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Continuous corn's a challenge
For the past few years, there has been a trend toward more continuous corn at the expense of the corn/soybean rotation. This year, however, it looks like that trend may turn downward, thanks in large part to high prices for fuel and fertilizer.
University of Illinois ag economists Gary Schnitkey and Dale Lattz say that between 1997 and 2005, total corn and soybean acres in Illinois have been relatively stable, but that corn's share of the total has increased.
"In 1998, the ratio of corn-to-soybean acres was 1.00, meaning that there was 1 acre of corn for every acre of soybeans," says Schnitkey.
In 2002, the ratio was 1.03. In 2003 it was 1.07. In 2004 it was 1.17. And in 2005 it was 1.27. Thus, for every acre of corn that followed soybeans last year, there was .27 acre of corn following corn.
Schnitkey says two factors can explain the shift to more corn.
"First, corn has been more profitable than soybeans," he says. "In northern Illinois, corn returns exceeded soybean returns each year from 2000 through 2004." That statement is based on Farm Business Farm Management data. He says the difference was $32 per acre in 2000, nearly equal in 2001, $23 in 2002, $62 in 2003, and $44 in 2004.
The differences were less in central and southern Illinois. Relatedly, northern Illinois has more continuous corn.
"This correlation suggests that profitability differences may partially explain corn-to-soybean acre ratio differences across regions," says Schnitkey.
The second factor behind the shift to more corn is an increase in the perceived risk of soybean production, he says. "Up to 2003, soybeans were often viewed as the safe crop since soybean yields did not exhibit as much variability as corn yields," he says. "In 2003, that perception began to change because soybean yields were considerably below trend-line yields on many farms."
The dry weather and soybean aphid damage of 2003 in the Midwest was followed by the discovery of Asian soybean rust in Southern states in 2004. Throw in the persistent problems of soybean cyst nematodes, bean leaf beetles, and sudden death syndrome, and soybeans don't seem so invincible. Plus, soybean acreage in South America increased during that period.
Furthermore, soybean yield increases have lagged behind corn yield increases. Purdue University ag economist Bruce Erickson says that 40 years ago soybean yields were typically 33% of corn yields. Now soybean yields are about 28% of corn yields.
"Some growers seem willing to accept the known risks associated with second-year corn in order to avoid the uncertain risks associated with soybean production," says Purdue University agronomist Bob Nielsen.
There's no getting around the fact that continuous corn is a challenge. Corn in a corn/soybean rotation has been compared to continuous corn in hundreds of trials. Almost invariably, the corn grown in rotation yields significantly higher.
Terry Hejny, a University of Nebraska Extension educator, says 20 years of research from 1985 to 2004 at Clay Center in south-central Nebraska shows that corn grown in rotation with soybeans yielded 6.6% better than continuous corn. Researchers typically report 7% to 10% higher yields for corn following beans in high-yielding environments such as the one at Clay Center. In low-yielding environments the difference may be far greater.