Miscanthus as biogas feedstock: influence of harvest time and stand age on the biochemical methane potential (BMP) of two different growing seasons

The use of perennial crops instead of maize as feedstock in biogas plants can be associated with multiple environmental and economic benefits. One promising species in this domain is the C₄-grass Miscanthus × giganteus. The use of its biomass can mitigate carbon dioxide emissions by substitution of fossil fuels, sequestration of carbon in soils and reduced fertilizing. We compared Miscanthus from two different old fields (established 1995 and 2008) at three different harvest dates over 2 years. While the harvest in spring, like usual for combustion purposes, led to relatively low methane yields per hectare, the harvest in autumn, when the biomass is still green, exceeded the average methane yields per hectare of maize. The comparison of different old Miscanthus fields showed that there is no significant difference in terms of biomass yield, specific BMP and BMP per hectare. Only the influence of repeated autumn harvest showed differences in the methane production per hectare between both stand ages. The methane yield of the younger stand did not change considerable, while in the older stand, the productivity decreased about 15% after 1 year.