NEVADA, Iowa — One of the first and largest commercial-scale cellulosic biorefineries in the world will begin producing ethanol later this year.

The DuPont Cellulosic Ethanol facility is expected to generate 30 million gallons annually of biofuel produced from corn stover. Stover is the leaves and stalks left in the field as residue after harvesting.

To supply the corn stover for its plant, DuPont will contract from 450 to 600 local farmers to gather, store and deliver more than 375,000 dry tons of stover per year into the Nevada facility.

The stover will be collected from an approximate 35-mile radius around the new facility and harvested off about 200,000 acres.

The development of this facility has included key partnerships.

This is the first plant involved in working with the U.S. Department of Agriculture to promote sustainable harvesting of bio-based feedstocks for cellulosic-ethanol production.

Research in partnership with Iowa State University’s BioCentury Research Farm has been vital in the project in looking at production, harvest and transportation, storage and processing.

2010 Start

DuPont’s efforts began in 2010 with the harvest of corn stover from 2,000 acres and increased to 60,000 acres — about 550 fields — last fall, producing more than 170,000 large square bales.

Under the program, farmers enter into an agreement that allows DuPont to collect the stover in a timely manner after grain harvest.

“The timeline for farmers is critical,” said John Pieper, DuPont Industrial Biosciences stover feedstock workstream leader, at the company’s recent media event.

“Farmers are willing to give us access to their fields to harvest the stover after they’re done harvesting grain, but they don’t want us taking very long because they have other practices that they need to do in that field, whether it’s spreading manure, putting on fertilizer or tilling.”

Despite weather challenges last fall and the size of the acreage, the time demands were met.

Pieper said they were wrapping up moving the bales in February from the field edges to interim storage facilities.

A major piece of the research is to determine how much stover should remain on the fields and the amount to be harvested because of its benefits and limitations.

“However, stover is proportional in yield to grain. So the amount of stover we needed on top of the soil to protect it from erosion was sufficient over 40 years ago when we were producing about 100 to 120 bushels of grain and only about two and one-half ton of stover per acre,” Pieper said.

“Today we’re producing on these fields in central Iowa over 180 bushels per acre on average, and that means nearly five tons of stover per acre.

“That excess stover is problematic. It interferes with crop establishment and early growth for the next crop, immobilizes nitrogen and harbors crop pathogens.”

Stover Benefits

Benefits include protecting the soil from erosion, maintaining soil organic matter and cycling crop nutrients.

“When we put that carbon on top of the soil and till it back under, it does break down into carbon and replaces that soil organic carbon, which is important,” Pieper said.

“However, to manage those heavy stover yields, we have to do heavier and heavier tillage. In some parts of Iowa, we’re back to tillage equal to the moldboard plow.”

The research has included stover’s impact on early crop development. Two years of data indicate that five days after planting, there are about 6,000 more plants per acre already emerged in soil where stover was partially removed.

“Typically in this area, farmers plant between 30,000 and 36,000 plants per acre. So about 20 percent of the plants emerge faster rather than being delayed, and 30 days post-plant, we have the same population farmers expect to have emerged,” Pieper said.

DuPont’s system targets stover removal at two tons per acre, with the remaining 2.3 tons per acre from corn producing 180 bushels per acre yields left on the field. A shredding windrower spreads remaining stover in a uniform carpet that covers the field.

Better Yields

A partial stover harvest increased corn yield 93 percent of the time, with an average gain of 5.2 bushels per acre, according to field trials.

“When you translate that, even at $4 a bushel, that’s $20 revenue per acre for the farmer that goes right toward profit because he hasn’t had to do anything else to get those extra bushels,” Pieper said.

He estimates farmers will spend $15 per acre to replace nutrients taken off fields through stover harvest. They receive a $24 per acre direct payment from DuPont that may go up as much as 40 percent in the coming year.

Add to that the yield gain from stover management and farmers are receiving a net profit of $32 per acre when stover is harvested as a residue management tool.

“In addition to the value of the direct revenue, some can take advantage of things like eliminating the stalk chopper pass. We’re doing that for them. We go through with a shredder and leave some on field,” Pieper said.

“Forty percent of the farmers that participate in the program either have or indicated they intend to decrease their tillage and that’s a great thing.

“They know they no longer have to use aggressive tillage because they don’t have as much stover on the field to manage. If they eliminate a pass or use a lighter tillage tool, they’re saving money on their operation.”

“They also get to enter the field earlier in the spring. With fewer residues there to keep the soils cool in the spring, they can get in and plant earlier.”

He said field-specific soil health assessments are also conducted as part of the program.