October 16, 2006
By Hal Bernton
MEAD, Neb. Duck beneath the green canopy of midsummer corn and you find the faded remains of last year’s harvest. The ground here is littered with a patchwork of withered husks, gnarled stalks and hunks of cob spread out over sandy soil.
Such leftovers may one day be a second farm crop, shipped off to a new generation of distilleries able to turn cellulose the tough fibers that form the inner walls of most plants into ethanol fuel for cars.
The biotechnology for a potential cellulose gold rush has been decades in development, with President Bush, in January’s State of the Union address, saying that federal research dollars would try to make the process “practical and competitive” within six years.
For an America now hooked on imported oil, cellulose offers an intriguing vision for the future by broadening an alternative fuel industry that now relies almost exclusively on corn kernels.
Cellulose is found in corn husks, wheat straw, trees, and fast-growing perennial crops such as switch grass, which is being grown on test plots in Nebraska, Washington and other states. A federal Energy Department study concluded that cellulose plant materials could help renewables supply 30 percent of the nation’s liquid fuel needs by 2030.
But tapping farm fields to produce both energy and food crops also creates new risks for agriculture and the environment.
Some cellulose materials such as the corn harvest leftovers already play an important role when returned to the soil. As they decay, they help fight erosion, improve the organic matter that is key to soil quality, and slow the release of carbon dioxide, a greenhouse gas that contributes to global warming.
Federal studies at the University of Nebraska’s research center in Mead indicate that on some lands all the corn residues should be left.
On others, only a portion should be removed, and researchers here are scrambling to develop new guidelines they hope farmers will respect.
“These crop residues are not being wasted. They are being used quite wisely,” said Wally Wilhelm, a federal plant physiologist who has spent much of the past quarter-century studying how crop residues return organic materials to the soil. “To wholeheartedly say that every wheat straw and cornstalk that is out there in November is now fair game that is not the way we need to do it.”
Researchers in Washington say that some wheat straw also should be returned to the soil.
“We have some high-rainfall zones that produce an abundance of wheat straw, and you could remove some without damaging soil fertility,” said Rick Koenig, a Washington State University researcher. “But in a lot of our drier areas, it’s best to return to it all to the soil.”
Nature points the way
The jungle rot that plagued GIs during World War II gave researchers early clues on how to turn cellulose into fuel.
Cellulose is formed by long chains of glucose molecules, which create very strong bonds that are hard to break down. But the cellulose in canvas tents, cotton uniforms and other World War II gear didn’t hold up under the assault of potent molds that the troops encountered in New Guinea and other tropical islands.
Army scientists sought to find ways to combat jungle rot, and noted that some of the most potent molds secreted an enzyme that rapidly broke down cellulose into glucose sugars. These sugars could be fermented into ethanol, opening the door in the post-war era for researchers to pursue cellulose-to-fuel technology.
But it has been difficult to reliably mass-produce the enzymes, then profitably convert cellulose into ethanol. A series of cellulose plants proposed over the decades were never built.
Given current technology, federal officials estimate production costs at about $2.25 a gallon more than double the production costs of corn ethanol from starch, according to Andy Aden, a cellulose specialist with the National Renewable Energy Laboratory in Golden, Colo.
Still, the federal government and corporations have stepped up research efforts to turn cellulose into fuel.
This summer, Xethanol, a publicly traded company, announced plans to build a 50-million-gallon-a-year cellulose ethanol plant in Georgia that would be fed by the forestry industry.
Iogen, a Canadian company that operates a small pilot project in Montreal, is considering construction of a wheat-straw plant in Idaho.
In the Midwest, major ethanol producers that process corn kernels are monitoring and, in some cases, investing in this research, hoping to eventually have the capacity to process cellulose pulled from the region’s vast fields of corn.
“There is an awful lot of good thinking about how do we find the silver bullet,” said Marty Lyons, a senior vice president for Archer Daniels Midland, the nation’s largest corn-ethanol producer and an investor in cellulose research.
If cellulose technology takes hold, ethanol yields from a corn field would receive a substantial boost. Fields that now produce enough corn kernels to yield about 400 gallons of ethanol per acre could produce as much as 280 additional gallons of ethanol per acre from the cobs, leaves and other cellulose material.
This might prompt some Midwest farmers to expand corn acreage, pushing into marginal lands more prone to erosion and leaching fertilizers and pesticides into waterways.
The government has sought to take such lands out of cultivation, paying farms to turn the acreage into conservation tracts typically planted in grasses that help hold the soil, provide cover for wildlife and protect the waterways. Currently, some 36 million acres of farmland are set aside in these reserves, with farmers receiving $1.76 billion annually not to grow crops on these tracts.
Rather than putting corn back into these lands, researchers have proposed planting some of them in switch grass, a native to the Midwest and one of four major prairie grass species that fed the vast herds of buffalo.
The hardy perennial can be grown in the same field for eight to 15 years in a row and provide cover for birds. The crop requires far less pesticides and fuel-intensive tractor work than corn. Its roots may extend some 10 feet deep, helping hold the soil in place. They also store large amounts of carbon, and thus help slow the release of carbon dioxide.
As an energy crop, the grass does have drawbacks. The huge bulk of the bales makes it difficult and expensive to transport over long distances to a distillery. Also, it is uncertain how well they would survive long periods of storage
But cellulose yields in test plots are impressive, with switch-grass tracts harvested once or twice a year estimated to produce from 200 to as much as 1,000 gallons of ethanol per acre.
In the Midwest, switch grass already is grown on some conservation-reserve lands.
Fields too dry
In Washington, it would likely have a smaller niche because most of the conservation-reserve lands are too dry in the summer to support switch grass, said Steve Fransen, a Washington State University forage agronomist at Prosser, Benton County.
The prime irrigated lands of the Yakima basin already claimed by orchards, vineyards, hops and other high-value crops could also grow switch grass if the payoff were high enough for farmers.
On test plots at the Prosser research station, Fransen and other researchers are experimenting with different varieties of switch grass to learn more about yields.
Fransen said a fresh summer planting of switch grass doesn’t look like much just a struggling patch of sod.
“It’s putting all of its energy into its roots and crown system,” Fransen said. “Then the next year, it just goes into this explosion.”
In some of the research plots, the grass has grown more than 6 feet tall. Meanwhile, the roots spread into a thick underground mat that reaches as much as 10 feet deep to soak up water and nutrients.
Switch grass could eventually be part of a broader mix of new ethanol crops that could include wheat straw, as well as fast-growing poplars, which already are grown in Eastern Washington by the timber industry. The emergence of such crops will depend on continued development of the cellulose-to-ethanol technology. And on whether oil prices stay high.
Federal officials are convinced that cellulose production costs can be cut to about $1.07 per gallon roughly half their current levels by 2012.
“It’s an aggressive track, but doable,” said Aden, the cellulose specialist at the National Renewable Energy Laboratory.