An 80-acre field of stover stacked six bales high will be required to feed DuPont’s 28-million-gallon cellulosic ethanol plant.
Commercial-scale plants being built in Midwest
Dairy producers buying feed and competing for land have little good to say about ethanol made from corn. There may be a glimmer of relief on the horizon as two commercial-scale cellulosic ethanol plants rise from the Iowa prairie and become operational next year.
These plants alone won’t replace the 5 million bushels of corn now flowing into ethanol plants. But they could produce 16 billion gallons of ethanol by the end of the decade.
"Once we get the first plants going, we’ll be able to ramp up quickly," says John Pieper, director of cellulosic ethanol development for DuPont Industrial Biosciences. "We can make a lot of ethanol out of corn stover, and anything we do will take the pressure off of grain."
Poet Ethanol Products and its Dutch partner, Royal DSM, broke ground on a 25-million-gallon cellulosic plant at Emmetsburg, Iowa, earlier this year. DuPont, parent of Pioneer Hi-Bred, hopes to build a 28-million-gallon plant near Nevada, Iowa, later this year.
The cellulosic conversion process has proven itself in smaller pilot plants. DuPont produced 250,000 gal. of cellulosic ethanol from corn stover last year in its Vonore, Tenn., demonstration plant.
One of the biggest challenges for the new plants will be stockpiling enough corn stover. Each of these "big steel cows," as Pieper describes them, will eat their way through some 300,000 tons of stover each year. That’s 80 acres of 1,000-lb. cornstalk bales stacked six high.
Pieper estimates the Nevada plant will draw in stover from a 30-mile radius. That’s because DuPont is limiting the fields from which it takes stover.
Andy Heggenstaller, an agronomy research manager for DuPont, says it’s critical that enough stover be left on fields to maintain soil fertility and organic matter, and to prevent water and wind erosion. To meet those parameters, DuPont won’t harvest stover from fields unless they have an average corn yield of 180 bu. per acre and an average slope of 4% or less.
Even then, DuPont will harvest only 75% of qualified acres from land planted to continuous corn, or take stover off those fields three out of four years. If the land is in a corn-soybean rotation, it will harvest only 40% of qualified acres each year.
Currently, DuPont is taking 2 tons per acre, paying a minimal price. But it hopes that stalk removal will have enough additional benefits to entice corn growers to participate.
As corn yields increase, so do stover yields. A 210 bu. per acre crop yields 5 tons per acre, and a 295 bu. per acre crop yields 7 tons per acre.
"More than 4 tons per acre becomes a challenge to manage, and right now tillage is the only means to deal with it," Heggenstaller says.
Removing some of the stover means the soil warms up sooner in spring, seed placement is more uniform, less nitrogen is immobilized, fewer insect pests and corn pathogens survive winter, and the amount of tillage can be reduced.
- June/July 2012