Bales of corn stover surround a tent set up for a ceremony at the site of DuPont's new cellulosic ethanol plant in Nevada, Iowa, which is under construction. The company plans to harvest stover from 190,000 acres when the plant is fully operational in 2015.
Even in early December, an occasional truck still hauled loads out from some central Iowa corn fields. The loads didn't contain grain, but stover — the leaves, husks and cobs left behind after the grain was harvested.
Stover bales are big, heavy and cumbersome. But they have new value now thanks to commercial-scale cellulosic ethanol production. Two plants are under construction in Iowa, plus another is going up in southwest Kansas. The Abengoa Bioenergy plant in Hugoton, Kan., will also use other biomass feedstock, such as wheat straw and milo (sorghum) stubble. But in Iowa, the ubiquitous feedstock is corn stover.
Farmer Bill Couser of Nevada, Iowa, said the combination of higher yields from modern hybrid seeds and the government’s Renewable Fuel Standard makes Iowa a great place for cellulosic ethanol production.
“Right now we have an abundance of organic matter” after harvest, Couser said. To cope with that, farmers have been using more fertilizer, which potentially adds nitrogen runoff to waterways. Now, instead, they can actually sell the excess biomass.
“When you look just at the environmental side of it,” Couser said, “to be able to use less fertilizer to grow a crop — that’s in everyone’s best interest.”
Couser implied that the fact that farmers get paid for the stover was almost an afterthought. He also pointed out that no one wants to remove all the stover. In fact, several years of research have gone into determining the optimal amount to remove, and the consensus seems to be about 20 percent of the above-ground biomass. Of course, you only have so long to get it.
“The key challenge from a feedstock perspective is to gather all of the stover that we need to operate a plant for an entire year in a window of approximately 35 to 40 days,” said Andy Heggenstaller, an agronomy research manager at DuPont Pioneer in Johnston, Iowa.
Heggenstaller has worked with farmers in the area surrounding DuPont’s new plant. One of the key considerations is storage. Despite its newfound market value, stover is still what Heggenstaller calls a “low per-unit value” commodity, so it’s not economical to store it in buildings, for example. Instead, the large bales are stacked neatly, covered tightly with tarps and scattered to various storage locations.
“We’ll keep a little bit of it in a lot of different places to minimize the risk to any one location being lost or damaged somehow,” he said.
Some of this year’s harvest is already being stored (some went to a research plant in Tennessee) and all of the 2013 stover harvest will be stored for use in late 2014 when the plant comes on-line. Eventually, Heggenstaller anticipates harvesting stover from 175,000-190,000 acres each year in central Iowa, for production of 28 million gallons of cellulosic ethanol annually.
Couser said it’s important to note that stover harvest won’t happen year after year on the same land.
“There’s a cycle they go through,” he said, that might be a stover harvest every other year or every third year.
Agronomy researchers at Iowa State University are working with farmers and industry, Couser said, to figure out “what is the proper way to handle this? To manage this? To manage the land? And then to educate the farmers that are involved in this so that, long-term, everybody’s on the same page.”