Environmental assessment of United States dairy farms

Authors: Rotz, Clarence - Al; Stout, Robert; Leytem, April; Feyereisen, Gary; WALDRIP, HEIDI; THOMA, GREG - UNIVERSITY OF ARKANSAS; HOLLY, MICHAEL - UNIVERSITY OF WISCONSIN; Bjorneberg, David - Dave; BAKER, JOHN; Vadas, Peter; Kleinman, Peter

Submitted to: Journal of Cleaner Production
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/28/2021
Publication Date: 6/29/2021
Citation: Rotz, C.A., Stout, R.C., Leytem, A.B., Feyereisen, G.W., Waldrip, H., Thoma, G., Holly, M., Bjorneberg, D.L., Baker, J.M., Vadas, P.A., Kleinman, P.J. 2021. Environmental assessment of United States dairy farms. Journal of Cleaner Production. 315. Article 128153. https://doi.org/10.1016/j.jclepro.2021.128153.
DOI: https://doi.org/10.1016/j.jclepro.2021.128153

Interpretive Summary: Dairy systems of the U.S. are diverse, varying across the nation’s major regions and within individual states creating a challenge for accurate assessment of the environmental impacts of the dairy industry. A methodology was developed that uses simulation modeling and life cycle assessment of dairy farms to quantify important farm-gate emissions and resource consumptions at regional and national scales. The variability in environmental footprints of dairy farms was quantified as affected by climate, soil characteristics, animal diet, and farm management. Greenhouse gas emissions, fossil energy use and blue water use associated with dairy production were found to be relatively small compared to total estimates for the nation. Perhaps the greatest environmental concern is that of ammonia emission, where dairy farms may emit as much as 24% of the estimated emission for the whole country. Important mitigation needs include reducing ammonia emissions from manure sources, reducing water and energy use in feed production and reducing methane emissions from enteric and long-term manure storage sources. Results indicate that varied mitigation strategies tailored for individual farms are more effective than uniform application of specific strategies across all farms.

Technical Abstract: Dairy farms in the United States are diverse and although regional dairy production and farm strategy has been evaluated for environmental impact, a comprehensive national assessment is important to define national priorities for sustainable intensification. We estimated important environmental footprints of dairy production systems using process-level simulation and cradle-to-farm gate life cycle assessment. Dairy farms representing the sizes and management practices found in six regions were simulated with the Integrated Farm System Model (IFSM). Regional and national environmental footprints were determined as an average of all simulated farms weighted by the portion of milk contributed to the total. Nationally, dairy farms were assessed to emit 99,000 ± 8,480 Gg CO2e of greenhouse gas (GHG), equivalent to 1.5% of the estimated U.S. total GHG emission, with a commodity-based intensity of 1.01 ± 0.09 kg CO2e/kg of fat and protein corrected milk (FPCM) produced. Fossil energy consumption was 242,700 ± 38,400 TJ, 0.3% of the U.S. total, or 2.48 ± 0.39 MJ/kg FPCM. Blue (non-precipitation) water consumption was 11,600 ± 2,480 Tg, roughly 3.0% of the estimated U.S. total freshwater use, with an intensity of 119 ± 25 kg/kg FPCM. While these environmental footprints represent a small portion of the respective national inventories, the dairy industry’s contribution to reactive nitrogen (N) losses appears to be considerably greater. Losses of reactive N were estimated at 970 ± 133 Gg, with an intensity of 9.92 ± 1.36 g/kg FPCM. Although there are no national estimates of total reactive N emissions, dairy farms were found to contribute 19 – 24% of national inventories of ammonia (NH3) emissions. While strategies are available to reduce NH3 emissions, finding economical and sustainable solutions that do not result in pollution swapping remains a challenge for the dairy industry.