The effects of recent Midwest flooding of corn fields has only slightly negatively impacted crop ratings in the last week, but there are some corn fields that have died during a time when they are typically able to withstand high moisture.
Emerson Nafziger, University of Illinois crops specialist, says that while he normally expects corn in mid- to late vegetative stages to be able to withstand a week or so of flooding, the corn that stood in water in mid-June suffered greater and faster decline than he expected.
There are several reasons why corn crops at this stage die so quickly after growing well into June.
"Plants that look like they dried up actually did," Nafziger says. "Roots without oxygen can do very little, including taking up water for more than a few days. The high temperatures at that time meant high demand for water, which hastened the demise.
"Finally, the warm water standing in the low spots carried little dissolved oxygen, so the roots failed quickly."
Nafziger says it's likely that roots of plants that did not stand in water also suffered some damage from saturated soils, even if soils were very wet for only a day or two.
"The soil compaction that we have had since last fall, and that we added to this spring, likely restricted roots to an unknown extent, but probably less than did lack of oxygen," he says. "As a result, we expect that the root system of the crop is shallower, less extensive and less active than we would like.
"This is at a time when the plant needs all of the resources like sugars that it can muster to complete vegetative growth and begin the pollination process. This lack of additional sugars will reduce the amount of new root growth."
During this recovery process, Nafziger says growers need to let the crop tell them how it's doing. If it regains and maintains upright, fresh-looking leaves, this means that it's taking up water well; if its leaf color deepens, then the plant is taking up the nitrogen it needs.
"Such processes obviously need good roots, so we'll be anxious to see if the plant can juggle its needs for roots, tassels, silks and the last additions of top growth, all with a more or less fixed supply of photosynthesis and the sugars it produces," he says.
Nafziger says the high temperatures that dropped into the upper 70s and lower 80s this past week will greatly assist corn in its recovery from excessive wetness and what may be less-than-ideal root systems. Low night temperatures reduce the loss of sugars to respiration, and lower daytime temperatures will reduce water loss rates slightly, he says, while bright sunshine means higher rates of photosynthesis, which increases water use.
"As soils continue to dry out, helped greatly by water uptake by roots, roots will be recharged with oxygen and they might grow some more if there is enough sugar to go around," Nafziger says. "Roots usually reach their maximum size at about silking, though, so we can't expect a lot of additional root growth.
"This means that our best hope is that it not stop raining for very long over the next two months."