Green Cheese: LCA of Energy Intensity and GHG Emissions of Integrated Dairy/Bio-fuels Systems in Wisconsin

Abstract

The objective of this study was to estimate the effects of dairy diets, manure-handling methods, and interactions with the bio-fuels industry on the net energy intensity, greenhouse gas (GHG) emissions, and land use for milk production in Wisconsin. Five dairy diets supplemented with varying amounts of co-products from corn ethanol and soybean biodiesel production were modeled in two manure management scenarios: with and without on-farm biogas generation. The diets were characterized by different inclusion of soybean meal (SBM) and dry distillers grains with solubles (DDGS), balanced with different types forages. A partial life cycle assessment (LCA) of milk production from cradle to farm gate was performed. Milk production was used as the primary output for this analysis, since the dairy industry will remain the primary agricultural enterprise in Wisconsin for the foreseeable future. The boundaries of the milk production system were expanded to include bio-fuels production. The production of bio-fuels (corn ethanol and biodiesel) was scaled to meet the dietary requirements of each selected dairy ration. The choice of dairy ration had a substantial effect on GHG emissions and net energy intensity per energy corrected milk (ECM) produced. Land use for the integrated dairy and bio-fuels production systems ranged from 1.68 m2/kg ECM to 2.01 m2/kg ECM. Accounting for bio-fuels credits but without biogas generation, net energy intensity ranged from 0.83 MJ/kg ECM to 1.34 MJ/kg ECM, and GHG emissions ranged from 0.69 kg CO2-eq/kg ECM to 0.80 kg CO2-eq/kg ECM, depending on the diet. The average effects of including anaerobic digesters for on-farm biogas generation were reductions in GHG emissions by 0.24 kg CO2-eq/kg ECM, and in net energy intensity by 2.84 MJ/kg ECM.