Miscanthus versus switchgrass

Switchgrass has hogged the spotlight as a perennial grass suitable for cellulosic ethanol production in the United States. In Europe, however, miscanthus takes center stage. EPM looks at how the two compare.
By Susanne Retka Schill | October 03, 2007
When Stephen Long arrived at the University of Illinois, Urbana-Champaign (UIUC) in 1999 he was intrigued by all the attention on switchgrass. He had worked with miscanthus in England where widespread interest spawned over two decades of research in Europe. "When I came here the interest was in switchgrass," he says. "I was curious at how the two compared."

Miscanthus is used commercially for small-scale heat and power in Denmark and in the United Kingdom, where the first large-scale commercial project is being launched to cofire the largest coal-fired generator with 50 percent miscanthus. Other countries working with the biomass crop include Hungary, Germany, Austria, Italy and southern Sweden. While work on miscanthus began in the 1970s, "it's only really become commercialized in Britain in the past five years," Long says. Government incentives have been important in launching commercialization efforts. "You don't see any growers putting it in without some crop insurance or price guarantees from the end user," he says.

Miscanthus Growth
Long is leading the research effort started in 2001 at UIUC with the sterile cross Miscanthus x giganteous. The original material came from the Chicago Botanic Garden where it has been grown as an ornamental grass since 1977. The parent species have been in the United States for more than 100 years, he says. Like soybeans, the species originated in eastern China and Japan. Miscanthus has a larger growing region than soybeans, however, reaching to Papua, New Guinea, in the south and into Mongolia and the northern Japanese islands. That's important because it indicates there should be plenty of genetic material available to improve varieties for a wide range of growing conditions, Long says. Some mistakenly say the common name for Miscanthus x giganteous is elephant grass or bamboo, but Long says giant miscanthus is most closely related to sugarcane.

Giant miscanthus yields are impressive. Once established, the plots yield 14 to 17 tons per acre. The highest yield obtained from Illinois plots was 27 tons per acre. "The trick will be to find out how you can do that routinely," Long adds. Most recently, Frank Dohleman, a colleague of Longs at UIUC, published the results of his work where he identified the genes involved in the mechanisms that giant miscanthus uses to achieve its high rates of photosynthesis resulting in such vigorous growth.

Because the sterile plant produces no seeds, giant miscanthus is established by planting rhizomes. "It would be rather like planting a potato crop," Long says. Europeans have developed specialized machinery that can plant 30 acres a day. At Illinois they've used tree planters that can only cover four acres a day. Herbicides are used in the first year to reduce weed competition, but once established, giant miscanthus grows so quickly in the spring that it shades out any weeds. The stands also have long lives. "In Denmark they planted miscanthus 30 years ago," Long says. "They say they get 90 percent of the yield they got 25 years ago." He adds that the European stands have not seen pest or disease problems as yet.

The crop generally grows 11 feet tall, and will get as high as 14 feet. While one might expect such a tall crop to flatten and lodge in high winds or rains, it's not prone to lodging. "We've even had an ice storm where it was bent over, but it went back into position afterwards," he says.

Giant miscanthus is harvested in the fall after the first killing frost. The plant moves and stores its nutrients below ground for use the following spring. Europeans harvest it as late as March, although Long says he recommends a December harvest when the ground is frozen to prevent soil compaction from machinery. Furthermore, the cold air keeps the moisture content low. Standard hay cutting and baling equipment is used. The height creates the biggest challenge, Long says. "The tractor driver can't see where he's going," he says. "I have heard in large-scale plots in Europe they have to give the drivers a break because psychologically it's stressful when you can't see forward."

Long visualizes Illinois farmers planting giant miscanthus in a 10-year rotation, sowing grass in the poorest fields to take advantage of the crop's ability to build soil organic matter. After several years, the grass stand would be plowed and the ground would be returned to a corn-soybean rotation. A newer, improved giant miscanthus variety would then be planted into another field that required the soil-building crop.

"We've seen huge interest here from local farmers," Long adds. "They say if an [ethanol] plant came tomorrow and guaranteed the income they get from corn and soybeans, they'd grow miscanthus."

