In terms of crop concerns, there are numerous things to worry about with the current floods and saturated soil conditions around Ohio. In corn, aside from the physical damage of flood waters, there can also be costly nitrogen loss.
“There is no tool or test that can tell how much has been lost. An estimate can made on the loss potential, which is based on N source, time of application, soil temperature, and number of days that soils have remained saturated,” wrote Ed Lentz and Steve Culman with Ohio State University Extension in a recent CORN Newsletter. “Most nitrogen that is lost from a field is in the nitrate form during wet conditions. Time of transformation to nitrate is dependent on the type of N fertilizer applied. Anhydrous ammonia is less susceptible to loss since it converts to nitrate rather slowly. Urea-ammonium nitrate (UAN) solution has about 25% as nitrate at application time has a greater risk for loss than anhydrous.
“Soils have been warm enough that some transformation to nitrate may have already occurred this year depending on application date. However, the nitrate N will not be lost by denitrification unless soils have remained saturated long enough. Risk of loss is minimal for soils that remain saturated for one day, moderate risk for two days of saturation, and a substantial risk for three or more days of saturated conditions. Standing water is evidence of saturated soils, but even soils without standing water are considered saturated if an individual cannot walk across without making footprints.”
Here are some factors to consider when evaluating the potential for N loss that were developed by the University of Minnesota and modified to Ohio conditions by OSU Extension. The system asks a series of questions and assigns a point value depending upon the answer. Higher point totals indicate a higher probability of a response to addition N.
Factor 1: What N product was used?
Anhydrous ammonia with N-Serv: 2 points
Anhydrous Ammonia: 3 points
Other fertilizer banded: 4 points
Other fertilizer broadcasted: 5 points
Factor 2: When was the majority of the fertilizer N applied?
After April 20: 3 points
Before April 20: 5 points
Factor 3: What has been the field soil moisture status the past month?
Normal soil conditions: 1 point
Wet soils: 3 points
Standing water/saturated soils: 4 points
Factor 4: What is the crop’s current condition?
Green plants > 12 inches tall: 1 point
Green plants < 12 inches tall: 2 points
Chlorotic plants < 12 inches tall: 3 points
Chlorotic plants > 12 inches tall: 5 points
Total the score for the four factors and use the following guidelines:
Less than 11: No supplemental N recommended
11‑16: Evaluate again in 4-7 days
17 or more: Add an additional 40 or more pounds of N per acre
For soybeans, there are several potential problems in ponded saturated conditions. Laura Lindsey and Anne Dorrance, with OSU Extension, compiled a list of potential issues to consider in saturated soybean fields.
1. Flooding: In fields that have had standing water for more than 48 hours, you’ll notice stunted soybeans and a smell as you approach the “drowned” out areas. When you dig the roots up, they may or may not be brown but the trick is that the outer layer of the root tissue, the cortical cells, can be easily pulled off leaving the white center of the root or root stele. The roots almost look like rat tails.
When plants are completely underwater for approximately 24 to 48 hours under high temperatures (warmer than 80 degrees), they will likely die. Plants respire more under high temperatures, oxygen is depleted, and carbon dioxide builds up suffocating the plant. Cool, cloudy days and cool, clear nights increase the survival of a flooded soybean crop. If the waters recede quickly and the plants receive some light rain, they can recover.
2. Poor nodulation: Yellow, stunted soybeans are symptoms of poor nodulation. Nodules are the small knots found on roots, often near the top of the root system. Nodules are the result of a symbiotic relationship between soybean and bacteria (Bradyrhizobium japonicum). These bacteria convert nitrogen into a form that is usable by the soybean plant.
Nodulation is reduced in wet soils. Soybeans at the V2 growth stage when grown in saturated soil for two weeks retain the ability to recuperate nodule function when normal (aerobic) conditions are restored. To determine if a nodule is actively fixing nitrogen split the nodule with your fingernail and examine the inside. If the inside of the nodule is pink or red, nitrogen is being fixed.
3. Disease: Flooded and saturated soil conditions will also provide the optimum conditions for the water molds that are common across the state. In these cases, the whole roots are brown, sometimes with dark brown lesions on the roots, and the tissue can be brown to tan. Both Phytophthora sojae and Pythium are contributing to this problem. Once the soybeans are at the V2 growth stage or greater, the protection from the seed treatment is gone and we are relying on the soybean plants’ defense system to mitigate the damage. For these areas in Ohio, the Rps genes for Phytophthora will only protect a few of the plants; we are relying on the partial resistance (field resistance, tolerance) part of the package.
What can you do? Wait. When dryer weather returns the roots will re-establish. The roots just need some oxygen to get moving again. Check your drainage, these are excellent opportunities to see where some improvements can be made.