A new study led by researchers at Penn State finds that anaerobic digestion, when paired with continuous crop cover, could reduce the carbon footprint of dairy production by more than 20%. The findings add to growing evidence that anaerobic digestion can play a meaningful role in agricultural climate strategies, while also underscoring the importance of system-level planning.

Published in Environmental Science and Technology, the study evaluated a modeled large-scale dairy farm in Pennsylvania using a “Grass2Gas” approach. The system combines year-round vegetative cover with anaerobic digestion of manure and additional grassy biomass to produce biogas for energy. Compared with conventional manure management, the modeled system delivered substantial greenhouse gas reductions driven largely by methane capture and renewable energy generation.

However, researchers caution that the benefits are not universal or automatic. While continuous crop cover reduced nutrient runoff locally, the need to grow additional biomass for digestion increased reliance on off-farm feed imports in many scenarios. From a full lifecycle perspective, those imports offset some water quality gains and introduced new environmental trade-offs.

“Our research highlights the complexities of integrating anaerobic digestion into farm systems, including the impact on soil biogeochemistry and nutrient balances,” said Christine Costello, assistant professor of agricultural and biological engineering at Penn State and senior author of the study.

The study also examined digestate management, noting that anaerobic digestion alters how nitrogen is stored and released. Digestate behaves differently than raw manure in soil and air, affecting emissions of ammonia, nitrous oxide, and nitrate. These shifts make nutrient management practices critical to realizing climate benefits without creating unintended impacts.

Researchers found that reducing herd size to better match on-farm feed production resulted in modest milk losses comparable to typical supply chain waste, suggesting that emissions reductions do not necessarily require major production sacrifices.

Anaerobic digestion should be evaluated not as a standalone technology, but as part of an integrated farm, energy, and nutrient management system.