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Corn stover provides bright prospects for feed, fuel

March 18, 2014 | 0 comments


Corn stover is gaining ground as both livestock feed and biofuel feedstock at a rate that appears sure to accelerate.

With ethanol plants that use stover coming on line and farmers turning to the substance as economically-viable cattle feed, the acreage is expected to jump, predicted Dennis Pennington, Michigan State University senior bioenergy educator who spoke during the March 2014 field crop production and pest management webinar hosted by Michigan State University Extension.

In 1970, before the advent of biofuels and biotechnology, not quite 67 million acres of American land were planted to corn. Producers were growing 18,000 plants per acre in 38- to 40-inch rows and reaping, on average, 72.4 bushels per acre for a total U.S. production of 4.15 billion bushels. There were no biotech traits available for corn.

In 2010, over 88 million acres were planted to corn with yields doubling to almost 155 bushels per acre for a national yield of 12.5 billion bushels. Producers were growing 30,000 plants per acre with row spacing of 30 inches. Now, over 85 percent of corn acres have biotech traits.

In 2030, it is projected that 100 million acres of corn will be planted that could yield 300 bushels per acre, on average, for a U.S. harvest of more than 30 billion bushels. Planting densities will jump to around 45,000 plants per acre and row spacing will shrink to 20-30 inches. There will be 15 to 20 biotech traits available, and growers will probably be able to customize their hybrids to fit their farm and fields best.

Challenge or opportunity

The amount of corn stover in a field increases its grain yields increase. Calculations put the harvest index at 58 percent for current hybrids, meaning a 200-bushel-per-acre field will produce 4.8 bone dry tons of grain per acre and 3.4 bone dry tons of stover per acre to deal with.

"The question is should we leave it or remove it," Pennington said.

Comparing pros and cons, Pennington said the positive effects of removing stover are soil temperatures warm more quickly in the spring; there is improved soil-to-seed contact; more even planting depth and spacing; and disease levels may be reduced.

The negative side includes potential long-term effects on soil organic matter and increased erosion by wind or water, while the removal of nutrients means growers will need to apply more fertilizer.

The winning argument is that stover left on a field reduces wind and water erosion and provides soil organic matter, which enhances soil's water and nutrient holding capacity. Higher soil organic matter means less crusting and compaction, and promotes higher crop yields.

"Stover removal must not compromise soil quality; it is required to maintain soil health," Pennington said. "We cannot remove all stover from all fields every year."

Soil carbon is a critical metric for how much stover can be removed from a particular field. Less stover can be removed in corn-soy rotations than from fields in continuous corn.

Studies on how much stover can safely be harvested found that reducing the amount of tillage bumps up the amount of stover a grower can utilize. For example, if a Wisconsin grower's total available supply of stover was 8.1 tons per acre, 1.5 tons of stover could be harvested with conventional tillage. If the grower converted to mulch tillage, he could take 2.2 tons per acre, and if he converted to no-till, he could take 4.1 tons.

Stover as feed and fuel

Feed is 63 percent of animal cow cost, of which 64 percent is winter feed costs. Drought has helped tighten the margins for beef producers over the past five to seven years, Pennington said, noting beef cow hay prices are currently $150 a ton. "Quite a few places have gone out of business," he noted.

Besides animal feed, biofuel plants are another reason to harvest stover. The plant in Abengoa, Kan., which will produce 25 million gallons a year of cellulosic ethanol, needs 1,000 tons of stover a day. In Iowa, the DuPont/Pioneer plant, to produce 30 MGY, needs 375,000 tons of stover a year, while the Poet DSM plant in Iowa, producing 25 MGY, will need 350,000 tons of stover a year.

"Add it up, and you need about a million tons of stover just to supply those three plants; that's a lot of stover," Pennington said, pointing out that 500,000 acres of corn are needed if two tons of stover are removed per acre, while 333,000 acres would be required if three tons were removed per acre.

