Panicum virgatum, commonly known as switchgrass, is a perennial warm season bunchgrass native to North America, where it occurs naturally from 55°N latitude in Canada southwards into the United States and Mexico. Switchgrass is one of the dominant species of the central North American tallgrass prairie and can be found in remnant prairies, in native grass , and naturalized along roadsides. It is used primarily for soil conservation, forage production, game cover, as an ornamental grass, in phytoremediation projects, fiber, electricity, heat production, for biosequestration of atmospheric carbon dioxide, and more recently as a biomass crop for the production of ethanol and butanol.
Other common names for switchgrass include tall panic grass, Wobsqua grass, blackbent, tall prairiegrass, wild Agrostis, thatchgrass, and Virginia switchgrass.
Switchgrass is a diverse species, with striking differences between plants. This diversity, which presumably reflects evolution and adaptation to new environments as the species spread across the continent, provides a range of valuable traits for breeding programs. Switchgrass has two distinct forms, or "cytotypes": the lowland , which tend to produce more biomass, and the upland cultivars, which are generally of more northern origin, more cold-tolerant, and therefore usually preferred in northern areas. Upland switchgrass types are generally shorter, at ≤ tall, and less coarse than lowland types. Lowland cultivars may grow to ≥ in favorable environments. Both upland and lowland cultivars are deeply rooted, > in favorable soils, and have short . The upland types tend to have more vigorous rhizomes, so the lowland cultivars may appear to have a bunchgrass habit, while the upland types tend to be more sod-forming. Lowland cultivars appear more plastic in their morphology, produce larger plants if stands become thin or when planted in wide rows, and they seem to be more sensitive to moisture stress than upland cultivars.Establishing and Managing Switchgrass as an Energy Crop, Forage and Grazinglands, 2008.
In native prairies, switchgrass is historically found in association with several other important native tallgrass prairie plants, such as big bluestem, indiangrass, little bluestem, sideoats grama, eastern gamagrass, and various forbs (sunflowers, gayfeather, prairie clover, and prairie coneflower). These widely adapted tallgrass species once occupied millions of hectares.Switchgrass as a Bioenergy Crop, ATTRA - National Sustainable Agricultural Information Service, 2006.
Switchgrass’ suitability for cultivation in the Gran Chaco is being studied by Argentina's Instituto Nacional de Tecnología Agropecuaria (INTA).
After establishment, switchgrass management will depend on the goal of the seeding. Historically, most switchgrass seedings have been managed for the Conservation Reserve Program in the US. Disturbance such as periodic mowing, burning, or disking is required to optimize the stand's utility for encouraging biodiversity. Increased attention is being placed on switchgrass management as an energy crop. Generally, the crop requires modest application of nitrogen fertilizer, as it is not a heavy feeder. Typical nitrogen (N) content of Senescence material in the fall is 0.5% N. Fertilizer nitrogen applications of about 5 kg N/hectare applied for each tonne of biomass removed is a general guideline. More specific recommendations for fertilization are available regionally in North America. Herbicides are not often used on switchgrass after the seeding year, as the crop is generally quite competitive with weeds. Most bioenergy conversion processes for switchgrass, including those for cellulosic ethanol and pellet fuel production, can generally accept some alternative species in the biomass. Stands of switchgrass should be harvested no more than twice per year, and one cutting often provides as much biomass as two. Switchgrass can be harvested with the same farm equipment used for hay production, and it is well-suited to baler or bulk field harvesting. If its biology is properly taken into consideration, switchgrass can offer great potential as an energy crop.http://www.reap-canada.com/online_library/feedstock_biomass/Optimization%20of%20switchgrass%20management%20for%20commercial%20fuel%20pellet%20production%20(Samson%20et%20al.,%202007).pdf Samson, R., Bailey-Stamler, S., & Ho Lem, C. Optimization of Switchgrass Management for Commercial Fuel Pellet Production (Final report prepared by REAP-Canada for the Ontario Ministry of Food, Agriculture and Rural Affairs (OMAFRA) under the Alternative Renewable Fuels Fund). 2008
Considerable effort is being expended to develop switchgrass as a cellulosic ethanol crop in the USA. In George W. Bush's 2006 State of the Union Address, he proposed using switchgrass for ethanol; since then, over US$100 million has been invested into researching switchgrass as a potential biofuel source."Since that mention in the 2006, investment in switch grass has exploded, thanks in large part, experts say, to the President's speech. Venture capitalists have poured over $100 million into private companies that are exploring the technology necessary to convert switchgrass into fuel, and large publicly owned companies are also directing their research dollars into biofuels." Switchgrass has the potential to produce up to 380 liters of ethanol per tonne harvested; however, current technology for herbaceous biomass conversion to ethanol is about 340 liters per tonne. Iogen Corporation Iogen Corporation, 2009. By contrast, corn ethanol yields about 400 liters per tonne.Farrell, A.E. Ethanol Can Contribute to Energy and Environmental Goals. Science. Volume 311. 2006. 506-508.
