Early-Season Flooding and Soybean Survival
Rainfall Sunday night totaled more than 5 inches in parts of south central and eastern Nebraska. Soils became saturated, resulting in flooding and ponding. Other areas of Nebraska's corn growing area need rain.
According to the National Agricultural Statistics Service (NASS) Nebraska Crops Progress and Condition Report, 77% of the state's corn had been planted as of May 11, with 18% having emerged.
Table 1 provides ideas on how long corn can survive. Smaller seedlings are more susceptible than larger seedlings. The effect of standing water on germinating seeds is not well known. Some hybrids will probably respond better than others, yet differentiating among poor and good hybrids is not possible due to limited data. A germinating seed is a living organism and as such requires oxygen to survive. In flooded soil conditions, the oxygen supply will become depleted within approximately 48 hours. Cool air temperatures help to increase the possibility of survival. Yet, we would not expect survival of germinating seeds to be greater than that of young plants; they should not be expected to survive more than four days.
|Table 1. Survival of flooded corn plants. (Adapted from UNL CropWatch, May 20, 2005)|
|Stage||Condition||Potential for Survival and Problems|
|Corn||Germinating||Genetic differences among inbreds (and we assume hybrids) exist for responses to flooding. Will survive for four days. Longer flooding results in lower yields especially at lower nitrogen levels.|
|Corn prior to 6th leaf stage||Underwater (6 inches of water on surface); air temperature less than 77°F||Will survive for four days. Longer flooding results in lower yields especially at lower nitrogen levels. Corn growing points are below the soil surface until V6.|
|Corn prior to 6th leaf stage||Underwater (6 inches of water on surface); air temperature greater than 77°F||May not survive more than 24 hours|
|Corn prior to 6th leaf stage||Saturated, cold soils, flooding||Seed rots, seedling blights, various other pathogens, crazy top|
Additional points on heavy rains, flooding, and crusting. (From CropWatch, May 23, 2011)
- The longer an area remains ponded, the higher the risk of plant death.
- Completely submerged corn is at higher risk than corn that is partially submerged. Plants that are only partially submerged may continue to photosynthesize, albeit at limited rates.
- Corn will survive longer when temperatures are relatively cool — mid-60s or cooler — than when it's warm — mid-70s or warmer. Cooler temperatures forecast for this week will encourage survival.
- Even if surface water subsides quickly, the likelihood of dense surface crusts forming as the soil dries increases the risk of emergence failure for recently planted crops.
- Extended periods of saturated soils after the surface water subsides will take their toll on the overall vigor of the crop.
- Associated with the direct stress of saturated soils on a corn crop, flooding and ponding can cause significant losses of soil nitrogen due to denitrification and leaching of nitrate N. (See earlier CW article.)
- In addition, diseases and other problems can develop due to silt in the whorls.
After the waters recede, confirm plant survival by examining the color of the growing point of the seedlings if present. The radicle (root) and coleoptile (shoot) should appear white or cream colored. Seeds could be cut in half to determine if turgor pressure is still present. If the seed is extremely soft and does not hold form, it probably will not survive. Surviving plants will resume growth within three to five days after the water recedes.
A decision to replant should be made only after assessing stands and considering the economics of replanting or converting the acreage to soybean or another crop. See last week's CropWatch article for replant guidelines. For example, corn planted prior to May 15-25 may yield about 87% of corn that was already planted at 35,000 plants per acre if diseases and insects do not affect the replanted seed or seedling. On the other hand, a stand of 20,000 plants per acre planted before May 15 that survived flooding could yield about 85% of corn planted the same time that has 35,000 plants per acre. Replanting in this example may be hard to justify.
If stands are extremely poor, consider replanting; be aware though that conditions can quickly change with several good days of weather.
- How Corn Plants Respond to Flooding (UNL CropWatch May 24, 2011)
- Corn Survival in Flooded or Saturated Fields (Iowa State University Agronomy Extension)
- After the Rains, Where is the Nitrogen? (UNL CropWatch, May 24, 2011)
- Corn and Soybean Survival in Waterlogged Soils (South Dakota State University iGrow, May 30, 2013)
Extension Cropping Systems Agronomist