Submitted to: International Conference on Greenhouse Gasses and Animal Agriculture
Publication Type: Proceedings
Publication Acceptance Date: March 4, 2013
Publication Date: June 23, 2013
Citation: Powell, J.M., Wattiaux, M.A., Rotz, C.A. 2013. Estimating ammonia and nitrous oxide emissions from dairy farms using milk urea nitrogen. International Conference on Greenhouse Gasses and Animal Agriculture. 7(2):276. Technical Abstract: Dairy farms emit ammonia (NH3) from barns, manure storage, and soils, which can be hazardous to human and ecosystem health. Emissions of NH3 also contribute indirectly to emissions of nitrous oxide (N2O), a potent greenhouse gas. Direct N2O emissions occur mostly from soil after application of fertilizer, manure, and other nitrogen (N) sources. Urinary urea N (UUN), the most labile N component of manure, is a principal N source of both NH3 and N2O emissions from dairy farms. The type and amount of crude protein (CP) fed to a dairy cow impacts UUN excretion and therefore NH3 and N2O emissions. Our recent analyses showed that the relationship between milk urea N (MUN) and UUN can be used to predict relative NH3 emissions from dairy barns. The objective of this study was to evaluate the efficacy of using MUN to estimate direct and indirect N2O emissions from dairy farms in Wisconsin (WI), USA. MUN records (37,889 cows; 197 herds in WI) over 2 years (2010-11) from the database of AgSource were partitioned into five MUN categories: =10, 11-12, 13-14, 15-16 and >16 mg/dL. UUN excretion (g/cow/day) was calculated from the equation UUN = MUN *16.23-34.2 (R2=0.79) derived from 9 lactation trials (37 dietary treatments) conducted in WI. UUN loss as NH3 and direct N2O loss from barns, manure storage, and soils were calculated for dairy farms having free stall barns, tie stall barns, and pasture-based farms using the Integrated Farm System Model, and indirect N2O-N emissions were estimated to be 1% of NH3-N emissions according to the Intergovernmental Panel on Climate Change. Approximately 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. Given that a MUN level of 10 mg/dL reflects adequate dietary CP for high milk production, these MUN frequency results suggest that about 77% of the surveyed cows consumed dietary CP in excess of requirement. Percentage UUN loss as NH3-N ranged from 40% (pasture-based farms) to 84% (tie-stall farms using stacked manure storage). Percentage UUN loss as direct N2O-N ranged from 1.4% when manure was hauled daily on either free stall or tie stall farms to 3.7% from pasture-based farms. Whole farm (barn, manure storage and land application) NH3-N losses (g/cow/day) were lowest (range of 61 for pasture-based to 86 for free stall) at MUN levels of 10 mg/dL and highest (107 for pasture-based to 172 for tie stall) at MUN levels of 16 mg/dL. Relationships between MUN and total (direct plus indirect) N2O loss (g/cow/day) were similar, but varied by production system: lowest (3.1 from tie stall to 5.0 from pasture-based) at MUN levels of 10 mg/dL and highest (5.5 from tie stall to 8.8 from pasture-based) at MUN levels of 16 mg/dL. Using the approximate proportion of WI dairy cows on free stall farms (50%), tie stall farms (40%) and pasture-based farms (10%), each decrease of 1 mg/dL in MUN in the range of 16 to 11 mg/dL would result in state-wide decreases in total N emission of approximately 12%, or 15 g of NH3-N plus N2O-N/cow/day. Each unit decrease in MUN can be achieved by reducing dietary CP concentrations by approximately 6 g/kg DMI. Substantial reductions in NH3 and N2O emissions from dairy farms can be obtained through manipulation of dietary CP, which can be monitored and adjusted using MUN.