Growing Energy Crops

Conservation tillage proponents have long regarded crop residues as a treasure.  Now, the energy industry is catching on, too.  Growing interest in converting plant material to energy could open new profit opportunities to farmers – but it could also create a tug-of-war over crop residues, pitting potentially profitable energy markets against long-term improvements in soil quality.

Bales of switchgrass residue stand in the energy crop at David Wilson's Alabama farm. Photo courtesy of Marie Walsh

Of course, the simplest way to get into the energy market is to sell corn to one of the 95 ethanol refineries in the U.S. or soybeans to one of nearly three dozen biodiesel refineries in the country.  The situation becomes more complicated as energy engineers set their sights on harvesting energy from crop residues or biomass crops, like switchgrass or johnsongrass, which can be harvested like hay and burned with coal, or processed to create ethanol.  In fact, ethanol from residue is especially appealing because it can burn with fewer greenhouse gases and contain a greater net energy balance than ethanol from grain – 25,000 Btu/gal for ethanol from corn grain vs. 60,000 Btu/gal for ethanol from corn stover.

At the USDA National Soil Survey Center in Lincoln, Neb., conservation agronomist Dave Lightle takes a cautious approach to the idea of residue removal.  He quotes renowned Chilean no-tiller Carlos Crovetto – “Grain is for the farmer; residue is for the soil” – to warn of the importance of crop residue in rebuilding the nation’s lost organic matter and protecting the soil from erosion.  But he acknowledges that on the right fields, in the right rotation, some residue could be harvested and sold sustainably.

Removing Residue

Corn stover shows promise as a feedstock for producing ethanol or other chemicals.  It’s not as easy to convert into ethanol as grain is – the cellulose in corn stover must be broken down with acids or enzymes before the resulting sugars can be fermented into alcohol – but the technology is improving.  As a result, the cost of producing a gallon of cellulosic ethanol has dropped from $5 to $1 over the past 25 years, according to the Ag Marketing Resource Center at Iowa State University.

Producing ethanol from crop residue requires a different type of refinery than the ethanol plants that have been springing up around the country, notes Marie Walsh, adjunct associate professor at University of Tennessee and former biofuels researcher at the U.S. Department of Energy’s Oak Ridge National Laboratory.  With a price tag of $300 to $400 million for a plant that can process 2,000 tons of corn stover a day, “that’s not going to be the kind of thing that’s going to be popping up all over the place,” Walsh points out.

But some growers may see a market for residue emerge.  When they do, conservation tillage will provide an important edge.  Walsh worked with NRCS’s Lightle and Kansas State University agricultural engineer Richard Nelson to determine how much corn stover could be removed from a field while still controlling erosion.  “With conventional tillage in most places, you can’t take much off,” she says.  “You need to shift to reduced tillage or no-till – then you can remove greater quantities.  But controlling for erosion might not be enough – you still have to consider the impacts of high removal rates on organic matter levels.”

Harvesting Stover

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In Harlan, Iowa, grower and biomass broker Tom Schechinger spent several years providing thousands of bales of corn stover to horse bedding processors in Illinois and Wisconsin, a hydro-mulch company in Iowa, and a local chemical plant that converted it into an industrial chemical called furfural.  He believes there’s a future for stover harvest.

Harvesting stover isn’t very complex.  About two weeks after grain harvest, Schechinger came through the field with a round baler outfitted with a flail head attachment.  The flail chops stalks on the ground and cuts stalks that were crimped by the combine’s snapping rollers.  How low and how early the chopper/baler was deployed was determined by the customer’s tolerance for moisture and dirt (both of which increase as the stalk is cut lower).

Schechinger says residue removal can be a big plus for conservation-minded growers in the northern Corn Belt, replacing the desire for tillage with a potentially lucrative market.

“A lot of the reason for tillage in the northern Corn Belt is because when you have so much plant material, you can’t get your ground to warm up in the spring to plant, or get it to dry out enough so you don’t cause compaction,” he points out.  Investing some of the proceeds of the sale of corn residue from the field – which can be in the range of $50 per ton – a grower could easily seed a cover crop to protect the soil over the fall and winter, Schechinger says.  Levels of residue left behind can also be adjusted to meet field needs by adjusting chopping height or by skipping rows when baling.

