Can fields handle less stover?
MADRID – Iowa’s two planned cellulosic ethanol plants are set to provide an extra revenue stream for corn growers, but Iowa State University agronomists said farmers should look first before taking the leap to sell stover from their fields.
DuPont, which is building a cellulosic plant in Nevada, called a gathering of 60 farmers on Feb. 28 in Madrid to discuss how it will be seeking contracts to harvest stover from fields in a 60-mile radius from the plant.
But before the company offered its pitch, ISU ag engineers and agronomists, and farm managers took the floor to encourage producers to carefully assess if their fields can sustain the loss of the stover, which could throw their soil profiles out of balance in terms of organic matter that creates healthy tilth, prevents or slows erosion, sequesters carbon and adds moisture storage capabilities.
Stover, said David Ertl, representing the Iowa Corn Promotion Board, “is more valuable than trash.” Trash is farm-speak for leaving residue on the field
“But soil types dictate the amount of (stover) that can be removed.” It also determines how much nutrients will have to be added to replace the loss of corn stalks, leaves and cobs.”
“With the right amount of tillage,” Ertl said it can be managed. This is a young industry and we’re still learning how to remove the stover.”
Balance is needed
Mahdi Al-Kaisi, an ISU agronomist, hammered home to producers the need to closely study if any of their fields can be safely considered candidates for stover removal.
He said they need to look for the balance between production and soil quality, before selling their stover which will deprive fields of a certain amount of organic matter, in turn affecting moisture storage and chemical inputs required the next growing season and runs higher risks for water and wind erosion.
He presented charts on research the impact of stover removal on two ISU research farms with different types of soil profiles and concluded that tillage practices play a dominant role in improving or deteriorating soils.
“Even without (stover) removal,” Al-Kaisi said, “any tillage compromises soil protection from erosion.”
Based on the two ISU farm studies, he recommended that in central Iowa, no-till practices are best suited for sustaining a healthy soil profile.
He acknowledged that with residue cover and minimum tillage or no-till practices, soil temperatures will warm more slowly than with conventional tillage.
“But we found less carbon loss from soils with no-till,” Al-Kaisi said. “You cannot sustain soil quality without adding fertilizer if stover is removed.”
In general, he said if a field is struggling with yields, little if any stover should be removed.
“But if you have 200 bushels per acre,” he said, “then you should think about harvesting stover.”
However, he recommended farmers not forsake their crop rotations for continuous corn to take advantage of the current higher profitability in corn over soybeans.
“A variety of root systems,” Al-Kaisi said, “will add variety of microbes for building up the soil.”
Kapil Arora, an ISU ag engineer field specialist, based in Nevada, said the industry is still looking for the best way to harvest stover while assuring a clean and dry product available to the endusers.
“Pound for pound,” Arora said, “there’s as much stover on the field as there is grain taken from it.”
Tests are still looking for the best way to windrow and bale the stover, while limiting the amount of dirt and foreign material, called ash, in the bales.
The goal, he said, is to take 2 tons of stover per acre, but current techniques are gathering well below that weight.
Straight windrowing takes about seven-tens of a pound, and takes up less ash. Using hay rakes yields about 1.2 to 1.8 tons per acre, but there is more ash content in the bales.
Tests also compared square versus round bales and the ideal, he said, appears to be a 3-by-8-foot square bale, which can pack stover at a higher density that round. This requires a minimum 180-horsepower tractor. To get the bale weights DuPont is seeking will take a 250-hp tractor or bigger.
Towing a stover baling implement on the back of a combine, which will bale stover directly from the combine without windrowing or raking appears to be a best-fit answer for DuPont’s needs, Arora said, but it will require a high-horsepower combine, since it will have to operate two pieces of machinery and tow more weight.
Cover crops, Arora said, seem to be a good option, since it appears a grass carpet growing through stover will reduce ash content, as well as add benefits to soil.
Storage systems are also a concern, since bales will have to get out of the elements and kept dry, but this will be DuPont’s worry, and not one for farmers, he said.
Brian Anderson, an Ellsworth-area row-cropper, said the presentations showed him that he needs to evaluate each field independently, before agreeing to sell stover.
“I’m sure there’s money to be made,” Anderson said, “but I’m concerned about soil depletion.”
Ron Rethmeier, a corn grower from Laurel, said he wasn’t disappointed over what he was hearing. He said he was more interested in learning about the nutrient benefits of retaining stover on his fields, than removing it.
Unlike POET, which contracts with producers to bale and haul stover for delivery to the plant site, DuPont is contracting with producers for access to harvested fields, and hiring custom balers to harvest stover.
Andy Heggenstaller, a Pioneer agronomic research manager, based in Johnston, said this approach allows farmers to try the program without an additional chore between grain harvest and fall tillage, and without purchasing or renting the needed baling equipment.
DuPont will pay farmers on a per-bale harvested basis, limited to 2 tons per acre removed. The balers will be compensated based on the ash and moisture content of the bales.
“On average, there is 5 tons of stover per acre on fields,” Heggenstaller said. “And there’s a lot of it out there.”
By taking 2 tons, he said, it will leave enough residue to protect soil from erosion and to provide valuable organic content to the soil.
He said annually there is 800,000 acres of corn fields in a 30-mile radius around Nevada and the new plant will need the stover from just 20 percent of those acres annually. Therefore, he said, not all fields will always be harvested.
Following the meeting, he said, roughly 20 farmers indicated they wanted more information or were interested in a contract.
Heggenstaller said DuPont is also actively seeking contracts for obtaining stover.
“We sort of know who and where the interest is,” he said.
Many of those present were from outside the targeted 30-mile radius of the Nevada plant and will not be eligible for the DuPont program, Heggenstaller said.
Lignan is co-product
Unlike corn-based ethanol, with a co-product that retails as a prime livestock feed, cellulosic ethanol leaves behind lignan. Heggenstaller said there are no long-term definitive plans for how Pioneer will market the lignan, but the immediate plan is to form it into cakes and burn it. Lignan cake has a similar British thermal unit content as coal, he said. Some of it will be used to power the Nevada plan, and other out-sources maybe the nearby corn-based ethanol plant, or Ames which has a coal-burning municipal utility.
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