ain began to fall on July 4 and continued for a week
with at least nine weather reporting sites showing 10 or more inches for the
week. Most of the heavy rains fell in the northern one-half of the state.
The net result of all of this rain is saturated soils in the northern one-half of the state with significant ponding and severe flooding along most streams. Anytime these types of wetness problems occur, the immediate question relates to the length of time that a given crop can survive if covered by water. For soybeans, the length of time that a plant can remain completely submerged and survive is between 2 and 4 days assuming the soils were not saturated when the flooding occurred. The length of time is also related to temperature and cloud cover. Hot, sunny conditions may result in death of the plant after 2 days or less while, with cool, cloudy conditions, soybeans may survive after 4 days or more. If a portion of the plant is exposed above the water, soybeans have been known to survive after 7 days of partial submersion. If flooding occurs in fields where the soils have already been saturated for a few days, the soybean plants are less likely to survive. Once the flood water recedes, the leaves will remain covered with soil or making them very inefficient.
Soybeans require well-aerated soils to grow vigorously. Saturated soils, with no water on the above ground portion of the plant, can result in poor root and plant growth and some plant death from root rot diseases. After only a few days of saturated soils (anerobic), soybean plants become a lighter green color due in part to poor nitrogen fixation. The rhizobium, responsible for nitrogen fixation, will die under these water logged conditions and the nodules will become soft and will decay. As soon as the soil dries adequately to become aerobic, new root growth will occur and nodule formation will resume. During the last week, we have had a number of cloudy days that have also contributed to the poor growth and light green or yellow color of the soybeans.
The bottom line is that growing conditions are far from ideal for the soybean crop. Warm nighttime temperatures, bright sunny days and a few days free of added rainfall will bring this crop around and change its appearance significantly. These changes need to occur shortly since the soybean plant has moved into the reproductive stages of growth and continued stresses can begin to take a toll on yield potential.