With many occurrences of heavy rainfall across Indiana this summer, the question that always gets asked is: “What impacts will flooding and saturated soils have on corn growth and yield?” And the answer to this question is: “It depends.”

Flooding injury to corn is determined by multiple factors. What growth stage was the corn plant at when the flooding occurred? How significant was the flooding and where on the plant did the water rise? How long did the flooding occur? What were the air and soil temperatures at the time of the flooding? How much mud or debris is on the corn plants once the water has drained?

Check growing point

Corn that is younger than V6 is more susceptible to flooding than corn that is older than V6. The growing point of corn at V6 or younger is at or below the soil surface. Therefore, corn plants at this stage are more likely to be completely submerged, thus causing significant damage to the growing point and causing plant death rather quickly.

Within about 48 hours, the oxygen supply in flooded soil is depleted, and the growing point can no longer respire and perform critical functions. If temperatures are warmer than 77 degrees F, corn plants fully submerged above the growing point may not survive after one to three days.

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To confirm plant survival, wait at least three days after the water is drained from the field and check for new leaf growth and the health of the growing point. This can be assessed by splitting the stalk. Healthy growing points will be white or cream-colored, whereas dead growing points will be dark and soft.

Other flooding harms

Corn root growth and function also can be significantly harmed following flooding, especially after soil oxygen has been depleted. The longer an area of a field is flooded, the higher the risk of yield loss and plant death, even if the plants aren’t completely submerged and continue to photosynthesize.

Without oxygen in the soil, corn plants cannot perform critical functions such as nutrient and water uptake, and root growth inhibition and even death will occur. Root system damage to pollinating corn plants could potentially increase photosynthetic stress during the pollination period and grain fill, due to reduced root function.

Flooding also can cause soil and mud to be deposited on corn leaves and within the whorl. This can potentially harm recovering plants and limit overall photosynthesis by hindering the plants’ ability to capture sunlight. It may also damage the waxy surface layer of the leaf.

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In addition, soil and mud deposited on leaves and stalks and within the whorl can encourage the development of fungal and bacterial diseases in the damaged plant tissue. Furthermore, if floodwater rises above the developing corn ear, ear rots can occur.

Lastly, flooding and ponding can cause nitrogen losses from either leaching or denitrification. Fertilizer in nitrate form is negatively charged and can move through the soil profile and below the corn root zone following significant rainfalls. This is most likely to occur on coarse-textured or sandier soil types. In much heavier soils, or low-lying areas of fields where ponding occurs, nitrogen loss most likely occurs due to denitrification.