SOYBEAN RESPONSE TO FLOODING
When soybean fields are flooded, oxygen available for respiration is limited. Flooding has a negative impact on symbiotic nitrogen fixation (which requires oxygen) and mycorrhizal colonization of soybean roots. In addition, waterlogging leads to accumulations of compounds that are toxic to plants when in high concentrations.
Soybeans can be very resilient. The length of time the crop is subjected to flooding is typically proportionate to crop injury. They may easily survive 48 hours underwater and have been known to survive submersion for a week under ideal conditions during and after flooding. Four days or more of flooding stresses the crop, delays the plants' growth, and causes the plants to be shorter with fewer nodes. Flooding for six days may depress yields significantly, and longer periods under water may destroy the entire stand.
Flooding usually increases soil-borne diseases. Soybeans are always at risk to soil-borne pathogens, but with warm temperatures and favorable seedbed conditions, can often outpace disease infections. However, cool, wet conditions during flooding favor disease development while slowing soybean growth, if growth is stalled for two to three weeks or more.