Seed And Seedling Survival In Flooded Conditions

Why flooding affects seeds and seedlings
Seeds and seedlings, regardless of crop type, are living organisms that need oxygen to survive. If seeds or seedlings are deprived of oxygen for about 48 hours, their chances of survival are limited.
If there is still oxygen in the soil and early flooding does not kill plants outright, flooding can still have long‑term negative impacts on crop performance. Excess moisture during early crop stages reduces early root development. Reduced root development limits the plant’s ability to access subsoil water later in the season if summer conditions become hot or dry.
Assessing survival after flooding
After floodwater recedes, plant survival can be assessed:
  • Examine the growing point of the seedling, if present.
  • The stem germinating from the seed (the radicle and coleoptile) should appear white or cream‑coloured.
  • If no germination has occurred, cut the seed in half to check for turgor pressure.
    • If the seed is extremely soft and does not hold its form, it likely will not survive.
Surviving plants typically resume growth within three to five days after the water recedes.
 
Crop response to flooding: crop type, growth stage and duration
Factors that influence flood injury
Crop sensitivity and injury depend on:
  • Crop species
  • Plant development stage
  • Duration of flooding
  • Air and soil temperatures
If temperatures are cool during flooding, survival may be better because plants grow more slowly and require less oxygen. However, cool and wet conditions increase the risk of disease development, particularly from pathogens that thrive under these conditions.
To reduce excess water and disease risk, drainage within one to two days increases the chances of plant survival.
Flood tolerance by crop type
Most annual crops can tolerate:
  • 24 to 48 hours in waterlogged conditions, and
  • Up to 7 days under some circumstances.
In general:
  • Grasses are more tolerant than legumes.
Relative crop tolerance
  • Cereal crops: oats > wheat > barley
  • Pulse crops: fababeans > soybeans >>> field beans > peas
  • Oilseed crops: canola > sunflower > flax
 
Management after flooding
Assessing the crop stand
Before deciding to replant, carefully assess crop damage:
  • Look for rotted seed or damped‑off seedlings, which indicate probable crop losses.
  • Evaluate plant population and stand uniformity.
  • Weigh the potential yield of the remaining stand against the potential yield of a replanted crop at this later date.
Nutrient and weed management
  • An additional nitrogen application may be required in fields showing yellowing or uneven growth.
    • A late nitrate test can help determine whether more nitrogen is needed.
  • Maintain a strong weed control program so surviving crop plants are not robbed of nutrients and moisture later in the season.