Question: My corn looked good but turned yellow around the v4 stage due to excess rain. It is starting to turn around and look better with improved weather. How much yield potential have I lost?
Answer:Just how much yield you can expect to lose is hard to say without seeing the crop in the field. When corn is in the 4-5 leaf stage with this kind of water, my experience has been that its survival and quality of survival will depend on your current air-soil temperatures. If the temperatures are in the 45- to 60-degree range, the corn could actually survive being under water for about three days. If the temperature is in the 65- to 80-degree range, however, the plant respiration is so high that after 24 hours there would be a lot of damage. The other problem you have is that any time water goes over the top of corn there will be soil that gets down into the whorl of the corn. The soil that gets into the whorl contributes to crazy top in the corn, so even if it survives there’ll be a percentage of that corn that will be negatively impacted.
I’m also including a news release (see below) that was put out by North Dakota State University Extension recently on this topic. It may give you some additional food-for-thought to help you determine what to expect from your corn crop this season.
Impact of Excessive Rainfall on Corn Growth & Development
Excessive rainfall this spring, following an unusually wet winter, has resulted in extensive flooding in many regions of North Dakota. Even soils that are not visibly flooded quickly become saturated after a rain because there is little evapotranspiration occurring as a result of the low temperatures and lack of an established crop.
Waterlogging (flooded/ponded/saturated soils) affects a number of biological and chemical processes in plants and soils that can affect crop growth in the short and long term.
"The primary cause of waterlogging in crop plants is oxygen deprivation or anoxia because excess water does not react chemically with the plant," says Joel Ransom, North Dakota State University Extension Service agronomist. "Plants need oxygen for cell division, growth, and the uptake and transportation of nutrients. Since oxygen diffuses through undisturbed water much more slowly than well-drained soil, oxygen requirements rapidly exceed that which is available when soils are saturated."
The rate of oxygen depletion in saturated soil is affected by the temperature and rate of biological activity in the soil. Faster oxygen depletion occurs when temperatures are higher and when soils are actively metabolizing organic matter.
Cooler weather will delay the adverse effects of waterlogging on emerged crops. Generally, the oxygen level in a saturated soil reaches the point that is harmful to plant growth after about 48-96 hours. In an effort to survive, tissues growing under reduced oxygen levels use alternative metabolic pathways that produce byproducts. Some of the byproducts are toxic at elevated levels.
"Germinating seeds or emerging seedlings are very sensitive to waterlogging because their level of metabolism is high," Ransom says. "Crops, such as small grains and corn, tend to be more sensitive to waterlogging when their growing point is below the surface of the soil (before the five to six leaf stage)."
With the exception of winter wheat, all of the small-grain and corn crops in the state still are in these sensitive stages (if planted at all) and can be killed if soils are saturated beyond 48 hours and the soil temperature exceeds 65° F.
Crops can differ in their tolerance to waterlogging. Data from differing sources suggest a possible ranking of waterlogging tolerance. The most tolerant to most susceptible are rice, soybeans, oats, wheat, corn, barley, canola, peas, dry beans and lentils. Growth stage and variety can affect this ranking.
"Waterlogged conditions also reduce root growth and can predispose the plant to root rots, so the ultimate effect of excess moisture may not be known until late in the season," Ransom says. "It is common to observe plants that have experienced waterlogging to be especially sensitive to hot temperatures and to display nitrogen (N) and phosphorus deficiencies later in the season due to restricted root development. Yield losses can occur even if these obvious visible symptoms are not observed."
Waterlogging can impact cereal plant growth indirectly by affecting the availability of N in the soil. Excessive water can leach nitrate N beyond the rooting zone of the developing plant, particularly in well-drained, lighter-textured soils.
In heavier soils, nitrate N can be lost through denitrification. The amount of loss depends on the amount of nitrate in the soil, soil temperature and the length of time the soil is saturated.
"Research conducted in other states found losses from denitrification between 1% and 5% for each day that the soil remains saturated," Ransom says.