The recent heavy rains have created flooded conditions in many areas of Michigan and producers need to understand how the standing water will affect their soybean fields. There is a lot of information available regarding the effects of flooded or saturated soils on emerged soybeans and this information is summarized in the Michigan State University Extension article, “Assessing water damage to emerged soybeans.”
There is less information about how flooding affects the germination of recently planted soybean seed. A 2001 journal article, “Flooding and temperature effects on soybean germination,” by Wuebker et al. is a commonly cited reference on this topic. The research was conducted in a growth chamber so that temperature, timing of the flooding and the duration of the flooding could be controlled and varied. The researchers looked at two temperatures, 59 and 77 degrees Fahrenheit, three timings, one, two and three days after imbibition (seed swell or 12 hours after planting) and five durations of flooding ranging from 1 hour to 48 hours.
The researchers found that overall, flooding adversely affected germination more severely at 59 F than at 77 F. This was true regardless of the duration of the flooding. They also showed that damage was reduced by warmer soil temperatures when the flooding occurred one to two days after imbibition. At 59 F, flooded conditions lasting for only 1 hour reduced germination rates by 22%.
Timing and duration effects
When seed was flooded one day after imbibition, the duration of the flooding had less effect on germination than when the flooding occurred two to three days after imbibition. Germination was reduced by 33% when flooding occurred after two days and lasted for 48 hours and by 43% when flooding occurred after three days and lasted for 48 hours.
The research proves that flooding adversely affects soybean germination. However, producers should remember that this information was generated in a controlled environment and many factors such as seed quality, soil texture, pathogen population, soil structure and surface and subsurface drainage will affect the soybean germination in your fields. The only sure way to know the extent of the damage, if any, is to assess your soybean stand in the areas where water ponded for several days.