One of the most important climatic factors influencing soybean growth and development is water. Soybean requiressignificant amount of water during the growing season. Too much or too little water causes stress in plants and ultimately impacts yield. Too much water or waterlogged conditions reduce plant oxygen availability which directly affects respiration and other physiological mechanisms. Soybeans that are in early reproductive stages of pod and seed development (R1 to R5) are more prone to flood stress than later developmental stages. Linkemer et al. (1998) reported that R1, R3, and R5 are the most sensitive reproductive stages of soybean to waterlogging.
Severity of flood damage is dependent on factors such as soil type and temperature. Higher temperatures generally accelerate plant respiration which will deplete oxygen levels faster causing plants to rot. Therefore, plants will have higher recovery and survival chances in cloudy and cooler days following heavy precipitation. Another negative effect of flood in soybean plants is poor nodulation. Soybean roots contain nodules that fix atmospheric nitrogen for the plants to utilize. Waterlogged conditions reduce nodulation sometimes resulting in yellow, stunted plants. One important factor that influences the severity of flood is soil type. Soil type indirectly affects the drainage and duration of waterlogging conditions in any given area. Floods in clay soil can have more detrimental effects on soybean yield than silt loam or sandy soils that have better drainage.
Late season flood followed by warm conditions can create conducive environments for certain fungal diseases. Scouting for diseases like sudden death syndrome and white mold a few weeks after flooding will help develop appropriate management plans. Indirect effects of late season flood is pod shattering. Plants that dried down following flood during the late seed development will have higher chance of pod shattering. After the area is dried up harvesting plants from the in-season flooded area first would help reduce the yield loss from shattering.
Source: David Karki, South Dakota State University