If the ethanol industry is going to use the entire corn plant, there needs to be a revolution in how corn is harvested. The answer may be similar to the type of equipment you'd use on a lawnmower. The attachment to the combine would resemble a bagger - to gather and hold the stalks and leaves.
Iowa State University ag engineer Stuart Birrell and his team of researchers are developing and testing front and rear attachments that allow a conventional combine to harvest corn stover (stalks, cobs and leaves) as well as grain. Stover could be the source of plant fiber that feeds the next generation of ethanol plants.
"A significant amount of money and research has been devoted to the process of converting cellulose into ethanol," notes Birrell. "But very little money or effort has gone into answering how do you get a supply of stover from the field to the biorefinery. This will be critical to the success of the bioeconomy."
ISU tests system for collecting stover
The ISU researchers this fall field-tested the system they're developing to harvest corn stover and grain in one pass through the field.
In the tests, a John Deere 9750 STS combine slowly made its way through an ISU research field, all the while dumping crop of corn kernels into the combine's grain hopper and blowing a crop of stalks, cobs and leaves into a trailing wagon.
That dual-stream, single-pass harvesting system was developed by Birrell, an ISU associate professor of ag and biosystems engineering, and graduate students Mark Dilts and Ben Schlesser. They're working to design, build and test machinery that will harvest corn stover at the same time it brings in the grain.
The researchers ran their latest version of a stover harvester through about 50 acres of corn near Ames this fall. Birrell recently showed some video of the tests on his office computer and explained how the system works.
Developing a corn stover harvester
The researchers are developing stover attachments that can be used on standard combines. The result would be an additional cost to farmers of about $10,000 to $15,000 instead of the six figures it would take for a separate combine to harvest stover. The attachments would also allow farmers to harvest grain and stover with one pass through the field.
The system the researchers have come up with includes a modified row crop header and corn reel attached to the front of the combine and a chopper and blower attached to the back. The header and reel feed leaves and stalks into the combine so the biomass can be harvested before it touches the ground and is contaminated with soil. The chopper cuts stover into 2-inch pieces. And the blower throws the chopped stover into a wagon.
Although tests with the prototype machine have been successful, Birrell says there's more development work to do.
* Harvest capacity. The stover harvesting equipment is capable of speeds equal to a normal grain harvest when less than 50% of the stover is collected. When all of a field's stover is collected, harvest speeds are about half of a normal grain harvest. Birrell says that would be unacceptable to farmers.
So he's working to get the speed to at least 80% of a normal grain harvest—no matter how much stover is collected. That would allow farmers to decide how much stover they want to harvest without significantly affecting the time it takes to harvest their fields.
* Transportation. Birrell says researchers need to figure out how to pack the harvested stover so it can be economically transported. He says stover comes of the combine at a density of about 3 to 4 lbs. per cubic foot; it needs to be about 10 to 12 lbs. per cubic foot for efficient trucking.
* Storage. Researchers need to figure out how huge quantities of biomass can be stored. Birrell says the U.S. Department of Energy has estimated a biorefinery would need at least 2,000 tons of biomass per day. A year's supply would cover 100 acres and the biomass would be stacked 25 ft. deep.
* Fertility. Agronomists need to determine how much stover can be removed from fields while still returning sufficient organic matter to the soil and protecting the soil from winter erosion.
Birrell's stover harvesting research is supported by a 3-year, $180,000 grant from USDA and the U.S. Department of Energy, and a 2-year $50,000 grant from Deere & Co. headquartered at Moline. Birrell says development of a stover harvesting system has been constrained by a lack of research funding.
"Significant resources have been dedicated to the process of converting cellulose to ethanol," he says. "But very little has gone into answering –How do you get a supply of stover from the field to the biorefinery? This will be critical to the success of the bioeconomy."