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Should Carry-Over Soybean Seed Be Used this Spring?

There were a record number of unseeded acres last year. This means not all soybean seed intended for the 2019 growing season was used. Can carry-over seed (grown in 2018) be used successfully in 2020?  Before answering that question, it must be stated that soybeans are one of the least storable seeds when compared to many other crops. This is largely because of their high oil content. The length of time a seed lot remains viable is influenced by the initial seed quality, seed moisture, relative humidity, and temperature. Studies have shown that higher temperature and relative humidity during storage will increase the rate of deterioration. Maximum seed quality is reached at physiological maturity and begins to decline after that point. Seed deterioration is impossible to stop and cannot be reversed. Only the rate of deterioration can be slowed by controlling the storage environment. One study showed that seed viability remained high (>92%) over a 20-month period in cold storage (10˚ C) but declined in warm storage (25˚ C) to 78%. The seed stored in a warehouse with fluctuations in temperature and relative humidity dropped to almost 0% over the same 20-month period (Gladys Mbofung et al. 2013 “Effects of Storage Temperature and Relative Humidity on Viability and Vigor of Treated Soybean Seeds”, Crop Science, Vol. 53, May-June.). Therefore, it’s not considered good practice to keep soybean seed from one year to the next, unless it has been stored in a controlled environment and tested.
If carry-over seed is to be used this spring a germination (warm test) and vigour (cold) test should be conducted to determine the viability of the seed. Results from 67 seed lots tested in Michigan this spring showed a significant decline in the viability of the carry-over seed compared to new seed.
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