Practice Abstract 2 - Perennial grasses (grass-clover) as feedstock for biogas production and supply of organic digestate as fertilizer in Denmark

Perennial grasses (grass-clover) as feedstock for biogas production and supply of organic digestate as fertilizer in Denmark

As many organic farmers lack organic fertilizer to supply nitrogen to their crops for economic production levels, the current regulation allows fertilisation of organic fields with non-organic fertilizer e.g. manure from conventional pig and cattle farms. This contrasts to the original organic farming values regarded as a critical challenge for the future of organic farming. New ways of providing organic fertilizer must therefore be developed to further expand organic areas in Denmark, demanded by both consumers and political goals. A biogas plant has recently been deployed in Denmark on an organic vegetable and egg producing farm, with the purpose of producing fertilizer for farm fields and energy to the local municipality. The biogas output, ‘digestate’, is utilized as fertilizer - high in nitrogen content and other valuable macro and micro-nutrients depending on the feedstock used to feed the biogas plant. The current feedstock is primarily manure from chickens (250.000 egg producing hens), and grass-clover from 70 ha land. The farm is now self-sufficient with fertilizer (digestate), and capable of expanding the organic arable land even further. Besides digestate production, the biogas plant produces renewable energy in the form of methane gas, which - besides supply of heat and electricity to the local community – it could also be utilized for transportation purposes within the agro-sector. Separation of grass-clover in a protein and green stuff fraction is also interesting for farmers - ongoing research continues at Aarhus University, Denmark. Adding the gas rich green fibre fraction from grass-clover to the biogas plant, and using the protein-juice directly as animal fodder, will create multiple advantage of such biogas plants.