Manure-based biogas fermentation residues – Friend or foe of soil fertility?

• Anaerobic digestion improves nutrient content and availability compared to undigested manure.
• Anaerobic digestion does not impair soil organic C status.
• Anaerobic digestion decreases pathogen load of manures.
• Anaerobic digestion decreases overall greenhouse gas potential compared to classical manure treatment.
• Post-treatment like liquid–solid separation, drying or composting may exert additional positive effects.

Anaerobic digestion of organic residues has the potential to significantly contribute to a shift from fossil to renewable energy. The by-product, anaerobic slurry, does have properties that are different from the undigested material. There are concerns of soil organic matter depletion in soils, enhanced greenhouse gas and odour emissions, and pathogen spread upon production and use of biogas slurries as fertilizer. However, considering the pros and cons, anaerobic digestion of residues does have positive effects for the climate, the environment and for the farmer, compared to the use of undigested matter.