Switchgrass Comparison
Long's giant miscanthus research is tantalizing given its huge yields but work on the crop has only just begun. Researchers in Iowa, Alabama and Mississippi have planted test plots to see how the plant performs in those climates. If experience with switchgrass is any indication, there may be some regional differences.

Switchgrass in the South performs quite differently than in the Plains or the Midwest, explains David Bransby, professor of energy crops and bioenergy at Auburn University in Alabama. The variety Alamo, grown widely in the South, grows up to 9 feet tall, yields 7 to 8 tons per acre and tolerates poor soils. Bransby says they've concluded that in the South the best time to cut switchgrass is at the end of August or early September, which gives an optimal yield while allowing time for a 20- to 30-inch regrowth before entering dormancy for the winter. The re-growth suppresses winter weeds and provides a canopy to protect new shoots from late spring frosts as well as providing an ideal wildlife habitat.

In Nebraska, Ken Vogel has led the switchgrass research for the USDA Agricultural Research Service. The latest research, which is being reviewed before publication, provides the results of farm-scale trials conducted in cooperation with 10 farmers in Nebraska, North Dakota and South Dakota. The trials were quite realistic, Vogel says. Some farmers had grown switchgrass before, some followed the guidelines verbatim and others made changes in the recommended practices. The average yield over the four production years in the trial was 3.4 tons per acre per year. The two experienced farmers had the best results getting new stands established and maximizing yields. The farm trials helped identify the key management issues that will be of interest to new growers once it becomes a commercial crop. Profitability improves greatly if the grass can be quickly established to allow a first-year cutting and to reach maximum potential yield in the second year. "We can do it on the research plots," Vogel says, and the experienced farmers in the farm trials did so too, but the average in the farm trials was brought down by those fields that took three years to establish.

Researchers say switchgrass seeding will be a breeze for growers, compared with other biomass crops. Its smooth, shiny seeds make it easy to sow with existing equipment. The plants produce about 500 pounds of seed per acre and only 3 to 4 pounds per acre are needed to seed a new field. Other potential grass crops like prairie cord grass or big bluestem have rough or fluffy seeds that are harder to handle. Their lower seed production rates keep seed costs high. It costs $150 to $200 per acre to plant switchgrass because the crop requires substantial seedbed preparation, Bransby says. In addition, herbicides are used to suppress weed competition in new fields. Nitrogen requirements vary with the variety and the region. Vogel recommends 20 pounds of nitrogen for every ton of dry matter removed. If harvested after a killing frost, the fertilizer can be reduced by one-third to account for the nitrogen the plant stores in its roots for the next year's growth.

Switchgrass shows promise as a biomass crop for several reasons, David Parrish, crop and soil environmental scientist at Virginia Tech in Blacksburg, Va., wrote in his paper "Biology and Agronomy of Switchgrass for Biofuels." Switchgrass has been used on sites that are difficult to vegetate such as sand dunes and mining sites, and it facilitates the breakdown or removal of soil contaminates such as polychlorinated biphenyls, trinitolulene and herbicides. Switchgrass shows great tolerance to heat, drought and nitrogen stress. Parrish found yields varied greatly across the nation. In Tennesee and Oklahoma, the grass sustained yields of 20 metric tons per hectare (8.3 tons per acre). The highest single year yield topped 36.7 metric tons per hectare (17 tons per acre) in Oklahoma. He concludes that switchgrass varieties can be developed to consistently and sustainably produce 6 tons per acre in areas that receive 27 inches of annual rainfall.

The Bottom Line
For the cellulosic ethanol producer, the big question is how much the feedstock will cost. Bransby went directly to farmers and asked what they needed to be paid for a ton of switchgrass if it yielded 7 tons per acre and was delivered within 50 miles. "They tell me they'd be looking at $60 per ton," he says. That price could bring Alabama farmers over $100 per acre after paying for variable costs, which he says is better than most crops in the South.

"We think we can produce switchgrass in the Central Plains for $40 to $50 a ton at the farm gate," Vogel says. Adding transportation costs would net the grower a similar price to what the Alabama farmers could expect to receive. Using a projected ethanol yield of 80 gallons per ton, Vogel figures the feedstock cost would be about 50 cents per gallon, onto which transportation costs and biorefining costs would need to be added. Bransby says it will be critical to increase the ethanol yield per ton of biomass to make cellulosic ethanol economically viable. There is room for improvement, he says. The current estimate of 80 gallons of ethanol per ton of biomass is much lower than the theoretical maximum yield of 200 gallons per ton.

