Corn stover as a new industry

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Considerable research is underway to turn corn stover from a byproduct to a co-product and earn additional value for corn growers beyond the sale of grain.

Two major in-field research projects connected with DuPont and Monsanto have very similar aspects. Questions being investigated include how much stover can be substantially removed each year, how can stover be appropriately gathered including the best equipment, what is the necessary way to store stover, are there agronomic advantages to removal of some stover and what is the value of the stover in terms of its nitrogen, phosphorus and potassium cost of replacement.

“Sustainable removal rates are going to be key, and that is a lot of what our project has revolved around. How do we harvest the stover without taking too much and then how do we use it?” said Steve Petersen, end-use market manager for Monsanto.

Monsanto is farther ahead in its research project with three years of data and working with companies, including ADM, that are interested in stover use as a feed ingredient, industrial uses (anhydrous ammonia feedstock, boiler energy feedstock, chemical ingredients, etc.) and cellulosic ethanol.

DuPont has connection to stover research through its joint venture with Danisco, a major provider of enzymes to the current corn ethanol industry. DuPont Danisco Cellulosic Ethanol (DDCE) has a cellulosic ethanol demonstration facility in Vonore, Tenn., and the stover research ties into providing feedstock for this plant and an eventual commercial cellulosic ethanol facility to be built, possibly in Iowa.

The Monsanto stover project has been focused primarily in Iowa during the past three years while DDCE’s effort was in Nebraska and Iowa for
2010.

The tremendous corn yields that are projected for coming years indicates that too much stover will be on the surface of fields, and in some cases, it already has negative consequences for farmers, especially those using no-till and minimum-till.

“The agronomic impacts are going to be key to the long-term sustainability for a biorefinery and the farmers,” said Kyle Althoff, director of feedstock development for DDCE. “Farmers are definitely interested in the impact on nutrients and soil organic matter of harvesting stover. And often we see a slight bump in yield when some stover is taken off because the soil can warm up faster in the spring, and it reduces the challenges of getting seed planted in the bed at the right depth. There are definitely potential advantages for many growers, but it has to be managed in a very sustainable way, not taking away too much organic material.”

NEED FOR REMOVING STOVER
Althoff said the first challenges are harvesting stover at an appropriate moisture level and removing the proper amount per field based on agronomic practices of each farmer. “We did a lot of work in 2010 looking at equipment performance to harvest the stover in the field,” said Althoff. The same has been true for the Monsanto project over its first three years.

“Historically, we have put hay tools in a corn field to bale stover, and that has been a challenge in itself. Just recently, we have seen companies coming out with equipment to survive working in a corn field,” said Jay Van Roekel with Vermeer Corp., who talked about the Monsanto project during the 2010 Farm Progress Show. He noted the rows and tough stalks wear out typical hay equipment.

Van Roekel explained the types of equipment being looked at for harvesting residue. Equipment companies are investigating the potential for developing new or modifying previously introduced equipment for use in corn stover harvesting. Collecting corn cobs only directly from a combine takes 15 to 18 percent by weight of corn residue off a field. Direct baling, or pulling of a baler by a combine to immediately grab the residue from a windrow, is fairly new and has been used to collect about 25 percent of the residue. Raking and then baling behind a combine with a conventional corn head has a ballpark removal of about 50 percent. And the most aggressive gathering typically removes 75 percent to 80 percent of stover when raking and baling occurs following a combine with a shredding or chopping corn head, Van Roekel said.

Matching equipment and systems to remove only the amount of stover appropriate to management targets for controlling erosion and maintaining soil organic carbon is part of both research projects.

PARTIAL HARVEST AND STORING
A look at “partial harvest” was part of the Monsanto project for 2010/2011. Petersen noted that a field might have an average slope of 4 percent, which would make it unharvestable because the stover is needed for erosion control, but parts of that field might be flat and other parts at a 7 percent slope.

“If you did a report on some of these fields and you took the average, then you wouldn’t harvest any of the ground. But what we found is that 50 to 60 percent of the area of many fields were harvestable, if they are done in the correct way,” Petersen said.

More emphasis than ever was put on storability of corn stover this year as part of the Monsanto project. Round bales have been the common stover gathering method, but square bales have some intriguing transportation and handling advantages; therefore, two stacks of about 750 bales each of 1,000-pound square bales were stacked under tarps. A total of 72 heat monitor sensors were imbedded in the stacks to measure how well the corn stover is storing.

“Farmers are going to be able to bale this material, but how do they store it? Can they store it for long periods; what is the degradation; is there dry matter loss; what happens if there is a wetter bale in the middle of a pile?” Petersen said in explaining the questions he is trying to answer.

“We’ve had some really interesting results considering even how dry it was last year. The piles have warmed and certain bales have heated in some cases,” said Petersen. “We connect a computer to the monitors and pull the data monthly to update us on what has happened in the pile.”

Bales stacked at the edge of a field appear to be the most logical answer for the huge volume of material that will be needed for any use, whether it be as a feed ingredient for mixing with dried distillers grains or cellulosic ethanol production. Neither research project has ruled out under-roof storage as being necessary. Hoop roof facilities were one of the options looked at by DDCE for the 2010 stover.

Petersen said most processors would prefer dryer stover, with moistures of 10 percent to15 percent. “We’ve seen this in some fields where the stover had two to four days to dry out after the corn had been combined. With the long dry fall this year, we had an average harvest moisture of 13.5 percent. However, moisture levels were much higher in the rainy, delayed harvest seasons of 2008 and 2009,” he said.

He also said the upper limit for stover storage is higher than hay, perhaps as high as 20 percent, but this will probably depend on how the stover is stored, and it is something still being investigated.

ADDITIONAL CONCERNS
A big part of the Monsanto project has been focused on the nutrient replacement value or cost to the farmer to replace N, P and K removed with the stover. Three years of data indicates an average of 16.3 pounds of N, 5.4 pounds of P and 18 pounds of K is being removed per dry ton of material removed in the project fields of Eastern Iowa. Using Iowa State University supplied fertilizer costs, the three-year average cost for replacement fertilizer would be slightly less than $10 per large round bale, Petersen reported. These values could be considerably different in other soil types or fields with higher P and K levels.

Althoff said a commercial cellulosic ethanol production plant would require stover gathered from between a 30- and 45-mile radius. Of course, that is why locating a plant in a corn-dominated production area is mandatory to minimize transportation and assure feedstock. “We don’t want to be constrained in our potential supply of stover,” he said.

“We are also looking at how we manage inventory risk from year to year and thus being able to carry over some stover inventory from year to year to mitigate risk,” Althoff said. That makes solving any long-term storage issues a prime consideration.


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