Standing water can be detrimental to crop stands and in turn yields, but the severity of the effect is dependent upon several factors. The growth stage of the crop during flooding, duration of the flood, temperature while the water is standing, and rate of drying after the flood.
If fields are under standing water for 48 hours or less, yields losses are generally minimal or non-existent. Flooding for 4-6 days can delay plant growth, cause the plants to be shorter with fewer nodes and can depress yields significantly. If fields are flooded for a week or more, entire losses of stand can occur.
Low oxygen levels in are detrimental to respiration, a vital function for plant growth. Considering the low levels of oxygen contained in water when compared to air, plants in a flooded field get far less oxygen for needed processes. Depending on water movement, oxygen levels in flooded soils can reach zero within 24 hours. One advantage that we have had during this growing season as it relates to water in the field is the cool temperatures that we have been experiencing in Kentucky. Warm air temperatures increase the speed of respiration and depletes the oxygen from the soil even quicker, leading to rotting and death of the plants. This increased respiration by plants and soil microbes also leads to exponential increases in CO2 levels, which has as great or greater effect than lack of oxygen.
Other effects of waterlogged soils include root diseases, and nutrient deficiencies, including nitrogen, potassium, and manganese.
Image: Potassium deficiency in soybeanReferences: University of Minnesota Extension, Iowa State University Extension
K deficiency image courtesy of Chad Lee, University of Kentucky
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