The main advantage of switchgrass over corn as an ethanol feedstock is that switchgrass's cost of production is generally about 1/2 that of grain corn, and more biomass energy per hectare can be captured in the field. hus, switchgrass cellulosic ethanol should give a higher Crop yield of ethanol per hectare at lower cost. However, this will depend on whether the cost of constructing and operating cellulosic ethanol plants can be reduced considerably. The switchgrass ethanol industry energy balance is also considered to be substantially better than that of corn ethanol. During the bioconversion process, the lignin fraction of switchgrass can be burned to provide sufficient steam and electricity to operate the biorefinery. Studies have found that for every unit of energy input needed to create a biofuel from switchgrass, four units of energy are yielded. In contrast, corn ethanol yields about 1.28 units of energy per unit of energy input.Wang, M., Wu, M., & Huo, H. Life-cycle energy and greenhouse gas emission impacts of different corn ethanol plant types. Environmental Research Letters. Volume 2. 2007. 1-13. A 2008 study from the Great Plains indicated that for ethanol production from switchgrass, this figure is 6.4, or alternatively, that 540% more energy was contained in the ethanol produced than was used in growing the switchgrass and converting it to liquid fuel. However, there remain commercialization barriers to the development of cellulosic ethanol technology. Projections in the early 1990s for commercialization of cellulosic ethanol by the year 2000 have not been met. The commercialization of cellulosic ethanol is thus proving to be a significant challenge, despite considerable research efforts.
Thermal energy applications for switchgrass appear to be closer to near-term scale-up than cellulosic ethanol for industrial or small-scale applications. For example, switchgrass can be pellet mill that are subsequently burned in pellet stoves used to heat homes (which typically burn corn or ). Switchgrass has been widely tested as a substitute for coal in power generation. The most widely studied project to date has been the Chariton Valley Project in Iowa. The Show-Me-Energy Cooperative (SMEC) in Missouri Show Me Energy Cooperative is using switchgrass and other warm-season grasses, along with wood residues, as feedstocks for pellets used for the firing of a coal-fired power plant. In Eastern Canada, switchgrass is being used on a pilot scale as a feedstock for commercial heating applications. Combustion studies have been undertaken and it appears to be well-suited as a commercial boiler fuel. Research is also being undertaken to develop switchgrass as a pellet fuel because of lack of surplus wood residues in eastern Canada,Bailey Stamler, S., R. Samson and C. Ho Lem. Biomass resources options: Creating a BIOHEAT supply for the Canadian greenhouse industry. Final report to Natural Resources Canada, Ottawa. 2006. 38 pages as a slowdown in the forest products industry in 2009 is now resulting in wood pellet shortages throughout Eastern North America. Generally speaking, the direct firing of switchgrass for thermal applications can provide the highest net energy gain and energy output-to-input ratio of all switchgrass bioconversion processes. Research has found switchgrass, when pelletized and used as a solid biofuel, is a good candidate for displacing fossil fuels. Switchgrass pellets were identified to have a 14.6:1 energy output-to-input ratio, which is substantially better than that for liquid biofuel options from farmland. As a greenhouse gas mitigation strategy, switchgrass pellets were found to be an effective means to use farmland to mitigate greenhouse gases on the order of 7.6–13 tonnes of CO2 per hectare. In contrast, switchgrass cellulosic ethanol and corn ethanol were found to mitigate 5.2 and 1.5 tonnes of CO2 per hectare, respectively.
