Submitted to: International Journal of Molecular Sciences
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 12, 2008
Publication Date: May 16, 2008
Citation: Sanderson, M.A., Adler, P.R. 2008. Perennial forages as second generation bioenergy crops. International Journal of Molecular Sciences. 9:768-788.
Interpretive Summary: Second generation bioenergy crops, based on perennial forage crop species, are considered to be the future of the bioenergy industry and are the focus of intense research. In this paper we discuss some of the forage crops proposed for bioenergy use along with their environmental impacts, energy balance, research needs, and explore the implications of their widespread use. In the USA, research on perennial bioenergy crops during the last two decades has focused on switchgrass, a native warm-season perennial grass. Other forage crops with potential as biomass energy feedstocks include alfalfa, reed canarygrass, bermudagrass, and several tall-growing subtropical grasses. In addition to using new plantings of perennial bioenergy crops, other grassland-based resources such as set-aside lands along with marginal or abandoned lands could supply bioenergy feedstock. Combining annual bioenergy crops such as corn and sorghum into rotations with perennial bioenergy crops may benefit bioenergy cropping systems. Relying on a diversity of crops and cropping systems in farm landscapes and larger scales would endow future bioenergy production systems with greater stability, resistance, and resilience to climatic and other environmental shocks. Progressing to the second generation of biofuels will require transitions in the forage-livestock industry and in agriculture as a whole to accommodate both fuel and food production. Perennial forages used as biomass feedstock crops are a key component of this transitional process.
The lignocellulose in forage crops represents a second generation of biomass feedstock for conversion into energy-related end products. Some of the most extensively studied species for cellulosic feedstock production include forages such as switchgrass (Panicum virgatum L.), reed canarygrass (Phalaris arundinacea L.), and alfalfa (Medicago sativa L.). An advantage of using forages as bioenergy crops is that farmers are familiar with their agronomic management and already have the machinery, technology, and infrastructure needed to establish, manage, harvest, store, and transport them. Forage crops offer additional flexibility in management because they can be used for biomass or forage and the land can be returned to other uses or put into crop rotation. The billion-ton biomass vision for 2030 developed by the US-DOE and USDA envisions about a third of biomass would come from dedicated perennial energy crops (i.e., forages), requiring about 22.3 million ha of cropland, idle cropland, and cropland pasture. Converting these lands to large scale cellulosic energy farming could push the traditional forage-livestock industry to ever more marginal lands. Furthermore, encouraging bioenergy production from marginal lands could directly compete with forage-livestock production.