Miscanthus as biogas substrate – cutting tolerance and potential for anaerobic digestion

Abstract

AbstractIn the anaerobic digestion and biogas industry in Germany, the step of energy crop production accounts for a high proportion of the greenhouse gas emissions and environmental impacts. Replacing annual energy crops, for example maize, by perennial biomass crops such as miscanthus offers the potential to increase the sustainability of biogas crop production. However, the cutting tolerance of miscanthus and the mechanisms influencing it need to be investigated to assess its potential as a biogas crop. For this purpose, a field trial with different harvest regimes was conducted to identify the potential methane yield and cutting tolerance of Miscanthus x giganteus. Several fertilization regimes were tested under nitrogen‐limited conditions in a pot trial to investigate the mechanisms behind the cutting tolerance. The refilling of carbohydrate (starch) stores in the rhizome was identified as a very important factor influencing the cutting tolerance of miscanthus, whereas the nutrient relocation appeared to be of less importance. The field trial revealed that Miscanthus x giganteus offers a very high methane yield potential of approx. 6000 m3 ha−1 when harvested in October, which is within the range of the methane hectare yield of energy maize. The substrate‐specific methane yield of Miscanthus x giganteus biomass decreased with later harvest dates and reached 247 ml (g oDM)−1 in October. This harvest date delivered very high, stable yields of on average 26 t DM ha−1 over two years and enabled a good cutting tolerance. Green harvest in October was identified to be suitable for Miscanthus x giganteus and is recommended for biogas utilization. In conclusion, the perennial biomass crop Miscanthus x giganteus is a very promising biogas crop and offers the potential to increase the sustainability of the anaerobic digestion sector in Germany by replacing a substantial area of biogas maize cultivation.