Botanical characteristics, crop management and potential of Silphium perfoliatum L. as a renewable resource for biogas production: A review

• The long flowering time and soil coverage of silphium are ecologically valuable.
• The production of silphium in the first year is work and cost intensive.
• After the first year the care requirements and production costs are low.
• Silphium can compete with other energy crops in the dry matter yield.
• Silphium is an enriching, alternative energy crop for biogas production.

The growing awareness of the importance of biodiversity in agroecosystems to increase and ensure the supply of biomass has led to an interest from governments, farmers and biogas plant operators in alternative crops for biogas production. This article reviews the available research results on one such alternative crop, Silphium perfoliatum L., in terms of the requirements for biomass production and relevance as a biogas substrate. S. perfoliatum L. is a tall, perennial, yellow flowering plant with a high ecological value that is particularly suitable as an energy crop owing to its low maintenance requirements and high biomass and biogas yields. The crop is productive for around 15 years and is native to the temperate latitudes (of North America) and can be adapted to regions with similar climate conditions, like Europe. Currently, crop establishment is more successful when planted from seedlings as opposed to sowing seeds directly, owing to poor seed quality and lack of seed technology. Weed management measures are high in the year of establishment, but are not necessary in subsequent years. Harvesting at the end of the flowering season gives the best dry matter yields and provides material to make good silage. From the small amount of data currently available, the annual harvest yield (dry matter) is around 15 t ha−1 and the biomethane potential (35 days) is around 0.260 m3 kg−1 on an organic dry matter basis (around 20% lower than maize silage). There is still a great need for research on this crop, particularly in developing a seed technology, investigating its susceptibility to potential plant pathogens, finding a suitable herbicide for weed management in the establishment year, and investigating the effect of this biomass in full-scale biogas plants. Overall, this crop is a very promising alternative crop for biogas production.