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.
2011 field conditions
Despite the relatively poor performance of corn following corn in 2010, Nafziger says most indications are that this shouldn’t be the expectation for 2011.
“Field and soil conditions are much different than they were a year ago,” he says. “None of the factors of a year ago – late fall harvest, poor tillage conditions, lots of fresh residue on the surface and much N yet to apply – exist this spring. We did a massive amount of tillage last fall, in some cases perhaps more than was necessary.”
One additional benefit for producers is that it has not been wet for extended periods when soil temperatures were warm since N was applied last fall. Most of the N should still be present, with a good deal of it still in the ammonium form and so not subject to loss.
“Though we can certainly feel good about preparations we’ve been able to make for this spring, we know from history that a good fall doesn’t always mean a good crop the following year,” he cautions. “Soils are starting to dry out nicely in some areas, but we need to be careful not to undo the compaction relief provided by last fall’s tillage by driving on soils before they’re dry enough.”
Waiting until soils are dry enough at depth (not just over the surface) will help minimize compaction effects, as will using controlled traffic, making fewer tillage passes, and lowering tire pressure .
Nafziger encourages producers to follow the same practices they have been using when planting corn following corn this year.
“Our research shows that both corn after corn and corn after soybeans respond similarly to planting date and to plant population, so those should change only as soil conditions and productivity might indicate,” he says. “We’ve never been able to identify hybrids that do consistently better in corn following corn, though corn following corn may tend to experience stress (primarily drought stress) and foliar diseases more often, so that should be factored in. And corn following corn typically needs a little more N – see the N Rate Calculator for current numbers.”
Remember the important things this planting season, Nafziger adds.
“Having good soil conditions where the seed  is placed and good rooting conditions beneath the surface are critically important for corn no matter what the previous crop,” he says. “And the crop needs to be well provided with nutrients and protected from pests. Once we cover these basics, the crop will respond mostly to weather factors – water and temperature –that we don’t control. That has always been true, and will be true again in 2011.”