Historically, the major constraint to the development of grasses for thermal energy applications has been the difficulty associated with burning grasses in conventional boilers, as biomass quality problems can be of particular concern in combustion applications. These technical problems now appear to have been largely resolved through crop management practices such as fall mowing and spring harvesting that allow for leaching to occur, which leads to fewer aerosol-forming compounds (such as K and Cl) and N in the grass. This reduces clinker formation and corrosion, and enables switchgrass to be a clean combustion fuel source for use in smaller combustion appliances. Fall harvested grasses likely have more application for larger commercial and industrial boilers."Samson et al. 2007": http://www.reap-canada.com/online_library/feedstock_biomass/The%20Emerging%20Agro-Pellet%20Industry%20in%20Canada%20(Samson%20et%20al.,%202007).pdf R. Samson, S. Bailey and C. Ho Lem. The Emerging Agro-Pellet Industry in Canada. 2007"Samson et al., 2008": In regions where the potassium and chlorine contents of switchgrass cannot be successfully leached out for thermal applications, it may be that biogas applications for switchgrass will prove more promising. Switchgrass has demonstrated some promise in biogas research as an alternative feedstock to whole plant corn silage for biogas digesters."Frigon et al. 2008 http://www.gtmconference.ca/site/downloads/2008presentations/5B3%20-Frigon.pdf J.C. Frigon, P. Mehta, S.R. Guiot. The bioenergy potential from the anaerobic digestion of switchgrass and other energy crops. National Research Council Canada. Growing the Margins Conference: Energy, Bioproducts and Byproducts from farms and food sectors. April 2–5, 2008, London, Ontario Switchgrass is also used to heat small industrial and farm buildings in Germany and China through a process used to make a low quality natural gas substitute."plentiful_switchgrass"
Bai et al. (2010) conducted a study to analyze the environmental sustainability of using switchgrass plant material as a feedstock for ethanol production. Life cycle analysis was used to make this assessment. They compared efficiency of E10, E85, and ethanol with gasoline. They took into account air and water emissions associated with growing, managing, processing and storing the switchgrass crop. They also factored in the transportation of the stored switchgrass to the ethanol plant where they assumed the distance was 20 km. The reductions in global warming potential by using E10 and E85 were 5 and 65%, respectively. Their models also suggested that the “human toxicity potential” and “eco-toxicity potential” were substantially greater for the high ethanol fuels (i.e., E85 and ethanol) than for gasoline and E10.
In 2014, a genetically altered form of the bacterium Caldicellulosiruptor bescii was created which can cheaply and efficiently turn switchgrass into ethanol.
Soil erosion, both from wind and water, is of great concern in regions where switchgrass grows. Due to its height, switchgrass can form an effective wind erosion barrier. Its root system, also, is excellent for holding soil in place, which helps prevent erosion from flooding and runoff. Some highway departments (for example, KDOT) have used switchgrass in their seed mixes when re-establishing growth along roadways. It can also be used on strip mine sites, dikes, and pond dams. Conservation districts in many parts of the United States use it to control erosion in grass waterways because of its ability to anchor soils while providing habitat for wildlife.
Grazing switchgrass calls for watchful management practices to ensure survival of the stand. It is recommended that grazing begin when the plants are about 50 cm tall, that grazing be discontinued when the plants have been eaten down to about 25 cm, and that the pasture be rested for 30–45 days between grazing periods. Switchgrass becomes stemmy and unpalatable as it matures, but during the target grazing period, it is a favorable forage with a relative feed value (RFV) of 90–104. The grass's upright growth pattern places its growing point off the soil surface onto its stem, so leaving 25 cm of stubble is important for regrowth. When harvesting switchgrass for hay, the first cutting occurs at the late boot stage – around mid-June. This should allow for a second cutting in mid-August, leaving enough regrowth to survive the winter.
+Forage/Conservation varieties !Cultivar !Release Year !Ecotype !USDA Zones !Plant Introduction Number | ||||
Blackwell | 1944 | Upland | 5-7 | PI421520 |
Caddo | 1955 | Upland | 6-7 | PI 476297 |
Sunburst | 1998 | Upland | 3-5 | PI 598136 |
+Bioenergy varieties
!Cultivar
!Release
Year !Ecotype !USDA Zones !Plant Introduction number | ||||
BoMaster | 2008 | Lowland | 6-8 | PI 645256 |
Liberty | 2014 | Lowland | 4-6 | PI 669371 |
Independence | 2021 | Lowland | 5b-7b | PI 704577 |
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