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Researchers Developing Single-Pass Harvester for Corn and Stover

The dual-stream, single-pass harvester. Click to enlarge. Source: Iowa State University

Researchers at Iowa State University are developing a single-pass system that will harvest corn kernels as well as the stover: stalks, cobs and leaves. The stover can serve as feedstock for cellulosic ethanol.

That dual-stream, single-pass harvesting system, based on a John Deere 9750 STS combine, was developed by Stuart Birrell, an Iowa State associate professor of agricultural and biosystems engineering, and graduate students Mark Dilts and Ben Schlesser.

Significant resources have been dedicated to the process of converting cellulose into ethanol. But very little has gone into answering how do you get a supply of stover from the field to the biorefinery. This will be critical to the success of the bioeconomy.

—Stuart Birrell

The researchers are developing stover attachments that can be used on standard combines. The result would be an additional cost to farmers of about $10,000 to $15,000 instead of the six figures it would take for a separate combine to harvest stover. The attachments would also allow farmers to harvest grain and stover with one pass through a field.

The system the researchers have come up with includes a modified row crop header and corn reel attached to the front of the combine and a chopper and blower attached to the back.

The header and reel feed leaves and stalks into the combine so the biomass can be harvested before it touches the ground and is contaminated with soil. The chopper cuts stover into 2-inch pieces. And the blower throws the chopped stover into a wagon.

Although tests with the prototype machine have been successful, Birrell said there is more development work to do:

  • Harvest capacity. The stover harvesting equipment is capable of speeds equal to a normal grain harvest when less than 50% of the stover is collected. When all of a field’s stover is collected, harvest speeds are about half of a normal grain harvest. Birrell said that would be unacceptable to farmers. Birrell is working to get the speed to at least 80% of a normal grain harvest no matter how much stover is collected. That would allow farmers to decide how much stover they want to harvest without significantly affecting the time it takes to harvest their fields.

  • Transportation. Researchers need to figure out how to pack the harvested stover so it can be economically transported. Stover comes off the combine at a density of about 3 to 4 pounds per cubic foot; it needs to be about 10 to 12 pounds per cubic foot for efficient trucking.

  • Storage. Researchers need to figure out how huge quantities of biomass can be stored. The US Department of Energy has estimated a biorefinery would need at least 2,000 tons of biomass per day. A year’s supply would cover 100 acres with 25 feet of biomass.

  • Fertility. Researchers need to determine how much stover can be removed from fields while still returning sufficient organic matter to the soil and protecting the soil from winter erosion.

Birrell’s stover harvesting research has been supported by a three-year, $180,000 grant from the US Department of Agriculture and the US Department of Energy and a two-year, $50,000 grant from Deere & Company of Moline, Ill.



Cool beans, but...

isn't this exactly the kind of R&D that John Deere, Caterpillar, etc. should be doing on their own? This isn't an advancement of theory, this is a flat-out industrial design/mechanical engineering problem. I'm not saying that its easy or cheap, but rather that it doesn't seem like it should be the work of the ivory tower.

I'm not attempting to shame ISU -- part of their role is to help the people of Iowa. I'm attempting to shame the industrial players in this market who haven't gotten the job done.


I'm not sure what the technical problem was anyway. You harvest the corn, then you cut the stover. Neither is a new process.

Combining the two steps into one pass doesn't seem all that difficult, you build a larger machine with two mechanisms. Bigger is more difficult to transport. Harvesters don't stay at one farm, they move as the season progresses.

Dual purpose machines usually don't work as well as hoped. They have to be heavier and are more complex to repair. And unless the operation is hands-free the operator will be busy keeping both working optimumly during the one pass.

You do save labor. But securing the grain quickly may be more important. The stover won't deteriorate in the field or be harmed much from storms; it can wait.

The stover harvester portion will probably 'bale' the stover and toss it over the side for later pickup. Otherwise the machine will fill up quickly.

I enjoy tossing the doubts around. But these people aren't fools and the economic tradeoffs probably make a dual machine worth trying. Or maybe the local Congressman just wanted some federal money for Iowa.

Philippe Raufast

This thing already exist in Russia for almost 40 years ! Take a look at the websites of the combines manufacturers Rostselmash or Gomselmash. Because of lack of fodder, they used to harvest also the stover. Here in France, i have seen a corn header that chop and windrow all the stover (usually it is spread all over the header width), then all you have to do is harvest the stover with a high density square baler. The bales may be treated with NH4 or urea and stored at the farm under an airtight plastic film. They can be trucked to the ethanol plant when needed. The NH4 treatment will improve cellulose digestibility (and maybe ethanol yield ?).
They call their system "single pass" but the wagon behind the combine will fill very rapidly and handling will slow down the process...


Doesn't anyone notice taking all the crop residue will leave the soil bare, and prone to wind and water induced soil erosion? A cover crop may mitigate the issue somewhat, but until they grow big/dense enough (2-4 weeks) to have an effect, much topsoil have already been lost. This is especially true since harvests tend to be during the autumn months, with the storms and winds of the season. Crops residues also slows down water, from rain, and helps the soil absorb it into the ground. This assists in recharging groundwater. Another benefit is the residues shade the soil, and decreases moisture loss.
_I am not saying all the residues can't be used, but some must remain, at least until the cover/winter crop takes over.


You don't harvest all the stover, just the excess beyond what's needed as soil cover.  This link has, or used to have, specifics.


The last I read, 50% is about the right amount of stover to leave in the field to protect the soil. We went though quite a few articles on the subject in the renewable energy news group. That is where a guy got the idea of making nitrogen fertilizer by gasifying corn stover to H2 much the same way they reform NG to H2 to make it.

tom deplume

Around here almost all the farmers have removed almost all the stover from there fields. I saw one farm where the stover had been rolled into round bales and wrapped in plastic. Don't know why yet.

Luc D'Amours

I'm presently working on willow harvesting with Agriculture&Agri-Food Canada (if you want to see a video of our prototype shredder&baler go to :
downloaded the file : saule3_20meg

Next year, we plan to work on a project to harvest a part of corn residue. I read your comments and I'm not sure what should be the right way to harvest corn residue without soil contamination :

1- Attach a large square baler at the rear of the combine (with a auxilary engine) (single-pass)
2- Install a chopper&blower at the rear of the combine(single-pass)
3- Design a corn header that chop and make a windrow and bale the residue after the corn have been removed (two-pass)
4- Other ideas...

The research funding comes from a company who want to added utilization of corn stover for medium density fiberboard (MDF)

paranay rai

serching job in c
anda opretor

pranay rai

job in canda for harvester opretor

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