Switch to Switchgrass

Near Lincoln, Ala., grower David Wilson spent eight years producing switchgrass for a nearby power plant that ground it up and burned it with coal.  A native perennial that produces stalks up to 10 feet tall and sends down a root system to match, switchgrass is a dream biomass crop.  A stand can be established with a no-till drill and last for years, eliminating the need for annual fieldwork, and yields can be enormous – Wilson says he harvested eight tons per acre at his field’s peak, pointing out that his switchgrass was planted on “very, very marginal pasture land.”

But there are challenges, too.  “When you put eight to 10 tons out on the ground at one time, you can’t dry it out,” Wilson warns.  “You’ve got to limit how much is on the ground.”  He switched from a single harvest to two cuttings per year, which helped him manage the volume of biomass and reduced the number of flat tires he suffered while driving over the sharp points of mature, woody stems that had been cut by his mower-conditioner.

Wilson followed his mower-conditioner with a round baler that wrapped each bale in mesh.  “I tried to dry-chop it as silage, but it eats the chopper blades up faster than you can sharpen them,” he notes.  “It’s like you put rocks through it.”  On a modified 53-foot dropped-deck trailer, he could stack 42 bales for the 60-mile haul to the power plant.

Though the pilot project that funded research into switchgrass burning at the Alabama plant ended, taking his market with it, Wilson is optimistic about biomass crops.

“It’s not a get-rich-quick thing, but I do believe that at $50 a ton, if we could keep transportation costs down, it can be profitable,” he says.  “You can raise it and not have to do any tillage and not have to buy that $350,000 combine, and you’re not going to have to plant it every year.”

Wilson emphasizes that transportation is the make-or-break factor in the equation.  “Don’t get into something if you’re going to be hauling it more than 50 miles,” he warns.

The market for switchgrass is a big unknown.  If the economics line up and the energy industry invests in co-burning or cellulosic ethanol production plants, the sky’s the limit.  In fact, one USDA study found that a price of $40 per ton could make switchgrass so profitable that it could inspire growers to produce enough switchgrass to produce four times as much ethanol as was distilled in 2005.  A great deal of investment and infrastructure would have to emerge first – but if and when it does, switchgrass promises to be a natural choice for many conservation-minded producers.

Future Considerations

It may be quite a while before investors build a $400 million ethanol plant within 50 miles of most farms.  But that time may come – and with high energy prices, governmental mandates and incentives to expand renewable fuels production, and a ready supply of feedstock, it may come sooner rather than later.

 Lightle at NRCS offers some tips for growers ready to try the biomass market:

• Biomass crops are more conservation-friendly than residue removal.  “The key is ‘perennial’ so you don’t have annual tillage,” Lightle says.  “Switchgrass has a tremendous root system pumping organic matter back into the soil.  Over the long haul, it’s probably not detrimental to organic matter levels.”
• Stay off of highly erodible land.  “That land’s already got dibs on that residue,” he notes.  “If it’s highly erodible land and you’ve got a compliance plan that calls for certain levels of residue, you’re probably not going to want to take any off.”
• Be careful on good ground.  “On level or highly productive land, harvest only the amount of residue to maintain tolerable soil loss levels and existing organic matter levels,” Lightle advises, noting that local NRCS offices can help establish those levels with Soil Conditioning Index models.  Stick to harvesting abundant residue like corn stover or wheat straw, he adds; don’t harvest residues from soybeans or cotton, which don’t offer much to begin with.
• Replace lost nutrients.  “We’ve got to consider the fertility of what’s being removed for biomass,” Lightle reminds growers.
• Consider cover crops to replace biomass that’s been removed.  “Cover crops are viable where adequate moisture exists for such crops, but in the western Corn Belt and other drier areas, we don’t have enough precipitation for a regular crop and a cover crop,” he cautions.
• Reduce tillage to make the most of the residue left behind.  “If at all possible, move to tillage systems that have very few disturbing passes,” he says.

Great Potential

In Iowa, Schechinger says selling stover could change the way growers think about corn.  “People will start looking at the whole-plant value of their crop rather than just the grain value,” he predicts.  Growers may choose different varieties and plant higher populations in an effort to optimize the output and balance of stover and grain, rather than pumping the crop for high grain yields.

But UT’s Walsh adds a cautionary note, warning growers to get a contract in hand before committing to a biomass project.  “While biomass has a great deal of potential, that potential has yet to be realized,” she notes.  “Don’t jump into the water head-first without first finding out how deep the water is and whether there are any rocks on the bottom.”

Lightle sees potential, but keeps his eye firmly on the ground.  “It’s not rocket science,” he says, “but it does take some thought so we don’t make a fast buck at the expense of the soil.”