June 22-23, some areas of Ohio received a significant amount of rain with some areas receiving as much as 4 to 5 inches.
When plants are completely underwater for approximately 24-48 hours under high temperatures (>80°F), 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.
Under wet conditions, soybeans may turn yellow and also be somewhat stunted. This is often indicative 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 (i.e., converting nitrogen to a usable form), split the nodule with your fingernail and examine the inside. If the inside of the nodule is pink or red, nitrogen is being fixed.
References:
Henshaw, T.L., R.A. Gilbert, J.M.S. Scholberg, and T.R. Sinclair. 2007. Soya bean (Glycine max L. Merr.) Genotype response to early-season flooding: I. root and nodule development. J. Agronomy & Crop Science 193:177-188.