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Corn after corn takes more intense management

If you can’t “lick them,” why not help them find a better way?

That’s basically what Roger Elmore and other Iowa State University corn specialists decided last winter after growers kept asking questions about planting corn following corn as prices rose above $4 per bushel.

“After I came here in July 2005, it seemed the question most frequently asked was how to grow corn on corn,” said Elmore. “We started talking about the problems with that, but it became obvious farmers were more interested in solutions than hearing the problems.”

It’s easy to see why Iowa growers would be interested in corn on corn. With prices still hovering around $4, farmers were expected to plant another 1.3 million acres of corn this spring, bringing the state’s total to 13.9 million acres. That’s a million more than the next largest corn-growing state, Illinois.

Mid-South farmers generally rotate corn with cotton and other crops, but they could become more interested in continuous corn if prices remain high. Still, they should be aware of the downsides, specialists say.

Research and Extension specialists at Iowa State talked about how to overcome those throughout the winter. They also published a 40-page special edition of their monthly Integrated Crop Management newsletter that was devoted entirely to continuous corn production.

For Iowa farmers, planting more corn is not just an agronomic issue, according to Elmore, an agronomist at the University of Nebraska before moving to Iowa. Many are also shareholders in the 27 ethanol plants currently in operation in the state. (At least 30 more are under construction or in the planning stage.)

Researchers expect Iowa’s corn yields to continue increasing at the national average rate of 1.75 bushels per acre per year. “But this will not come close to meeting the future demand for grain,” said Iowa State specialist Lori Abendroth. “The only way to meet the demand is to increase acreage devoted to corn.”

This won’t be the first time Iowa has had this much corn. “In the early 1980s, we had the same number of corn acres we have now,” said Elmore. “Then our soybean acres started to go up and corn had leveled off in recent years.”

Iowa agronomists expect soybean plantings will be down about 950,000 acres this year with the remaining 400,000 of the 1.3-million-acre increase in corn to come from the Conservation Reserve Program.

“When we started telling farmers they could lose yield from following corn with corn, they weren’t happy with us,” said Elmore. “But when you plant corn on corn, you have more residue, more nitrogen demand and more disease potential. All that can reduce corn yield.”

Fortunately, research at other land-grant universities confirmed the Iowa State findings on corn following corn.

Mike Duffy, an Iowa State University agricultural economist, has also developed a yield calculator to help farmers determine how much of a yield penalty they might incur with corn on corn.

“Most of the research shows a yield loss of 5 percent to 10 percent,” said Elmore. “But farmers can plug their own numbers into the yield calculator. The cost of nitrogen is one of the major variables.”

Iowa State has developed two spreadsheets that allow growers to analyze the most profitable rotation to follow. One lets the grower enter the level of nitrogen used and the other uses the level of nitrogen that would be optimum as determined by the ISU Maximum Return to Nitrogen calculator.

Under average conditions with $6.50 soybeans, a corn/corn/soybean rotation is most profitable at around $3.50 per bushel for corn while a corn/corn rotation is most profitable at $3.80.

Elmore has been an advocate of diversified agriculture for most of his career; so working on corn on corn did not come easy to him or many of the other research and Extension specialists.

“I’ve traveled in Argentina, and that was a real eye-opener,” he said. “Their rotation strategy when I was there was to have two or three years of pasture followed by a year of corn and a year or two of soybeans. They’ve gone away from that and their yields have suffered somewhat.”

Continuous corn can bring a host of other problems beyond dealing with more corn residue, he said. Repeated cropping of corn may also cause corn nematode populations to flare up. Most of these pests such as dagger and needle nematodes are native to Iowa but could be transferred to the South as corn equipment moves in this direction.

Iowa State research also shows the nitrogen fertilizer rate requirement can be an average of 50 to 60 pounds of N higher with corn followed by corn than with soybeans followed by corn.

