Conventional wisdom suggests a corn crop be rotated with another crop. Some farmers are disregarding that sage advice and producing high yields by growing corn in the same field year after year, say two Purdue University agricultural economists.
With corn demand expected to rise, in part, because of increased ethanol production, more farmers could consider growing corn after corn - a practice commonly referred to as "continuous" corn. There are risks and benefits for producers who choose to abandon rotating corn with soybeans, says Jess Lowenberg-DeBoer and Bruce Erickson.
Continuous corn growers should expect higher production costs and will need to produce larger-than-average yields to make the cropping practice worth their while, the economists say.
Lowenberg-DeBoer and Erickson analyzed the economic feasibility of continuous corn versus crop rotation. They found that on a 3,000-acre farm in the Eastern Corn Belt with average rotational yields of 175.9 bushels per acre for corn and 56.6 bushels an acre for soybeans would have to produce at least 225 bushels an acre in continuous corn to meet those higher costs and still earn a profit.
Although several celebrated corn growers are producing continuous corn crops of 300 bushels an acre or more, university research has not shown a yield benefit from switching to long-term continuous corn, Lowenberg-DeBoer says. Field trials indicate growing soybeans after corn reduces disease and insect problems, and provides easier management of crop residue.
"If we can show that long-term continuous corn works on a general basis, then we need to be able to show a substantially higher yield from long-term continuous corn to make it competitive with rotation soybeans," Lowenberg-DeBoer says. "It may need to be as much as 50 bushels an acre more to justify the continuous corn with higher fuel and nitrogen costs.
"If we want to talk specific numbers, then we're talking about maybe $30 an acre more in nitrogen. We also have extra costs in tillage. Fall tillage is a typical part of this system, so it might cost another $20 an acre or so. All of this adds up to being, for the high-yield continuous system, costing somewhere between $80 and $100 more an acre."
The seed costs for many farmers raising continuous corn tends to be a bit higher, says Erickson, who also is an agronomist.
"They may want to plant a hybrid with particular traits that does especially well in corn on corn, while there's a broader selection in corn following soybeans," Erickson says.
"We've also noticed that people who have been successfully raising continuous corn tend to plant at fairly high planting rates -- maybe higher than would the typical producer. If you're achieving high yields planting corn after soybeans you're planting high planting rates, anyway, but there may be additional seeding costs for the high-yield continuous corn program."
The Purdue economists also found that continuous corn requires a multi-year commitment by farmers, and that producers have to think differently about crop residue and soil fertility.
"When they were raising continuous corn for a number of years, it often wasn't the second or third year but after a period of years that producers seemed to get to the point where they were managing residue and returning that residue to the field with tillage," Erickson says. "It seems that the organic matter builds up and then producers are farming in a somewhat different environment than they would if they were in a typical corn-soybean rotation or short-term continuous corn."
While long-term continuous corn poses agronomic challenges for growers, crop genetics advances, ethanol and world commodity markets are making corn on corn production more attractive to farmers in the United States, Lowenberg-DeBoer says.
"There's strong competition from Latin American countries for soybean production," he says. "There's the slow increase in average soybean yield, especially in the Eastern Corn Belt, where corn yields have been rising quite consistently and soybeans have not. The growth of ethanol demands more corn. Technology like rootworm Bt corn has made production of continuous corn easier than it was in the past.
"Another key is that in international trade, the U.S. is very competitive in corn production. If you look at U.S. corn yields compared to those in Latin America, U.S. yields tend to be twice or three times as high. These are some of the reasons why this attention to long-term continuous corn is happening right now."
And, adds Erickson, "farmers really like growing corn."
For more information about continuous corn and the Purdue economic analysis, download online, "Weighing the Returns of Rotated vs. Continuous Corn," by Erickson and Lowenberg-DeBoer.