Corn cobs could potentially represent $25,000-75,000 in additional revenue for an average-size farm (at $30-60/ton), reports the ethanol producer POET.

In just five years, the U.S. could produce 250 million gallons of cellulosic ethanol, some of which will come from corn cobs and corn stover. Before this happens, however, agriculture and ethanol producers will need to identify economically and environmentally sustainable methods for harvesting, storage and transporting these materials.

The Energy Independence and Security Act of 2007 provides for 36 billion gallons of renewable fuel in 2022. Only 42% of this target will come from corn starch-based biofuels. The remainder will come from energy crops, ag residues and municipal wastes.

John Deere, Archer Daniels Midland and Monsanto recently announced a commitment to explore technologies to turn crop residues into feed and bioenergy products.

And last year, Deere began working with POET to harvest cobs.

As Corn & Soybean Digest reported last December, Ty and Jay Stukenholtz, growers and agricultural engineers, Nebraska City, NE, have built a combine-mounted system to collect corn cobs. Along with BethPihlblad, an environmental biologist, they formed Ceres Agriculture Consultants, Waukee, IA, to market their Residue Recovery System.

This year, the company has a harvest contract with an ethanol producer that will fuel its plant's gasification system with stover. Ceres will collect average cob per acre yield and moisture content data. Variety and plant population have significant effects on cob yield, Pihlblad says.

THE STUKENHOLTZES' SYSTEM is bolted onto a standard combine and would be sold as an aftermarket attachment. In the future, combines with this collection system could also be leased, Pihlblad says.

Iowa State University (ISU) has tested a dual-stream, single-pass harvest system for corn stover for the three last harvests. Researchers have obtained 50% removal rates at up to 80% of the speed of conventional harvest, says Stuart Birrell, ISU professor of agricultural and biosystems engineering, who developed the system.

ISU is working with the National Soil Tilth Laboratory to evaluate 100% and 50% residue removal for effects on soil nutrient levels.

Birrell's harvest system attachments can be used on standard combines using a modified row-crop header and corn reel attached to the combine's front and a chopper and blower attached to the combine's back. ISU has used the attachments on a John Deere 9750 STS combine.

The University of Wisconsin-Madison (UW) has developed both single-pass and multiple-pass harvesting systems. A two-pass system would lay down a stover windrow to be collected later with a forage harvester or baler.

With current combine power levels, single-pass harvesters would need to go more slowly if they pick up more residue, says Kevin Shinners, UW professor of agricultural engineering.

Growers need to evaluate their own operations and economics as to which system to use. The key would be to eliminate non-value-added steps, Shinners says.

He is also evaluating pre-treatment systems. Ensiling stover in bags with certain additives could help break down cellulose, enabling growers to add value at the farm level. However, some ethanol plant process technologies may be unable to tolerate the acids produced by this initial fermentation. Additional moisture in the feedstock also would raise transportation costs.

PACKING HARVESTED STOVER so that it can be transported economically is a major issue. Currently, uncompacted stover density is about 3 lbs./cu. ft., when it should be 12-14 lbs./cu. ft. for economic transportation, Birrell says.

John Deere is evaluating existing and new solutions to harvest and collect biomass for power co-generation and cellulosic ethanol. The challenge is developing the infrastructure and technology to make feasible long-term aspirations for cellulosic ethanol, says Don Borgman, director, ag industry relations, John Deere.

Field compaction, soil health, transportation costs, handling efficiencies, storage and delivery timing all require more study and development, he says. “A lot of these questions must be answered before nailing down a specific machine configuration or harvest method.”

Sam Acker, director, harvesting marketing, Case IH North America, says that feedstocks will need to be clean and dry enough to store and preserve quality. If too wet, mold could form which may change the feedstock properties. Soil in the material could interfere with the feedstock-to-ethanol conversion process.

It may be important to develop a harvesting system that would collect just the upper half of the cornstalk with the grain because the bottom half of the stalk could be too wet to store for cellulosic ethanol production, Acker says.

“It may be difficult for stover to become a major ethanol feedstock based on moisture and densification challenges,” he says. Research suggests that harvesting cobs, however, could be economically viable. There appears to be a minimal detrimental effect from collecting cobs since they do not contribute significantly to soil fertility.

“Case IH is involved in the development of equipment to collect cellulosic material from corn and other crops that are financially viable throughout the feedstock chains,” Acker says.

Still, cob yield is often less than 1 ton/acre, Shinners says. While they are a good starting point, a variety of feedstocks will be needed to reach the RFS target.