Thus, the recommended N application rate for corn following soybeans would be about 125 pounds of nitrogen per acre and for continuous corn 175 pounds of nitrogen per acre. (Iowa State gives a rate range of 105 to 145 pounds for corn following soybeans and 155 to 195 pounds for corn behind corn.)

For farmers rotating cotton and corn, growers should check their state fertility recommendations since cotton producers would not receive the “nitrogen credit” from growing soybeans.

Selecting the right hybrid can be an important step in minimizing the “yield drag” from continuous corn, says Elmore.

“Look at the hybrids at the top of the list (on university or other third-party trials),” he said. “This is critical. If you start with a poor performing hybrid, you’re cutting your chances of maintaining yields.”

Growers should compare yields from a number of locations, said Jim Rouse, an agronomist who oversees the hybrid-testing program at Iowa State University. One mistaken belief: Hybrid data from a field near your farm may be more useful than a field far away.

“Some people point out that hybrid rankings will differ between a corn-following-soybean site and a corn-following-corn site,” Rouse noted. “But the missing information in this scenario is that hybrid rankings also differ between various corn-following-soybean sites and between corn-following corn sites.

“This variability is caused by the hybrid/environment interactions. Because of the unpredictable nature of the interactions, and because you cannot predict the weather, it is prudent to select hybrids that will perform well regardless of the environment.”

Elmore notes that Rouse typically conducts corn hybrid performance trials at 20 to 22 locations around Iowa. Hybrids are tested both for yield and for risk management factors such as maturity, seed treatments and transgenic traits.

“Pioneer, DeKalb, Syngenta and Dow Mycogen also are conducting testing, and these companies are not going to sell you a bad hybrid,” he said. “But farmers owe it to themselves to look at third-party, unbiased testing. The companies have a product to sell, and their advice may be good. But couple that with objective information.”

Transgenic traits can also be important features, but the traits will probably not increase yields. “My son is on the track team at his high school, and he can run the 100-meter dash in 11.3 seconds,” says Elmore. “A transgenic trait might take us to 11.19 seconds, for example, but it won’t get us to 11.0.”

Genetics can help boost yields, he said. But it has to be part of the whole package.

“Kip Cullers, a farmer from Purdy, Mo., produced the top yield in the 2006 National Corn Growers Association contest with a Pioneer hybrid that could be purchased by any farmer,” he noted. (Cullers also harvested a world record soybean yield of 139 bushels per acre in 2006.)

Elmore said he’s been receiving telephone calls from Southern growers who have told him, “This is the first time I’ve grown corn in my life.”

He cautions them to start with the whole package and not focus on any single production aspect. “No one thing is going to get you to the Kip Culler stage,” he noted. “Our average yield here in Story County, Iowa, is 166 bushels per acre, and no one thing will get you to the county yield or to 200 bushels per acre.

“Certainly, hybrid selection is important, but so are planting dates, plant populations, row spacings, fertility rates, tillage practices, insect management and weed control. All these tend to be factors in producing or protecting yield.”

While 30-inch row spacings have received a fair amount of attention in recent years, Iowa State research has not shown much of a yield advantage for 30-inch rows, says Elmore. “The data shows farmers get more response from narrow rows as you go north.”

Much of the yield gains of recent years seem to be coming from increasing plant populations. Farmers in Iowa have been on an upward trend with seeding rates, going from around 28,000 seed per acre in 2001 to 30,000 to 31,000 seed per acre in 2005. (Most farmers use a slightly higher rate for corn following soybeans than corn on corn.)

“I don’t think it would be any surprise that Kip Cullers plants 55,000 seed per acre in his yield contest fields,” said Elmore. “Other contest winners have been in the 40,000s, which is 10,000 to 20,000 more seed than most of our farmers are planting.”

Farmers who can irrigate corn, like Cullers, have an advantage over dryland producers. “Water is certainly a big factor,” said Elmore, “but, when you can irrigate, you add another element of complexity to your production.”

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