ANALYSIS - Residue buildup has become a big challenge for growers, but partial corn stover removal could not only improve stand establishment and yield, it could also offer additional income, writes Sarah Mikesell, TheCropSite senior editor.
Dupont plans to build one of the world's first commercial cellulosic ethanol biorefineries in Nevada, Iowa, USA, which will require thousands of tons of stover from Iowa corn fields.
"Currently, the most plentiful agricultural source of ligno-cellulosic biomass for ethanol production in the US is corn stover," said Mr. Steven Mirshak, DuPont Business Director of Cellulosic Ethanol. "We're working with an exclusive group of growers in a pilot program to collect stover in support of the biorefinery. When completed, the plant will be fueled almost exclusively by cornstalks."
DuPont has purchased land from Lincolnway Energy, a corn ethanol plant in Nevada, Iowa, and expects to break ground in the second half of 2012. Construction is expected to take 12-18 months.
Cellulosic ethanol is a second-generation advanced fuel produced from grasses and non-edible parts of plants. The key to cellulosic ethanol is the lignin cellulose component in a plant, which provides structure to the corn stalk and contains lignin cellulose and hemicellulose.
Why is Cellulosic Ethanol Important?
Energy independence is an important issue for the United States.
"You see the Straits of Hormuz now in our issues with Iran, and there are a lot of threats occurring, and oil prices are increasing," Mr. Steven Mirshak, DuPont Business Director of Cellulosic Ethanol, said. "So developing a transportation fuel supply that's not petroleum-based is critical. Corn ethanol has been a great development; it's about 10 per cent of the fuel supply, and advanced biofuels are the next generation."
Greenhouse gas emissions are greatly reduced with cellulosic ethanol. The federal government standard is a 60 per cent reduction versus gasoline as a minimum, and DuPont will be well below that in their Nevada plant.
Part of the demand is driven by the US government's mandate for renewable fuels, the Renewable Fuels Standards, which is part of the Energy Independence Act, and recognizes the need for the US to develop our transportation fuel supply.
"We can go up to about 15 billion gallons of corn ethanol in the fuel supply, and that levels off because we're at that capacity in the US today," he said. "On top of that, we have the mandate to add 21 billion gallons of advanced biofuels. This will require 160 million to 200 million tons of feed stock, that's a lot - some of which can be corn stock."
The government mandate requires 16 billion gallons of cellulosic ethanol be produced in the US by 2022.
"We need many, many companies to participate in that investment, and it's a broad collaboration," he said. "Our business model is to have participation in a number of plants, but we'll license the technology broadly. And this is very important, as we want to get many participants in building cellulosic ethanol plants across the Corn Belt and based on energy crops in the South."
The process starts first with feed stock supply, so corn stover is collected and pre-processed, by grinding it up into small particle sizes. Those particles go through a saccharification process and are pre-treated. Then the process is to separate the lignin, the cellulose and the hemicellulose.
"We have proprietary technology we've developed to do that, which we believe gives us a very strong advantage. We then saccharify the cellulose and hemicellulose - the sugar," Mr. Mirshak said. "We ferment it, which produces the ethanol, and then we have a separation process. We have a lot of co-products that we use to generate the energy that fuels the plant."
Stover Collection & Management
DuPont sets up contracts with farmers in a 30-mile radius of the plant that allows access to land after farmers have combined their fields. Then DuPont's team goes on-farm and manages the collection of all the stover themselves.
The first step is to windrow the excess stover into rows on the field and then bale the stover into large, rectangular bales. The bales are then stored at a number of large storage sites around the Nevada plant until they are fed into the processing plant.
"We designed our program to be very focused on how we improve yields by removing stover, and improving the efficiency of stand establishment," he said. "Once you get to about 170 bushels an acre, you have about 4 tons of stover on the field. That's the average in the Nevada area. As corn yields continue to increase, stover residue will also continue to increase."
Today, tillage is the primary means of managing residue on the field. However, tillage has some negative consequences, essentially the introduction of oxygen into the ground, which reacts with the organic content, to have a negative impact on the organic content in the soil.
"Partial stover management will allow for residue management with reduced tillage. Stand establishment is a critical issue," he said. "We anticipate faster soil drying times in the spring and warming in the spring, and improved uniformity of seed placing, reduced pressure on disease, and reduced nitrogen tie-up. University studies with partial stover removal have demonstrated a significant yield advantage can occur."
Feed Stock Availability
A US Department of Energy study done at Oakridge National Laboratory estimates there's about 235 million tons of feed stock available today, and a significant portion - about 40 per cent - is agriculture residue - and about 80 per cent of that is corn stover.
Looking longer term, Mr. Mirshak believes corn yields will continue to increase the amount of corn stover available for cellulosic ethanol production, making corn residue an important component of the next generation of biofuels in the US.
DuPont's sustainable harvest goals are focused on three critical areas:
- Management of soil erosion
- Managing soil fertility
- Sustain organic matter
The team focuses on a field-by-field basis to make sure we have a sustainable harvest rate. The frequency depends on the yields in the field, the slope of the field, and production practices. Once they've studied the field and compared or data, then it's time to determine what is the appropriate amount of stover to remove from the field and what is the appropriate harvest rotation.
"We will not remove stover from every field, every year," he said. "It's a careful, sustainable focus in terms of making those determinations."
Important to remember, this is partial stover collection, and the amount left in the field will vary.
"We're not leaving a field barren; the field is still managed very carefully, making sure we're putting the proper amount of organic matter back into the field, managing the soil erosion and the nutrient value," he said. "We collect at most, 50 per cent off of a field, so two tons/acre is our goal for a field. We focus on high-yielding fields where that stover has been generated."