What corn farmers should know about flooded fields

 

Weekend rains caused flooding in many farm fields, including this one in Luverne, Minnesota.

Heavy rains soaked much of Minnesota this weekend and left parts of many corn fields under water.

“It doesn’t sound like there are too many whole fields flooded, but there’s definitely flooded out low spots and saturated fields,” said Dave Nocolai, a University of Minnesota Extension Crops Educator.

Southwest Minnesota up into the Willmar area appears to have been hit the hardest. However areas of Northwestern and East Central Minnesota which already had wet soil and planting conditions received additional precipitation.

When flooding or ponding occurs in corn fields, it takes some time to accurately assess the damaged plants. Young corn can survive flooded conditions lasting for about two days under warm temperatures (at or above mid-70ºF) to four days under cooler temperatures (at or below mid-60ºF) according to Dr. Jeff Coulter, University of Minnesota Corn Extension Specialist.

Survivability also is influenced by how much of the plant was submerged and how quickly the water recedes. Corn plants that survived flooded conditions should show new leaf development 3-5 days after water recedes. Flooding and saturated conditions also restrict root development, thereby reducing the crop’s ability to take up water and nutrients and tolerate drought stress later in the season.

With prolonged ponding or saturation in corn fields, nitrogen (N) loss can occur through leaching and denitrification. Denitrification occurs under oxygen-depleted conditions that result when all of the soil pore space is filled with water. Under these conditions, soil microbes utilize nitrate for respiration, and N is released as a bi-product in gaseous forms that are lost to the atmosphere. To determining whether supplemental N should be applied in corn, consider the in-season corn N calculator worksheet developed by the University of Minnesota.

In general, corn should not be planted for grain after mid-June in Minnesota. According to the research summarized in the corn replant guide, expected yield of corn planted on June 19 is 59 percent of maximum. Further, corn planted in mid-June or later is at high risk of being froze in the fall prior to maturity, even if an early-maturity hybrid is selected.

However, corn planted for silage can generally be planted as late as June 25 in southern Minnesota, if hybrids are selected that are 15 or more relative maturity units earlier than full-season for the region.  For more information on re-planting, consult the University of Minnesota Extension corn replant guide.

If you’re a corn farmer with questions about flooded or ponded areas of your fields, the University of Minnesota Extension’s crop-e-news “Considerations for Flooded Corn and Soybeans” is an excellent resource.

Farmers should also be in touch with their area soil conservationist about erosion issues caused by excessive rains.

Purdue University also has a helpful information sheet on flooding.

A special thanks to Dave Nicolai and Dr. Jeff Coulter at University of Minnesota Extension for assisting with much of the information in this blog post.

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