Digestate from Biogas and Agricultural Soils: Key Factors Influencing Soil Quality and Organic Matter

Presented during the ClimateSmartAdvisors 2025 Thematic Knowledge Exchange webinar Digestate from biogas – what impact on agricultural soils, this practice addresses the question of how digestate spreading affects soil quality. Anaerobic digestion is often criticised for possible negative effects on soil, but digestate spreading should be assessed as part of the broader issue of soil organic matter, soil life, and the full anaerobic digestion cycle on farms.

The effect of digestate on soil depends on several interlinked factors. One key factor is the nature of the inputs used in anaerobic digestion, such as slurry, manure, crops, agricultural and industrial waste, unpackaged products, dry matter content, and degradability rate. The more degradable the inputs are, the more biogas they produce, but the less organic matter they return to the soil. Some industrial inputs, especially unpackaged products, may also contain undesirable materials such as plastics, metal, or glass. The origin of inputs also matters, since importing organic matter from outside the farm can help return carbon to soils. The type of digestate spread is equally important: raw, solid, and liquid fractions do not have the same effect, as most organic matter is found in the solid phase. In addition, storage conditions, especially whether storage is covered, influence nitrogen losses.

The effect of digestate on soil depends on several interlinked factors. One key factor is the nature of the inputs used in anaerobic digestion, such as slurry, manure, crops, agricultural and industrial waste, unpackaged products, dry matter content, and degradability rate. The more degradable the inputs are, the more biogas they produce, but the less organic matter they return to the soil. Some industrial inputs, especially unpackaged products, may also contain undesirable materials such as plastics, metal, or glass. The origin of inputs also matters, since importing organic matter from outside the farm can help return carbon to soils. The type of digestate spread is equally important: raw, solid, and liquid fractions do not have the same effect, as most organic matter is found in the solid phase. In addition, storage conditions, especially whether storage is covered, influence nitrogen losses.