Environmental assessment of organic dairy farms in the US: Mideast, northeast, southeast, and mountain regions

Abstract

Greenhouse gas (GHG) emissions, ammonia (NH₃) emissions, eutrophication potential (EP), use of fossil energy, direct land, and blue water of organic dairy farms are evaluated in the Mideast, Northeast, Southeast, and Mountain regions of the US. Eighteen archetypical organic dairy farms are modeled with GHGs per kg fat and protein corrected milk (FPCM) ranging between 0.83 and 1.45 kg CO₂-eq with and 0.93 to 1.59 kg CO₂-eq without carbon sequestration. Enteric methane (CH₄) is the major contributor (42–58%) of farm GHGs, followed by CH₄ from manure (15–27%), energy use (8–18%), and material inputs (3–24%). Enteric CH₄ is affected by feed efficiency and milk production, manure CH₄ by the type of manure handled and stored, and GHGs from energy by the content of fossil-fuel sources in the electricity grid mix. Manure is the major source of NH₃ emissions ranging from 8.2 to 24.3 g/kg FPCM. Alternative GHG mitigation strategies show potential reductions of up to 23 and 51% for individual and combined strategies, respectively. While enteric CH₄ is the greatest GHG contributor, manure management has greater GHG mitigation potential. The choice of CH₄ predictive equations, N₂O emission factors, allocation, and functional units could increase GHGs up to 43% in the evaluated organic dairy farms.