Water, Water Everywhere: What Happens To Flooded Corn And Soybeans?

Jun 25, 2015
By Angie Peltier
The Northwestern Illinois Agricultural Research & Demonstration Center (NWIARDC) has had 4.73 inches of rain so far in June, 4.4 inches of which fell over a 10 day period. Relatively speaking, the Monmouth area lucked out, as a little bit further to the East Peoria has accumulated 9.06 inches of rain since June 7 and 4 days of more than 1 inch (1 had 2.83 inches total).
Image citation: Daren Mueller, Iowa State University, Bugwood.org
Frequent and significant rain events and saturated soils can remind a crop producer about a lot of things: 1) which fields could stand to be tiled, 2) where grassed waterways need repairing, 3) where grassed waterways might need to be established, 4) that it might be time to get in touch the crop insurance agent.
According to conversation yesterday (June 18) with a representative of one of the companies that offers crop insurance throughout the state, 2015 is so far a typical year - granted, this was before any rain from tropical storm "Bill" mad its way into the state. Through this one company, there have been approximately 1000 re-plant claims, 67 prevent-plant claims (primarily in the South), and about 600 hail damage claims (McClean County and points North). What has been atypical in 2015 is the fact that fields are so wet that claims adjusters have been unable to perform their inspections. Regardless, producers are urged to contact their crop insurance representative within 72 hours of noticing a potential crop claim.
Although most producers in the Monmouth area were able to get their crops planted in a timely manner, there are a now lot of corn and soybeans sitting under water. In many fields it might just be one or two small ponded areas, while fields in the river-bottoms near the Spoon or Illinois Rivers or some creeks may be completely submerged.
What flooded soils do to developing plants. The dangers to roots from flooded soils are many. Flooded soils quickly become devoid of oxygen which is essential for proper root function. We know that plant leaves are able to use the sun's energy to convert CO2 and water to oxygen and glucose through a process known as photosynthesis. Respiration is sort of the opposite of photosynthesis, where oxygen and glucose are converted back into energy (and CO2 and water) that is used to run the machinery of cells. On a typical day there is a balance between respiration and photosynthesis. On sunny days more photosynthesis than respiration occurs, allowing plants to make the building blocks essential for growth and development, eventually contributing to yield.
All of the organisms that live in soil need to respire to live and function. This includes many bacteria, and soil-living fungi, nematodes, insects and plant roots. Flooded soils quickly become oxygen-free (anaerobic) environments that do not support aerobic respiration. In the absence of oxygen, respiration still continues to occur in the soil and in roots, but this anaerobic respiration leads to the build-up of substances toxic to cells (ex. ethanol, organic acids). Additionally, while an anaerobic soil environment certainly does not favor normal cellular functions, root growth or development, prolonged oxygen deprivation can lead to cell death and death of roots or the whole plant.
Corn. According to the Illinois Agronomy Handbook, corn is very vulnerable to damage from flooding when it is younger than the six-leaf (V6) growth stage and the growing point is still below-ground. Only 3 to 4 days of being submerged in floodwater can be fatal to these young plants. Luckily, most of the corn in the region is further along in its development, and plants with above-ground growing points are better able to tolerate a week or more of standing water. If plants survive the flooding, root growth and function can continue to be reduced even after the flood waters recede. If root development is retarded, they may be unable to access the subsoil moisture needed to meet water and nutrient demands of plants in the reproductive growth stages.
Additionally, there can be concerns regarding soil nitrogen retention as flooding can lead to nitrogen loss through denitrification and leaching. Stay tuned for information about a season-long soil nitrogen monitoring that is taking place throughout the state this year. Information is likely to be shared in the Illinois Pest Management and Crop Development Bulletin.
Soybean. Flooding can also be detrimental to soybean root growth function and nodule formation and function.Without proper nitrogen fixation, soybean leaves can begin turning yellow. Research has shown that photosynthesis can be reduced by 1/3rd with 48 hours of flooding (Oosterhuis, 1990). This reduces dry matter accumulation both during and after flooding and can reduce seed yields. One bright spot is that after water drains away, photosynthesis and dry matter accumulation can resume.
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