How Saturated Soils Affect Corn and Soybean Growth

Categories: GROWING, CORN, SOYBEANS
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​​​​​​​​​​​​​​Excess rainfall can cause saturated or "water-logged" soils that can negatively affect crop growth and yield. Water-logged soils can impact oxygen availability, crop survival, nitrogen levels and soil pH. We’ll dig into these issues a bit more, then share several management practices to help your corn and soybean crops recover from saturated soils.

Oxygen Availability
Soil oxygen is essential for germination, root respiration and nutrient uptake. Flooded or saturated soils can reduce the amount of oxygen available for developing crops and have a direct impact on plant growth.

Crop Survival 
Temperature and crop growth stage influence how long corn and soybeans can survive in saturated soils. In warm conditions, the crop grows faster and uses available oxygen more rapidly, so much that it can cut the chances of surviving extended saturation in half. Cooler conditions lead to slower crop growth, which can give the crop an extra day or two before depleting oxygen. 

Corn younger than the 6-leaf stage can typically survive up to 4 days in saturated conditions. After the 6-leaf stage, the odds of survival increase slightly because the growing point is above the soil surface. As corn moves into reproductive stages (pre-tassel to silking), excess water is less likely to impact plant survival unless submerged for several days. However, standing water can lead to poor pollination and nutrient deficiencies critical for grain fill, which can severely impact yield potential.

Soybeans can survive a flooding up to about 8 days at the V2 to V3 vegetative stages, but keep in mind nodulation/nitrogen fixation can be reduced, causing chlorosis and stunting. Meanwhile, 2 to 3 days of water-logged conditions during the soybean reproductive stages usually causes greater yield reductions than the vegetative stages. Water-logged soils at R1 can reduce the number of pods per node, and reduce seed size at R5, both leading to yield reductions. Also note some soybean varieties tolerate water-logged soils better than other varieties.

Chances of survival for both crops is traditionally very good when water drains from flooded fields within 2 to 3 days. If weather conditions are favorable and damage to plants isn’t severe, new leaf growth should be visible within 3 to 5 days.

Soil Nitrogen and pH 
Excessive rain and wet soils can cause loss of lower nitrogen levels through leaching and denitrification. Leaching occurs when nitrates move beneath the root zone and typically happens in well-drained soils. Denitrification occurs when nitrates are reduced to a gaseous form and lost into the atmosphere. This is more common in poorly drained soils. 

In some situations, soil pH can become more acidic because of water-logged soils. While this condition may be temporary, lower pH in the root zone can affect the availability of certain nutrients.

Management Practices
The following management practices help improve soil aeration and structure to promote plant growth after fields have been flooded.
  • Once soils are dry enough, cultivation during the early- to mid-vegetative stages helps open and aerate the surface layer to promote root growth.
  • Cornfields that are yellowing and growing unevenly may benefit from additional nitrogen. Before applying, consider the field’s yield potential and make sure the hybrid can reach its full maturity. Apply additional nitrogen prior to lay-by to achieve the most yield benefit.

Nitrogen Side Dressing Tips
  • A late spring test for soil nitrates when corn is 6 to 12” tall can help assess how much nitrogen is available to the plant just before the rapid growth phase begins. Decisions about additional nitrogen needs can then be made.
  • If no soil test is available and deficiency symptoms appear, a general rule of thumb is to apply 40 to 50 units of nitrogen. Rain or irrigation shortly after application helps move nitrogen to the root zone for nutrient uptake.
It may go without saying, but the best way for crops to recover from saturated soils is warmer, sunnier weather that dries out the surface and root zone layer to promote plant growth and overcome environmental stressors. Weather conditions in the mid to upper 80os with periodic, but moderate rainfall, are perfect conditions to see in your forecast.

Contact your Golden Harvest Seed Advisor with questions or for additional agronomic insights.

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