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.