Revised January 2023.
With corn and soybean acreage being planted to capacity for ethanol and biodiesel, other acreage unsuited for row crop production has been targeted for renewable biofuel production from perennial grasses. The most notable is switchgrass. However, another species called miscanthus sinensis, commonly referred to as miscanthus, is a biomass crop that some researchers believe can help diversify U.S. domestic energy production.
The five basic groups of sun-loving grasses can be classified by several widely grown examples. These include the Panicum-, Molinia-, Calamagrostis-, Pennisetum- and Miscanthus-types. Of these, the species in the Miscanthus genus are bulky, graceful and reed-like with well-developed seed heads on upright stems. Miscanthus sinensis is a large herbaceous perennial grass growing from 0.8 to 2.0 meters (rarely 4.0 meters) tall that forms dense clumps from underground rhizomes and has several zoological synonyms for varietal variants. It is known by the common name Chinese silver grass but also as maiden grass, zebra grass and porcupine grass. It flourishes in subtropical and tropical regions of Africa and southern Asia, and is said to be native to eastern Asia where it grows throughout most of China, Japan and Korea.
Miscanthus has been called “elephant grass” in the press, but true elephant grass is a distinctly different grass species. Miscanthus may be called elephant grass due to its vigorous growth and the large size it attains. Like elephant grass, miscanthus is also a common U.S. ornamental and has exhibited invasive characteristics.
Miscanthus is seen by some agriculturalists and bio-energy specialists as an ideal plant for producing fuel ethanol at a lower cost than corn, currently the most widespread source of the ethanol. Additionally, efficient biofuels are carbon-neutral sources of energy. Plants absorb atmospheric carbon dioxide during photosynthesis, which compensates for the carbon dioxide that is released when the biofuels are combusted. There have been reports in the popular press of miscanthus being commercially used in some European countries as a “clean, affordable, environmentally friendly energy cropping system;” however, this claim was difficult to substantiate for this article.
The Energy Biosciences Institute published an article that summarized current popular Miscanthus cultivars and energy research in the United States. It also notes the potential problems to its adoption as an energy crop. The authors state that the most promising cultivar put into production in the United States is Miscanthus x giganteus, which was originally collected in Japan in the 1930s and is a cross between Miscanthus sacchariflorus and Miscanthus sinensis. Research in Europe and the United States over the past 10 to 30 years on its agronomic potential has shown that the crop has many superior traits relative to other potential biofuel crops; however, limitations, disadvantages and information gaps exist concerning the cultivar. These include: lack of needed genetic diversity; its unknown long-term nutrient requirements (most research on nutrient cycling has been on stands less than 12 years old); unknown nutrient uptake and carbon sequestration at different depths in the soil profile; poor overwintering performance at more northern latitudes in Europe; and the difficulty of making new crosses due to non-overlapping flowering times of the parent species.
Another work, Miscanthus: A Potential Biofuel Source, a British Bio Fuel Hub article by Sabrine Daparine, notes some of the carbon sequestration and energy-equivalent data developed from research in the United Kingdom (U.K.). The British Bio Fuel Hub has reported that U.K. trials by the Perennial Bioenergy Crops Programme has produced 12 tons of fuel per hectare, and that one hectare of this perennial grass species can produce enough fuel to prevent 5 to 7 tons of carbon dioxide from being released into the atmosphere compared to fossil fuel. They summarize the following attributes of the crop: A coal substitute that produces only as much carbon dioxide as it consumes from the atmosphere as it grows; an efficient output fuel having an energy ratio of input to output of less than 0.2; this is relatively lower than the 0.8 energy ratio for ethanol and biodiesel from canola; and in addition to being a clean, efficient and renewable fuel source, Miscanthus also is very easy to grow with good yield on untilled soil, an effective land management measure that can lower carbon debt.
Currently, the main biofuel used in the United States is ethanol distilled from corn kernels. The Renewable Fuels Association (RFA) reports that as of 2022, there were 208 operating ethanol biorefineries in 25 states with a total capacity of 17.7 billion gallons. In his January 2005 State of the Union address, former President George Bush outlined his plan to reduce the nation's dependency on foreign oil by requiring the production of 35 billion gallons per year of renewable and alternative fuels by 2017.
