Learn how recent rains have affected Midwestern corn, soybean and wheat crops.
By Susan Jongeneel, University of Illinois
Last week, the remnants of Hurricane Isaac dropped several inches of rain in several parts of the Midwest.
University of Illinois crop sciences professor Emerson Nafziger said that, "While the rain came too late to help corn yields and did little to help soybean yields, it fell very nicely over 3 days. Most of it disappeared without a trace, with creeks still dry, and no tile flow for the moment. Moistened surface soil is the only sign that there has been rain."
In the driest parts of the state, the recent rainfall has helped to restore soil water to more normal levels. At the U of I South Farms, depending on rotation, soil moisture in the top 40 inches is now close to the levels found in late May. Corn following corn appears to have taken in more water, possibly due to larger, deeper cracks. This return to favorable soil moisture lessens concerns about the drought carrying over to next year, though as happened in 2012, rainfall during the season will still be the critical factor.
According to the latest NASS report, as of Sept. 2, 63% of the corn crop was "mature" and 12% harvested while 41% of the soybean crop was listed as "turning yellow" and 7% as "dropping leaves." These numbers will continue to rise in the coming weeks, and both crops have nearly finished adding yield, with corn a little ahead of soybeans.
Growing degree day (GDD) accumulations since May 1, when planting was nearly complete, range from approximately 2,700 in northern Illinois to 3,000 in the southern part of the state. GDD requirements for hybrids grown in Illinois range from approximately 2,500 for very early hybrids to 2,800 for late-maturing hybrids. Thus, GDDs in nearly every field have been sufficient to mature the corn. Most producers are waiting for the corn to dry before harvesting.
The drought caused some cornfields to die, but those that still have some green should be close to maturity (black layer). Nafziger said that, as corn-grain moisture approaches 20%, the advantages to getting the crop harvested tend to outweigh the disadvantages.
"Crop-insurance considerations have to be taken into account, but low-cost drying offered by some elevators, weak stalks that may fall in the next moderate wind, grain quality that can get worse as the crop stands in the field, and the increase in harvest loss as grain dries below 18 to 20% moisture, all weigh on the side of early harvest," he explained.
Reasons for delaying the harvest include the fact that elevator shrink (typically 1.4% per point of moisture loss) exceeds actual shrink (about 1.2% per point), meaning fewer bushels are sold than are actually harvested. This loss, about 1% at 20% moisture, diminishes as grain dries. Last, with soils near field capacity and hence highly compactible in areas where there has been recent rain, it may pay to wait for soils to dry a little before driving a heavy combine on them.