There is definite need for stover to use as animal feed and biofuel, and more is being produced, Pennington said.

Harvesting stover

For stover harvest, cut or shred the corn stalks only if necessary, and rake, depending on the stover's moisture levels and equipment.

Corn grain harvest equipment can now be a one-pass deal that takes the grain off; cuts and chops the stover; and, with the chaff spreader removed, deposits the stover in a windrow to dry.

Newer technology, in the form of specialized equipment, is also available. At the Ohio Farm Science Review, a corn rower head caught plenty of attention, Pennington said. It has bolt-on attachments with two spinning knives that cut and chop the stuff up and blow it back to a conveyor that moves it to the center of the combine to make a good solid windrow.

If the combine windrow is the only stover harvested, the yield would be 2.4 bales per acre or 38 percent of the available stover. With the combine windrow and raking, 4.3 bales per acre could be harvested. That's still only 52 percent of the stover out there. "Some of the equipment is not physically capable of removing all of the stover, even if we wanted to," Pennington said.

Stover harvesting challenges

Keep in mind that weather conditions are a critical factor when harvesting stover. In the fall, after the grain is off, there can be as few as nine days to get the stover off before snow starts flying, Pennington said.

Another challenge is what sort of equipment to put together in terms of combine, flail choppers, rake and baler. "Before you go invest, figure out what's best for you," he advised.

Also, consider storage methods, transportation and the product's value on the farm. For example, a study measured dry matter loss on round bales stored eight months. For dry bales (less than 25 percent moisture), there was a 3.3 percent DM loss with inside storage; a 10 percent loss on bales stored outside in nets; 13.9 percent loss with plastic twine; and a whopping 30.4 percent loss with sisal twine. "I had no idea sisal twine was that terrible if you stored outside," Pennington said.

With wet bales measuring over 45 percent moisture, there was a 2.9 percent DM loss for bales stored outside in plastic wrap. For chopped stover silage over 45 percent moisture, the DM loss for outside storage in plastic bags was 5.4 percent.

Corn stover economic value

Considering the value of a bale of corn stover's nutrients minus the costs of field operations including mowing, raking and baling, one approach worth considering is to harvest stover every two or three years at 3 tons per acre, rather than a ton per acre per year. That could be more efficient in terms of economics than running the equipment around the field every year, Pennington said.

Studies of corn stover compared to average alfalfa/grass hay found the key difference is crude protein, which averages 4.5 percent for stover compared to almost 13 percent for hay. Cattle feed cost comparisons conducted at Oklahoma State University found savings with stover over hay of $.71 per head per day for a savings of $128 per cow over 181 days. With a 35-head herd, that means winter feed savings of over $4,450.

Managing protein intake

Pennington advised producers to make sure they use ration-balancing software and to rotate the hay and corn stover feedings.

"If you feed them together, the cattle will leave the hay and go stand by the corn stover and beller at you to bring them more hay," he said.

It is critical to meet the protein requirements of mid-gestation of 120 days-plus pregnant through early lactation for adequate calf immune system development and colostrum production. Pennington recommended a schedule of alternating hay and stover for early- to mid-gestation cows. From mid- to late-gestation, feed two-thirds hay and one-third corn stover, while late-gestation into early-lactation cows should be fed all hay.

A study at Iowa State University on feeding cattle calcium-treated stover found it took a bit less feed to put the same amount of pounds on. The bottom line was feeding calcium-treated stover didn't improve the efficiencies, but it did reduce the cost of getting the feeder to market, Pennington summarized.

Corn stover harvest project

As stover rises in importance, a group of corn growers, livestock producers, researchers, extension personnel and industry members have joined together as the Corn Stover Harvest Project Team. "We see the potential and want to get on the front end," Pennington said. "The question is what do we do sustainably, yet get some benefit out of the stover."

The team has developed six different objectives, including corn stover harvest, a storage study, feeding trials, market development and cover crops. Funding has been requested, and a corn rower has been leased for the project, which will focus on applied research on farms.

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