No. 15/July 3, 1998
Water- and Wind-Damaged Corn
Heavy storms this week have again refilled the low parts of some fields in Illinois, with corn of all ages--early planted, replanted, late planted--standing in water or in saturated soils. Much of the corn that has been in saturated soils from earlier rainfall is showing the yellowing and stunting that is characteristic of a nonfunctioning root system. Theyellowing and slow growth are due most directly to a lack of nitrogen (N) during what should be a period of rapid growth. Although N losses have taken place, and will continue as soils stay wet, most yellowing is probably due to an inability of the plant to take up N, rather than a shortage of N in the soil.
As soils dry out and roots again receive the oxygen they need to function and to grow, green color should return to corn located in wet areas of fields. Unfortunately, this drying out will take some time, and the delay during which the plant does not grow or function well may limit the potential of the corn plants to recover and yield normally. There has not been much research on this, but observations would tend to indicate that plants once stunted and N-deficient during the middle and late stages of vegetative development often do not recover fully in terms of height, weight, or ear and kernel size. This makes sense, in that leaf size and ear size are both being determined during the middle stages (V6 to V12 or so) of vegetative development, and potential kernel number and size are determined by the time tassels appear. The root system is also growing rapidly during vegetative growth, and a slowdown in the overall growth rate due to saturated soils, especially when warm air temperatures already favor top growth at the expense of root growth, will severely slow the growth of roots.
Because the damage due to standing water appears to be mostly N deficiency, producers may be thinking about applying additional N fertilizer in affected parts of the field. Applications to taller corn are usually made by dribbling or spraying UAN solution on the soil surfacebetween the rows. Dribbling can probably be done in alternating rows as well: This will increase the rate in each band, causing more solution to soak into the soil, where it is less prone to loss of the urea N in UAN.
Although it is difficult to predict a response to application where corn has been damaged by standing water, such application should put N closer to the roots that begin to recover their function first as the soils dry. Such N should be taken up by the plant sooner than N deep in the soil, where soils will stay wet longer and roots will take longer to resume growth and function. This difference in time of resumption of N uptake could be critical because developmental events are rapid as the crop approaches tasseling.
Although late vegetative growth is a time of rapid N uptake, the amount of N needed to bring about some recovery of growth in flooded areas is not large. Unless you conclude that all N has been lost, we would probably suggest a supplemental application of only about one-fourth to one-third the amount of N initially applied.
We have received a few reports of "green-snap" caused by winds that accompany storms. This is a phenomenon--thankfully not very common in Illinois--in which stalks break due to high winds, usually during late vegetative development, but sometimes during or soon after pollination. Most of the breakage takes place at a nodal plate about a foot or two abovethe soil surface, meaning below the ear in most cases. Some hybrids may appear to be more susceptible than others, but the main factors that determine what fields are affected are growth stage and speed of growth when the winds occur. Lignin forms to toughen stalks and nodes as they get older, but young nodes can grow only before much lignin forms, so theytend to be weak.
Unfortunately, there isn't much we can do about this sort of stalk breakage. Stalks that break below the ear will produce no grain, of course. Salvage value for forage is not very high, as the broken-off tops are difficult to harvest, and the standing stalks have little dry weight and may contain high nitrate levels. Replanting with soybeans or with some sort of forage crop (including corn) might be the only reasonable recourse.
Where storm winds pushed plants over without breaking stalks, plants should "gooseneck" back up, and providing that they can re-establish the root system that may have broken off, they should have good yield potential. Dry soils or insect damage to the root systems can result in drought stress and slow growth, however, and may limit recovery from such injury.
Emerson Nafziger (email@example.com), Crop Sciences, (217)333-4424