A dual-stream, single-pass harvesting system to harvest corn and corn stover in two seperate streams is being developed by Stuart Birrell, an Iowa State associate professor of agricultural 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 -- the stalks, cobs and leaves -- when farmers bring in their grain. The stover could be the source of plant fiber that feeds the next generation of ethanol plants.
The researchers ran their latest version of a stover harvester through about 50 acres of corn near Ames this fall. The harvester dumps a crop of corn kernels into the combine's hopper and blows a crop of stalks, cobs and leaves into a trailing wagon.
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 also allows farmers to harvest grain and stover with one pass through a 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 said there is more development work to do:
* Increase harvest speed so that it can collect more stover. The machine can currently collect only 50% of the stover at normal grain harvesting speeds.
* Find a way to economically transport the harvested stover. Stover comes off the combine at a density of about 3 to 4 pounds per cubic foot; it needs to be about 10 to 12 pounds per cubic foot for efficient trucking.
* Find a way to store the stover. DOE has estimated a biorefinery would need at least 2,000 tons of biomass per day. A year's supply would cover 100 acres with 25 feet of biomass.
* Determine how much stover can be removed from fields and still return sufficent organic matter to soil for fertility and erosion control.
Birrell's stover harvesting research has been supported by a three-year, $180,000 grant from the U.S. Department of Agriculture and the U.S. Department of Energy and a two-year, $50,000 grant from Deere & Company of Moline, Ill.
Birrell said 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 into ethanol," he said. "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."
Adapted from Iowa State University press release.