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United States Department of Agriculture

Agricultural Research Service

Research Project: Forage Characteristics that Alter Feed Utilization, Manure Characteristics and Environmental Impacts of Dairy Production Title: Abatement of ammonia and nitrous oxide emissions from dairy farms using milk urea N (MUN)

Authors
item Powell, J Mark
item Rotz, Clarence
item Wattiaux, M -

Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 12, 2014
Publication Date: June 20, 2014
Citation: Powell, J.M., Rotz, C.A., Wattiaux, M.A. 2014. Abatement of ammonia and nitrous oxide emissions from dairy farms using milk urea N (MUN). Journal of Environmental Quality. DOI:10.2134/jeq2013.09.0375.

Interpretive Summary: Dairy systems produce emissions of ammonia, which can be hazardous to human and ecosystem health, and nitrous oxide, the most potent agricultural greenhouse gas. The urinary urea nitrogen (UUN) excreted by dairy cows is the principal nitrogen source that controls these emissions from dairy manure. Milk urea nitrogen (MUN) is a measure of feed nitrogen use efficiency that is used widely by dairy nutrition consultants and farmers to monitor and adjust dietary nitrogen intake by lactating dairy cows. Since MUN is quite easily measured and already being measured on dairy farms, we wanted to know if changes in MUN would correlate to changes in UUN and consequently in emissions of ammonia and nitrous oxide. We investigated (1) relationships between MUN, UUN excretion and emissions of ammonia and nitrous oxide from barns, manure storage and land components of commercial dairy farms in Wisconsin, and (2) how reductions in MUN may impact ammonia and nitrous oxide emissions on a state-wide basis. From 51% to 84% of UUN is emitted as ammonia, with lowest loss from pasture-based dairy farms (due to UUN conservation through direct deposition of manure in pasture) and highest loss associated with farms that manage tie stalls (due to non-incorporation of manure). Each decrease of MUN by 1 mg/dL (in the range of 16 to 10 mg/dL) would result in a 7% decrease in both ammonia and nitrous oxide emissions from dairy manure. On a whole-farm basis, the feeding of balanced rations to achieve MUN concentrations of 12 to 10 mg/dL would result in state-wide reductions in ammonia emissions of 35% to 42% and in nitrous oxide emissions by 18% to 21%. Large reductions in gaseous nitrogen emissions from dairy farms are achievable through reductions in dietary nitrogen intake, which can be monitored and adjusted using MUN. Given that MUN is already used widely by dairy nutrition consultants and farmers, an expanded environmental use of MUN would offer a practical approach toward the desired win-win outcomes of decreased feed costs and reduction in ammonia and nitrous oxide emissions from dairy farms.

Technical Abstract: Urinary urea N (UUN) excreted by dairy cows is the principal nitrogen (N) source that controls emissions of ammonia (which can be hazardous to human and ecosystem health) and nitrous oxide (the most potent agricultural greenhouse gas) from dairy manure. The objectives of this study were (1) to investigate relationships between MUN, UUN excretion and emissions of ammonia (NH3) and nitrous oxide (N2O) from barns, manure storage and land components of commercial dairy farms in Wisconsin, and (2) to evaluate how reductions in MUN may impact state-wide emissions of NH3 and N2O. MUN records of 37,889 cows in 197 herds in Wisconsin over 2 years (2010-11) revealed that 23, 24, 23, 16 and 14% of all cows had MUN concentrations (mg/dL) of =10, 11-12, 13-14, 15-16 and >16, respectively. Assuming that a MUN level of approximately 10 to 12 mg/dL reflects adequate dietary N for most Wisconsin cows it appeared that 53% to 77% of the tested cows were consuming dietary N in excess of requirement. This MUN distribution was used to calculate excretion of UUN, and the Integrated Farm System Model was used to calculate UUN loss as NH3 and N2O from the barns, manure storage and soils of five dairy system types: (1) FS-1: free stall barn, scraped manure, slurry storage, manure incorporation into soil within 2 days; (2) FS-2: free stall barn, flush removal, lagoon storage, 2 day incorporation; (3) TS-1: tie stall barn with daily haul, no manure incorporation; (4) TS-2: tie stall barn, stack storage, 2 day incorporation; and (5) Pasture: tie stall barn, daily haul, no incorporation, grazing for 6 months. From 51% to 84% of UUN is emitted as NH3, with lowest loss from pasture-based dairy farms (due to UUN conservation via direct deposition of urine in pasture) and highest loss associated with farms that manage tie stalls (due to non-incorporation of manure). Each decrease of MUN by 1 mg/dL (in the range of 16 to 10 mg/dL) would result in a 7% decrease in both NH3 and N2O emissions from dairy manure. On a whole-farm basis, the feeding of balanced rations to achieve MUN concentrations of 12 to 10 mg/dL would result in state-wide reductions in NH3 emissions of 35% to 42% and in N2O emissions by 18% to 21%. Given that MUN is already used widely by dairy nutrition consultants and farmers to monitor and adjust dietary N intake by lactating dairy cows, an expanded environmental use of MUN would offer a practical, straightforward approach towards multiple desired outcomes (decreased feed costs and reduced NH3 and N2O emissions) for dairy farmers and the dairy industry.

Last Modified: 10/20/2014
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