Anaerobic digestion of manure - consequences for plant production

Summary

Organic farming systems are today dependent upon fossil energy. Another challenge are soil nutrient concentrations, which may be depleted with time even in animal husbandry systems (Løes & Øgaard 2001). Anaerobic digestion (AD) of animal manure may produce biogas to replace fossil fuels, and reduce methane (CH4) emissions during manure storage. Co-digestion of substrates rich in energy increases the economic viability of the biogas plant, and off-farm substrates such as fish silage or household waste may add nutrients to the farming system. AD may also ease manure handling, while reducing the amount of weed seeds and animal pathogens. A reduced proportion of easily degraded C in the AD-manure may however impact the soil fauna/microflora and humus levels. Mineralization of organic N during AD may increase nutrient availability and crop yields. Possibly, the increased levels of root and shoot residues may compensate for the organic C removed via AD.