The 2010 season was a disappointing one for corn growers in many parts of Illinois, says University of Illinois Extension agronomist Emerson Nafziger. With a statewide average yield of only 157 bu./acre, just 4.2 bu. higher than the U.S. average, and the third-worst yield in the past decade, many Illinois producers are hoping for a more bountiful 2011.

Over the past 10 years, the Illinois corn yield has averaged 13.7 bu./acre above the U.S. national average, and has been below the national average only once (by 4.9 bu. in 2005) and above it by as much as 25.1 bu. (2008).

“The major problem in 2010 was heavy rainfall in June that resulted in standing water and saturated soils, which in turn resulted in nitrogen (N) loss and damage to root systems which could not be repaired,” Nafziger says. “As a result, affected fields and parts of fields ended up with shortages of both N and water, problems made worse by high temperatures and early maturity, and in some cases by dry weather during the latter part of the grainfilling period.”

Corn following corn was particularly hard hit in 2010, and there were numerous reports of larger yield penalties for corn following corn compared to corn following soybean than most have seen for a number of years, he adds.

In research trials conducted since 2003, Nafziger saw similar results. He has been comparing continuous corn, corn rotated with soybean, and corn following either corn or soybean in a corn-corn-soybean rotation.

Nafziger says that the rule of thumb for many years has been that corn following corn yields about 10% less than corn following soybean. This difference has often been less than that in some recent comparisons, but he said it varies depending on the year.

Across four northern Illinois sites, the yield penalty for continuous corn was about 11% in 2008-2009, but 19% in 2010. Second-year corn in the corn-corn-soybean rotation yielded only 5% less than corn following soybean in 2008-2009, and 10% less in 2010, indicating that having soybeans even two years ago helps lessen the yield penalty for corn following corn. At the two southern Illinois locations, with considerably lower yields, the penalty for continuous compared to rotated corn was substantially less, measured either as bushels or as a percentage, he notes.