Integrating Continuous Cover, Manure Management, and Anaerobic Digestion Strategies on a Pennsylvania Dairy Farm: A Life Cycle Assessment

Continuous vegetative cover practices and manure management strategies have been proposed as best management practices in dairy production but can be difficult to support financially. Anaerobic digestion (AD) has the potential to offer a financial incentive for farmers by utilizing manure and grassy biomass for biogas─a concept termed grass-to-gas (G2G). Life cycle assessment is applied to evaluate the environmental impacts (global warming potential (GWP), marine eutrophication potential (MEP), and acidification potential (AP)) of implementing these practices. Literature estimates informed changes in inputs and subsequent emissions from winter cropping, switchgrass cultivation, and manure and digestate management (i.e., subsurface injection and covered storage). The results show that G2G systems can reduce the GWP of milk by over 20% on average relative to the base case, with effects on the MEP and AP being mixed in part due to how continuous cover impacts feed production on the farm and imports from off-farm. Continuous vegetative cover reduced on-farm MEP with and without AD but led to increasing feed imports in most scenarios, decreasing the life cycle MEP benefits. Reducing herd size to avoid increasing feed imports led to milk losses lower than current dairy waste rates. Trade-offs were analyzed in the context of food–energy–waste relationships within integrated cropping, livestock, and AD systems.