Cellulosic Digestion/Cellulosic Conversion
Currently, there is considerable research into making corn-ethanol production far more efficient with the processes of cellulosic digestion and cellulosic conversion. This technology increases the production of “cellulosic ethanol,” which is distilled from the fermentation of sugars derived by also digesting the cellulose-containing plant tissues from the entire plant, not just the starch present in the seed grain. Some critics claim that this technology is still years off, although some existing older ethanol plants are being converted to test the new technology, a processing change that can increase ethanol-conversion efficiency by close to 30 percent.
Cellulosic conversion is particularly applicable to sugarcane, grasses and wood manufacturing co-products; residential yard waste; vegetable production co-products; and many other plant materials and waste streams including discarded paper that now goes into landfills. The technology uses microorganisms to digest the cellulose in the plant material for efficient conversion to sugar and then to alcohol or hydrogen. With the economic, social and political movement toward more U.S. energy self-sufficiency, economically viable biofuel crops could become important products from America’s agricultural regions.
Recently, several research groups formerly focused on the Human Genome Project have been isolating hundreds of promising bacterial enzymes from newly discovered microbes and investigating the potential for bacteria-aided conversion of biomass into ethanol. According to the Department of Energy's Joint Genome Institute, the microbes in one termite’s gut, for example, could produce more than a half-gallon of hydrogen from fermenting the sugars converted from the cellulose in a single sheet of paper. Most researchers feel that conversion technologies are in their infancy and that years of research may still lie ahead before efficient conversion technologies are routinely used. Also, for maximum efficiency and economical biofuel production, these complex bioprocessing and chemical engineering processes may need to be tailored to specific feedstocks at the expense of others.
Miscanthus vs. Switchgrass
There is no doubt that switchgrass, miscanthus and similar grasses provide wildlife cover, sequester carbon and have good soil-building characteristics. They have been experimentally used for biobased products that include building material wood-type and insulation material products. With respect to biofuel ethanol conversion, miscanthus is touted by some of its advocates as having twice the economic advantage over the more common switchgrass. Miscanthus produces about twice as much biomass per acre without irrigation as other grasses, requiring far fewer acres of land to obtain the same amount of material.
Miscanthus has the potential to be an excellent choice for energy production because it may be more economically viable than switchgrass, but switchgrass is already well established in wildlife management areas, erosion-prone situations, waterways, conservation set-asides and similar plantings. Farmers interested in producing miscanthus face the same challenges as those interested in producing switchgrass for biomaterial or biofuel markets; these include finding varieties suited to particular climatic zones, determining transportation economics and logistics to delivery points, and simply locating or developing processing ventures to take the material.
Miscanthus Production and Conversion
Miscanthus production and conversion has received attention by University of Illinois and Stanford University researchers. At the University of Illinois, an infertile hybrid that produces no pollen has been developed. This variety would have less genetically modified organism (GMO) or invasive species issues since it is incapable of sexual reproduction. This variety can grow over 12 feet tall and produce 10 tons of dry matter per acre. With respect to its energy value, miscanthus has been test burned as a pelletized fuel in heating units in a house on the University of Illinois campus. In this case, where the miscanthus plant material is directly pelletized in a pellet mill (no chemical or bioconversion) and is being burned, an applicable small-scale energy alternative, researchers calculated the cost of the energy at $5 to $6 per thousand BTUs.
With respect to the grass being a bio-energy feedstock for cellulosic conversion, economists believe there are significant chances for profitability. Profitability would be achieved through production efficiencies, close proximity collection and delivery points, and perhaps with additional financial assistance from carbon-sequestration credits. Currently, miscanthus agronomic and crop improvement research is in its infancy compared to that for corn and soybeans. Many researchers believe that if the technologies developed for these crops were applied to miscanthus the technological advances would not only help its development but synergistically assist cellulosic corn-ethanol technologies.
One concern regarding this crop is its potential as an invasive "weed" species. The National Biological Information Infrastructure (NBII) & IUCN/SSC Invasive Species Specialist Group (ISSG) updated its listing (2009) of this species. Miscanthus sinensis is a serious invasive species; however, Miscanthus x giganteus is sterile and not invasive.