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Dealing with impact of flooded fields and saturated conditions


ST. PAUL, Minn. (7/10/2018)--Flooding, ponding, and saturated soils continue to impact crops across southwestern and south central Minnesota. Intense rains, ranging from 6 to 8 inches or more in several counties in southwestern Minnesota on July 3, exacerbated the wet conditions.
Partially flooded corn field
Flooded field in southwestern Minnesota, July 3.
Photo by Extension educator Liz Stahl  


Potential damage to crops depends on several factors, including:
  • crop stage during the flooding/ponding 
  • duration of the flooding/ponding 
  • air/soil temperatures, and 
  • rate of drying and soil type 
Crop development stage is quite variable this season due to a wide range of planting dates. Partially submerged plants have a better chance of survival than completely submerged ones, although root development and nutrient uptake will still be impacted.

Corn impacts

Corn at the V5 stage (five leaf collars) can generally survive two to four days of flooding, although plants may not survive more than 24 hours when temperatures are above 77°F. Corn at the V7 to V10 stage can generally tolerate standing water for seven to ten days, depending on the temperature. During pollination, corn is more susceptible to flooding, as this is one of the most critical stages for corn development in determining yield potential. In general, significant yield losses can be anticipated after two to four days of standing water at this growth stage.

Yellow corn, a sign of nitrogen (N) deficiency, can be observed in fields across the region due to excessive moisture and prolonged saturated conditions. N-deficient corn can respond to N applied as late as pollination, but at this point in the season, no more than about 30 pounds of N/ac would be recommended. If N is broadcast on tall corn, urea is the safest N source. Yield potential of the crop and the ability to increase yield with N is likely compromised at this stage in the growing season, so take a hard look at the cost-benefit of the application for your situation. Extension’s supplemental N worksheet for corn, available at https://z.umn.edu/suppN, can help in this decision.

Soybean impacts

Soybean can generally survive being under water for 48 hours. Four days or more of flooding stresses the crop, delays plant growth, and causes the plants be shorter with fewer nodes. Flooding for six days or more can depress yields significantly, while flooding for a week or more may result in significant (or entire) losses of stand.

Dealing with drowned-out spots

Ideally, once the flood waters recede, drowned-out spots should be planted to non-crop covers to suppress weeds while reducing the effects of fallow syndrome. Fallow syndrome can occur if “good” fungi that help in nutrient uptake die off since there are no living roots to survive on. This can impact yield potential of the crop the following year.

Potential cover crop options can be found at: https://z.umn.edu/ccoptions. Be sure to match cover crops with any applied herbicides, and follow rotational restrictions listed on the herbicide label if grazing or feeding of the cover crop is desired. See https://z.umn.edu/ccandherbicides for more information.

A low-cost option for drowned-out spots is soybean, although soybeans planted beyond mid-July may not produce a harvestable crop. Planting soybean into a soybean-on-soybean situation is not preferred. Even very small areas of soybean-on-soybean can lead to reservoirs of soybean pests and diseases that will affect subsequent soybean crops for years to come.

More resources

More detailed information on flooding impacts on crops can be found at: https://z.umn.edu/floodedcrops, and the Extension crops website https://z.umn.edu/crops.

The information above is from the following University of Minnesota Extension crops team members: Liz Stahl, crops educator; Jeff Coulter, corn specialist; Seth Naeve, soybean specialist; Fabian Fernandez, nutrient management specialist.

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Media Contacts: Allison Sandve, Extension news media manager, ajsandve@umn.edu, 612-626-4077 (office) or 651-492-0811 (mobile)

For more news from U of M Extension, visit www.extension.umn.edu/news or contact Extension Communications at extnews@umn.edu. University of Minnesota Extension is an equal opportunity educator and employer.

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