Vogel doesn't see switchgrass competing with corn and soybean crops because it would be grown on marginal land that is too steep, too sandy or too low in fertility to grow row crops. Also, he doubts it will be grown as an energy crop in the more arid region west of the hundredth meridian—roughly through the center of Nebraska where the Midwest meets the Great Plains. Further west, the lower yields would require transporting biomass further distances to supply refineries, making transportation costs uneconomical. However, on marginal cropland in the western Corn Belt, perennial biomass crops like switchgrass can potentially produce more ethanol per acre than corn. In the Central Plains trials, the average ethanol yields from switchgrass would amount to 450 gallons per acre or 79 gallons per ton.

The Illinois work on miscanthus does not include conversion technologies, but Iogen Corp. told Long that miscanthus, switchgrass and corn stover are all similar in sugar yields and a group from Michigan State University says it works well in their pretreatment process.

While the Illinois research has not advanced to farm-scale trials, early economic analysis shows some interesting comparisons. Madhu Khanna, in the Department of Agricultural and Consumer Economics at UIUC, figured out the annualized cost of production for switchgrass and miscanthus. The total operating cost using 2003 prices and including transportation to the refinery was $375 per hectare ($156 per acre) for switchgrass and $988.88 per hectare ($412 per acre) for miscanthus. The high cost for miscanthus reflects the high machinery costs for harvesting close to 20 tons per hectare (8 tons per acre) of miscanthus versus 5.78 tons per hectare (2.5 tons per acre) of switchgrass. When figuring the operating cost per ton, it was $65 per ton for switchgrass and $50 per ton for miscanthus. She also compared production costs with corn and soybeans, including the cost of switching corn and soybean acres into perennial grasses. She concluded that switchgrass production for biofuels will not be competitive with row crops in Illinois, but ethanol from miscanthus should be competitive with corn stover. Incentives for cellulosic ethanol from biomass crops would boost their competitiveness and might come from policies rewarding carbon sequestration or other soil benefits.

Fitting into the National Debate
Long suggests that the big yields from giant miscanthus are important because of the concerns about food versus fuel—the higher the ethanol yield from energy crops means that less land will need to be taken from food production. Using the target of replacing 20 percent of gasoline with biofuels within 10 years would require an estimated 35 billion gallons of ethanol. "With miscanthus you could do that with 8.2 million hectares (20 million acres)," Long says. If using mixed prairie grasses, as some have suggested as being more ecologically desirable, it would require 90 million hectares (222 million acres).

There is more to a biomass crop than sheer yield, Bransby says. His major concern with miscanthus is that it's not a native species, and may not gain the support of environmentalists. Switchgrass has under went numerous ecological studies showing that it supports a wide range of wildlife, while little is known about miscanthus and wildlife habitat. He adds that environmentalist support will be critical for the future of bioenergy. While many environmentalists are interested in mixed prairie grasses as a more ecologically and environmentally desirable energy crop, Bransby says that Minnesota work shows a yield of 1.7 tons per acre. "It's below the break even point," he says. "We need biomass fields between 4 and 5 tons per acre to make any money."

Switchgrass research dates back to the 1930s when researchers in the Central Plains were trying to improve pastureland. Both Vogel and Bransby started their work in energy crops in the early 1990s when the decision was made to focus on switchgrass as the model perennial grass. In 1985, the U.S. DOE began its herbaceous energy crop program coordinated by the Oak Ridge National Laboratory (ORNL) which evaluated between six and eight legume and grass species at several locations. Bransby remembers the questions that were raised when the ORNL team decided to focus on switchgrass. Looking back, he thinks it was the right call. Switchgrass has a wide genetic variation making it adaptable to different growing conditions. With the push for biofuels freeing up more resources for research, today increasingly more crops are being studied. Besides Long's work with giant miscanthus in Illinois, sugar cane is being studied along the Gulf, sorghum in Texas, and other perennial grasses such as reed canary grass and prairie cord grass in the Midwest.

Susanne Retka Schill is an Ethanol Producer Magazine staff writer. Reach her at [email protected] or (701) 746-8385.