Considerations for flooded corn and soybean
To determine whether supplemental N should be applied in corn, consider the In season corn N calculator.
This worksheet is more accurate when corn is at the V5 or V6 stage rather than when it is smaller. For entire fields or portions of fields meeting the requirements for supplemental N, this worksheet recommends a rate of 40 to 70 lb N/ac, depending on the situation. However, with the high cost of N fertilizer, producers planning to apply supplemental N based on this worksheet need to have a have a clear idea about how much N they should apply. Research conducted by Dr. Gyles Randall, retired University of Minnesota soil scientist, showed that supplemental N applied at 30 to 40 lb N/ac is sufficient for corn following soybean on most soils or corn following corn on medium-textured soils such as silt loams. In contrast, higher rates, possibly up to 60 to 70 lb N/ac may be needed on heavy (finer-textured) soils where corn follows corn and high amounts of surface residue are present. Additional information on N management during this difficult growing season can be found in a recent Minnesota Crop News, The Annual Nitrogen Newsletter.
Agronomic considerations for soybean
Although soybean is generally sensitive to excess water, soybeans can survive underwater for a week or more under ideal conditions. Generally, soybeans tolerate 48 hours under water quite well, but flooding for 4 to 6 days can reduce stands, vigor, and eventually yield. Many factors determine how well a soybean crop will tolerate flooding. The most important factors that determine the fate of flooded soybean fields are: 1) duration of the flooding, 2) temperature during the flood, 3) rate of drying after the flooding event, and 4) growth stage of the crop during the flood. Yield losses are seldom noted in fields flooded for 48 hours or less. Four days or more of flooding stresses the crop, delays the plants' growth, and causes the plants be shorter with fewer nodes. Flooding for 6 days or more can depress yields significantly, while flooding for a week or more may result in significant (or entire) losses of stand.
Temperature during the flooding event plays a large role in determining the fate of a submerged soybean field. Higher temperatures cause the soybean plant to more quickly deplete its stored energy. Additionally, soybean plants appear to be very sensitive to high carbon dioxide (CO2) levels in the soil. Higher temperatures cause plants and soil microbes to respire at high rates that quickly deplete the water of oxygen and increase CO2 levels. Cool, cloudy days and cool clear nights greatly increase the survivability of a submerged soybean crop.
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