed and bedding N inputs in ammonia N and animal milk and manure N outputs); (2) the favorable comparisons between study results and published values of ammonia emissions; and (3) the close agreement between study estimates and published values of excreted N and urine N.