Corn cobs could provide a future energy source, but farmers would have to receive a much higher price than previously thought to cover their costs and turn a profit, according to a Purdue University study.

Farmers would need to receive about $100 per dry ton from biofuels companies to persuade most to add a cob-collection operation during fall corn harvest, said agricultural economist Wallace Tyner and graduate student Matthew Erickson.

"That price is considerably higher than earlier estimates," Tyner said. "So while cobs could potentially become an important bioenergy feedstock, the high cost represents quite an impediment to development of the industry unless there are government subsidies."

Cellulosic biofuels can be made from cobs and other corn stover. A small percentage of corn farmers already collect cobs.

Tyner and Erickson found that more farmers might consider cob collection if the economic payoff was right. To determine economic feasibility, they examined a wide range of assumptions for cob collection, including the cost of cob-harvest equipment, the amount of time harvest is slowed by adding a cob-collection operation, the volume of cobs that could be collected per acre and other factors.

In addition to the $100 per ton price, the researchers discovered that farmers would be most likely to collect cobs if they made up at least 20 percent of the corn stover and rental charges for cob-collection wagons were half the standard $28,000 seasonal rate.

Cobs are collected in a motorized wagon hitched to the back of a combine. At the time corn grain is separated from plant stover by the combine, stover is blown into the wagon instead of onto the ground. The wagon then separates cobs from other stover, which is blown onto the field. Once the wagon is filled with cobs, it is emptied into a truck or a designated dumping area.

Tyner and Erickson surveyed farmers who supplied cobs to a Minnesota ethanol company in 2009. That information was used to create a cob-harvesting operation for Purdue's B-21 PC-LP Farm Plan Model, a computer program that determines the return on a specific farm operation from production and other entered data.

Anonymous data from 55 farms represented at Purdue's 2009 Top Farmer Crop Workshop was used as the base for the B-21 computer simulation. The farms harvested a combined 100,264 acres of corn without cob collection in 2008. In each case, the computer program provided the farms the choice between corn harvest with and without cob collection.