Corn following corn may be getting its second strike this season, says University of Illinois Extension agronomist Emerson Nafziger.

"Despite different planting season and crop conditions in 2011 than in 2010, we are again hearing that corn following corn is producing lower yields than corn following soybean in many areas," Nafziger notes.  "In some cases, I've heard reports of corn following soybean yielding in the range of 230 bushels per acre, while corn following corn in the same area planted with similar practices is yielding in the 160 to 170 range. We don't expect corn following corn to average 60 or 70 bushels less than corn following soybean over whole areas, but this does illustrate what will again be a significant issue in some fields this year."

It was easy to attribute last year's decreased yields in corn following corn to weather. In 2011, he doesn't have as clear a picture about why growers are seeing this problem again.

What happened this year to result in a second year of substantial yield loss in corn following corn? Nafziger offers the following:

The spring of 2011 started out well, with some corn planted in early April. Almost all of this was corn following soybean, given that such fields tend to dry out faster and need less work in the spring. It turned wet and cool after that, and planting stalled at about 10 percent complete through the rest of April. So planting was, on average, late in 2011.

Once the calendar turned to May and it dried up enough for field work, planting got underway in a big rush with about 60% of the crop planted over the first two weeks of May. Many fields planted during this period were wetter than ideal. This not only caused more compaction, "undoing" much of the benefit of tillage last fall, but it also brought issues of residue interference, seed placement, and effects of heavy equipment in many corn-on-corn fields.

As a result of the above, many reported that corn following corn looked bad from the start, with uneven stands, poor color, and other problems associated with planting into such cool, wet conditions. Some who attempted to apply extra nitrogen, foliar nitrogen, micronutrients, or other things to try to "bring the crop around" generally found that these didn't do a lot of good. Starter fertilizer helped some to make stands look more uniform, but did not completely solve the problem.

The heavy rainfall in May and June in some areas was a repeat of what we saw in 2010. But with the crop not nearly as far along in 2011 and with June temperatures not as high as in 2010, immediate effects of this heavy rain on the corn crop were not as severe in 2011 as in 2010. This did delay the return of the crop to normal color and growth in corn following corn.

When the rains stopped in many areas in late June, and soils dried in July and August, the effects were much more severe in most corn-on-corn fields than in fields where corn followed soybean.  Due to drier soils, root systems generally developed better and remained healthier in 2011 than in 2010. But with compaction, slower growth due to less (and a less green) canopy, residue, possible tillage effects, and other factors at work in corn following corn, it seems that the ability of the roots to extract water compromised in corn following corn compared to corn following soybean. Both crops seemed to pollinate okay, but corn following corn showed more leaf stress in July and August, and reduced light interception was evident in many fields where corn followed corn. This increased kernel abortion and decreased the ability of the crop to fill the kernels it had.

In the driest areas, corn following corn lost canopy color and died prematurely, often before corn following soybean. This stopped the filling of kernels, and in many cases, led to more stalk quality problems.

After corn-on-corn has done so well in recent years, many growers are discouraged to have a second year of lower yields in many corn-on-corn fields. Many will find that their profitability will be higher with corn following soybean than corn following corn this year, even accounting for what have often been lower returns from soybeans than from corn in recent years, Nafziger adds.

"We can't simply decide to plant more corn acres following soybean in 2012 than we did in 2011; we planted only about 9 million acres of soybeans in Illinois both years, and acres of corn following soybean the next year can't exceed that number," he says. "So as long as corn acreage stays near the 12 million acres of recent years, some 20% to 25% of Illinois corn will have to be corn following corn."