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New Energy Economics: Corn Stover Harvest Challenges

Cole Gustafson, NDSU Biofuels Economist Cole Gustafson, NDSU Biofuels Economist
The price of these dedicated corn stover and cob harvesters is significant.

By Cole Gustafson, Biofuels Economist

NDSU Extension Service

On Nov. 3, I participated in the Poet Corp.’s corn stover harvest demonstration day in Emmetsburg, Iowa. Despite 35-degree temperatures and drizzle, it was fun to see a dozen different machines and technologies for collecting corn stover biomass for Poet’s cellulosic ethanol plant next door. All of the machines operated flawlessly, but economic implications varied considerably.

Initially, Poet had emphasized corn cobs because the cobs were energy dense compared with the rest of the corn plant material and did not contain many nutrients. Several machines operating on Nov. 3 strived to collect just corn cobs and remove other plant material, such as husks and corn stalks. These machines produced piles of corn cobs that were very clean.

Poet later found that its cellulosic ethanol conversion process could accommodate more plant material, in addition to just the cobs. In fact, it coined a new term: material other than cob (MOC). In proposed contracts to producers, Poet feels it can take up to 25 percent MOC in addition to the corn cobs.

In response, several equipment manufacturers have developed machines that collect larger amounts of MOC corn stover. Many were traditional large square balers that had the hay pickup mechanisms removed and replaced with belts to pick up all of the material exiting the combine. Most were driven by the combine’s original hydraulic system, but one did have an additional hydraulic pump installed.

After these large, square balers compacted everything exiting the combine, the bales looked like a bale of corn stalks. Very few cobs could be seen. However, on a dry-matter basis, Poet felt that these bales, even with only a few visible cobs, would qualify as 25 percent MOC because the husk was so light compared with the cobs.

This raises an interesting economic question regarding transportation costs. Including 25 percent MOC significantly increases bale size and bulk but apparently doesn’t add much to the total dry-weight matter or value. Thus, producers likely will incur higher transportation costs because they won’t be able to load as efficiently. However, it is a more simplistic machinery design and operation process.

The price of these new dedicated corn stover and cob harvesters is significant. Manufacturers suggest that retail prices likely will exceed $130,000 once commercial production begins.

Poet supplied draft purchase contracts to interested farmers. In summary, it proposes to pay $55 per ton and wants the material to be as dry as possible. Given the investment cost of the new dedicated stover/cob machines, sizeable acreage will be required to justify the cost.

Initially, producers will be able to augment their returns if they sign up with the Farm Service Agency’s Biomass Crop Assistance Program. Participants will receive matching revenue up to $45 per ton.

However, the return on investment is going to face several challenges. There are far fewer corn cobs per acre than many producers expected. During the demonstration day, Poet had five combines each taking eight rows that were approximately a one-quarter-mile long. The size of the piles at the end of the day wasn’t as large as I expected. The manufacturers on hand that day indicated they were obtaining from 3/4 ton to 1 1/4 tons per acre.

Second, the corn cobs were quite wet because they typically dry down after the grain. Corn grain being harvested that day was under 20 percent moisture, but the cobs were estimated to be between 35 percent and 40 percent moisture. Poet expects to store the cobs outside and lose about 18 inches of material on top.

A pleasant surprise was that none of the machines really took away valuable field time. In fact, farmers should think of it as a bonus activity. It is something to do if time allows. Most units entered the rows and started harvesting grain as usual. After the operators became settled with grain harvesting several yards down the row, the stover collection systems were turned on. Many of the systems had quick disconnects or diversions so that producers could focus on the grain harvest and not collect cobs if time did not allow or the fields were too muddy.

The machine technology appears to be here; now all we need are cellulosic ethanol plants to buy the product.

NDSU Agriculture Communication

Source:Cole Gustafson, (701) 231-7096,
Editor:Rich Mattern, (701) 231-6136,
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