Effects of Flooding on Corn
May 30, 2011 by Kevin Gale, CCA
Abundant rainfall totals have accumulated in the past 24-36 hours across many areas of Illinois. With rainfall totals of 3 to 5+ inches in a short amount of time, water is standing or running across many fields this morning. The following article addresses what we should expect with seedling survival and yield potential in these flooded areas.
The effects of flooding on corn are determined by stage of growth, duration of flooding, and air/soil temperatures. Flooding reduces oxygen content within the soil. Research indicates that the oxygen level in soil approaches zero after 24-48 hours of flooding especially where water stands. Without oxygen, the plant cannot perform critical functions such as nutrient and water uptake. It is important to note that flooding may have a long-term impact on crop performance even if the plant is not killed.
Corn injury should be limited if the length of ponding is less than 48 hours. Seedlings may survive as many as four days in cool conditions. Once the water recedes, confirm plant survival by checking to see if the growing point is white / cream color. If the growing point is dark or soft, death is likely. New leaf growth should occur within 3 to 5 days after water drains from the field. Corn whorls filled with soil may prevent the emergence of new leaves. Receiving a light shower once the water gets away may be beneficial to wash off leaves and aid in greater photosynthesis levels. Seed rot and seedling blight (pythium) risk increases in wet, saturated soil conditions. Seed treatments provide good protection for two to three weeks after planting. Early to Mid April planted corn may be more susceptible to seedling blight this year due to the length of time it has sat in the ground, especially in low lying areas. Seedlings may also become infected with the fungus that causes crazy top and common smut, however predicting damage from these diseases is difficult since symptoms do not occur until tassel time. Root growth is often compromised or stunted which may reduce yields should we experience a dry summer.
Nitrogen loss could be a concern due to the abundance of rainfall and saturated soils. According to estimates of denitrification rates from the University of Nebraska, when soil temperature is 55 to 60°F, N loss is 10 percent when soil is saturated for 5 days and 25 percent when saturated for 10 days. Loss accelerates with warmer soils. Research conducted in Illinois indicates approximately 4 to 5 percent loss of nitrate-N present per day that soils are saturated. Many fields have exhibited N loss over the last few years due to excessive rainfall. In those fields where growers were able to add additional N, a yield response was noticed a high percentage of the time.
Deciding whether losses of N are substantial enough to warrant supplemental N includes consideration of several factors:
- Amount of nitrate present when wet conditions occur, which is affected by time of N application, form of N applied, rate applied, and use of a nitrification inhibitor.
- What stage of corn development and the length of time soils are saturated.
- Soil potential for leaching (sandy soils).
- Loss of yield potential from water damage.
- Water movement into soil, leaching, and denitrification are not uniform across the landscape; thus, the potential for N loss is variable.
When considering applying additional N, a Pre-Sidedress Nitrate test can be used. N supplies are adequate if nitrate concentrations are greater than 20 ppm. About 8 lb N/acre should be applied for each ppm of nitrate below 20 ppm. After considering the factors listed above, fields that fit this description may benefit from an additional application of 30-50 lbs of Nitrogen. In many cases, running a toolbar down the rows will help reduce crusting and allow additional oxygen in, improving root growth and overall plant development in addition to supplying additional nitrogen.