Switchgrass, energy cane, napier grass and sweet sorghum are some options for Southeast growers as they strive to produce 10 billion gallons of cellulosic biofuels by 2022.
Federal law has mandated a replacement of 36 billion gallons of oil-based fuel by the year 2022. Recent USDA projections call for about 15 billion gallons of corn-based ethanol by 2022 and another billion gallons from soy-based biodiesel. The remainder of the 20 billion gallons is expected to come from cellulosic sources, including biomass crops.
Nearly 50 percent of the 10 billion gallons of cellulosic biofuel is expected to come from the Southeast.
Reductions in tobacco production and large fluctuations in peanut, cotton and grain crops over the past few years has created an interest among many farmers to find a stable alternative crop. To meet government mandated alternative fuel production levels there should be a ready made market for high yielding biomass crops.
The most oft-mentioned of these biomass crops is switchgrass, but there are other options. Speaking at the recent South Carolina Biomass Summit, University of Georgia Researcher Dewey Lee says the optimum biomass crop for the Southeast may be one that has yet to be closely examined.
“The one thing we do know about bioenergy is that it will have to be cheap, because that’s what Americans want. We have low cost energy now, because we subsidize it, and there’s little reason to believe we won’t continue to support low energy costs,” Lee says.
“In the Southeast we can produce sugar cane, sweet sorghum, sweet potatoes, even fruit for fuel. We can produce high volumes of agricultural crop residues like woody biomass, annual grasses like switchgrass, tropical corn, high biomass sorghum — we can produce all those crops, he adds.
“We can grow all those crops and more in the Southeast, the big question is can we produce these crops profitably. Having a market for a crop is one thing, having a market that will pay a farmer enough to make a profit on a crop is another thing,” the University of Georgia professor says.
“There are still technical hurdles we must get over to make any of these crops profitable. It currently costs $60-$80 a ton to produce any of these crops, but the industry says they can’t pay more than $15-20 per ton — that’s a technical problem we have to work out to make any of these possible biofuel crops profitable to grow, he adds.
Can it be sustained?
While ethanol production from corn is viable, the question is can we sustain the current 13-plus billion gallons and expand a couple billion more gallons by 2025? The profit margins for ethanol production are incredibly low and perhaps of equal concern the difference between production and use is too low to allow the industry much wiggle room.
It seems fairly clear that alternative biofuel from corn has about maxed out, unless there are new economic subsidies made available to ethanol production. With ethanol from corn maxed out, the next option is biomass crops. The question, Lee contends, is which one will be most efficient to produce, distribute and use.
Sweet sorghum production has been going on in limited acreage for more than 50 years. Unfortunately, we are still using most of the same varieties now that we used in production for livestock feed 50 years ago.
Even using older varieties, we can produce about the same amount of fuel per acre from sweet sorghum as we can from corn, according to Lee.
Sweet stem, or sweet sorghum has been grown for more than a century in the Southeastern United States in small plantings for making sweet syrup. It has several advantages over sugarcane, such as the ability to withstand dry conditions, requires less fertilizer, rapid growth rate, ease of planting, and lower cost of total fermentable sugars.
In the Southeast there is no doubt the vast amount of crop residue from cotton, peanuts and grain crops is huge. However, the value of crop residue as cover crops, for livestock feed and in building organic matter in the soil is too valuable to use them for alternative fuel.
If you add in the cost of harvesting crop residues and solving the technical problems associated with making fuel from them, it’s difficult to see how this is going to be a popular source of a base to make fuel, Lee contends.
Miscanthus can be established by rhizomes, plugs, or even seeded. In many parts of the Carolinas miscanthus grows wild along the roadsides. No one wants to plant a perennial crop for fuel that will become an invasive species.
Miscanthus is a tall perennial grass that has been evaluated in Europe during the past 5-10 years as a new bioenergy crop. It is sometimes confused with elephant grass (Pennisetum purpureum) and has been called both "elephant grass" and "E-grass".
Does well in cooler climates
A big advantage for miscanthus production in the U.S. is that it does well in cooler climates, which removes much of the competitive advantage for the Southeast. Like other bioenergy crops, the harvested stems of miscanthus may be used as fuel for production of heat and electric power, or for conversion to other useful products such as ethanol.
There is more documented research on switchgrass for biofuels than any other of the grass crops commonly mentioned for alternative energy. While some contend yields can reach 15-18 tons per acre, Lee says those type yields are extremely difficult to attain in the Southeast.
Switchgrass can be used in standard bales, pellets and other forms for use in hydroelectricity production. It does respond to nitrogen and does have some tolerance for drought. It doesn’t grow as well on lighter, sandier soils in the Southeast. Like miscanthus, switchgrass may be better suited for profitable growth in areas other than the Southeast.
Ben Legendre, LSU AgCenter sugarcane specialist, says research into what’s called energy cane — sugarcane that produces large amounts of plant matter with high sugar content — began in the early 1970s following the oil embargo. But after the embargo ended and gasoline prices retreated, interest waned.
Legendre said sugarcane varieties aimed at energy production are not appropriate for sugar production. He said researchers are looking for varieties that produce high yields of plant material — called biomass — and have capabilities for use in energy production.
In the Southeast, energy cane can regularly produce 20-25 tons per acre. It is planted by cane and has a larger stem than either switchgrass or miscanthus.
Carlos Riva, CEO of Verenium, whose company is actively involved in developing energy cane production in the Southeast, says, “Energy cane” is currently being grown at university test plots in the South, to see how well it produces (and how it fares in hurricanes).
Verenium has leased 20,000 acres to begin growing the crop on a large scale. Every acre of energy cane should yield 1,800-2,000 gallons annually (compared with 800 gallons for conventionally produced ethanol from sugar cane in countries like Brazil).
Sometimes called elephant grass or Uganda grass, Napier grass is well suited to production in the Southeast. Georgia researchers have been able to produce 20-25 tons per acre, using only 100 pounds of N per acre and no P or K.
It is native to the tropical grasslands of Africa. Napier grass is a tall perennial plant, growing to a height of 12-15 feet. It can’t tolerate cold weather and would have to be harvested prior to first frost, if used as a biomass crop in the Southeast.