Effects of flooding and saturated soils on corn
Recent and forecasted rain events across the Midwest will lead to many fields with saturated and flooded soils. Areas of these fields that are not flooded with standing water may still remain saturated for an extended period of time.
Survival of corn plants is dependent on temperature, stage of growth and length of time the soil is saturated.
Corn Survival in Saturated Soils
There is no way to tell for sure whether a corn field will survive until enough time has passed to assess recovery of affected plants. The following are some factors that can increase the risk of damage or death.
1. Completely submerged corn is at higher risk than partially submerged corn. Partially submerged plants may continue to photosynthesize at limited rates, extending the amount of time they can survive.
2. Extended saturation will increase the risk of injury and death. Soil oxygen is depleted within about 48 hours of soil saturation. Without oxygen, nutrient and water uptake is impaired and root growth is reduced. A general belief is that young corn plants can survive up to 4 days of ponding if temperatures are in the mid-60s or cooler. With warmer temperatures the plants will use the available oxygen faster and likely will not be able to survive as long.
3. Corn younger than V6 is more susceptible to damage from flooding and saturated soils. The plant’s growing point is still below ground. Once water has subsided the health of the growing point can be assessed by splitting the stalk of an affected plant. A healthy growing point will be firm and white or yellow in color. A damaged or dead growing point will be soft and grey or brown in color.
4. Surface crusts could form if water subsides and the soil dries quickly. This will obstruct air exchange into the root zone, making full recovery less likely.
5. Extended periods of saturated soils will negatively affect the overall vigor of the plant. Root health and growth will be affected until the soil dries to normal levels. Poor root development will leave the corn plant more vulnerable to environmental factors later in the season.
6. Wet soil conditions will promote the development of seedling blight diseases, especially Pythium. The highest risk of these diseases will be in poorly drained areas of the field. The risk will also be higher for corn replanted into these areas. Diseases such as common smut and crazy top also become a much higher risk when corn seedlings are exposed to flooding.
A secondary consequence of flooded or saturated soils is the loss of nitrogen (N). Most water-damaged fields lack the usual dark green color associated with a normal corn crop. Roots’ inability to take up N due to lack of oxygen will cause plants to appear stunted and lack good coloring. This poor color is not necessarily from lack of N in the soil. However, significant N can be lost under these conditions through denitrification (change of fertilizer N to N2 gas under anaerobic conditions) and leaching of nitrate with water percolation into the soil profile.