Biogaserzeugung ohne Flächenkonkurrenz auf Basis von Zwischenfrüchten, Kleegras und Reststoffen

Summary

Cover or catch crops have beneficial effects for soil, water, erosion, etc. If harvested, they also provide feedstock for biogas without competition for arable land. The latter also applies to clover grass ley or other residues on organic farms without ruminants and for manure. With an explorative approach, combining field experiments and data collection of practical implementation, we investigated achievable yields and identified recommendations for practical use. Gross energy yields of cover crops varied between 700 and 2000 m³ methane (CH4) ha-1 in Austria. The energy return on energy invested (EROI) ranges from 4 to 7, if biogas is upgraded and com¬pressed for biofuel use. Therefore, about 1000 m³ CH4 ha-1 are remaining as net energy yield from 4.5 t of dry matter (DM). With an adequate harvesting process and a price of 85 € t-1 DM cost-covering can be reached with about 4.5 t DM ha-1. If positive side effects are taken into account, 2.5 t DM ha-1 may be sufficient. Even if harvested and organic matter relevant for humification is returned with digestate, beneficial effects of cover crops on soil, water and climate may be improved. 7 – 16 % of the gross biogas yield of cover crops are sufficient for the entire production of cover and main crop from cultivation to harvest including transport. Therefore biogas enables organic farming without fossil fuels. Tractors fuelled with CH4 to 70 – 80 % are already available.