Adjust for Soybean Seed Quality with Management

Mike Rankin
Crops and Soils Agent
University of Wisconsin - Extension

Is it true that soybean seed quality will be lower this year?

Most seed companies are reporting that stocks of soybean seed will be somewhat lower than what producers have been accustomed to in previous years.  Hot, dry conditions in late-summer and early fall during 2000 caused much of the soybean seed crop to be harvested drier than normal.  Because the embryo of the soybean seed is located close to the outer seed coat, dry seed predisposes the embryo to mechanical damage during the harvesting and handling processes.  As a result, warm germination of many seed lots in 2001 will be 85 percent or less.  A warm germination test as reported on a seed tag gives an indication of what to expect under "idea" conditions.  Actual germination in the field may possibly be less if soils are cool and wet or hot and dry.

What management practices can be followed to insure a good soybean stand?

     Seeding rates will need to be adjusted upward to obtain the same final stand density if germination percentage is significantly lower than previous years.  How much of an adjustment needs to be made will vary with variety, seed lot, and planting conditions.  Let's take a look at an example.  If a stand density of 200,000 plants per acre is desired, you need to plant about 222,000 seeds per acre if the germination percent is 90 (200,000 divided by 0.9).  Conversely, reaching the same stand density with 80 percent germination seed requires a seeding rate of 250,000 (200,000 divided by 0.8).

     Remember that germination percentages are low because seed was dry and predisposed to mechanical injury.  The seed is still dry and will continue to be vulnerable.  Handle seed as gently as possible this spring.  This means no long "drops" into bins, wagons, or drills.  For bulk soybean seed, the industry suggests using belt conveyers whenever possible.  Brush augers are a good second choice while metal augers need to be avoided.  A poor handling system may drop germination percentages another 10 percent or more.

     Finally, if conditions are less than ideal for planting this spring, growers may want to consider using a fungicide seed treatment.  With lower quality seed, the payback for using seed treatments should be higher than normal.    

What about soybean seed size?

     According to industry spokespersons, soybean seed size will generally be smaller this year.  Again, how much smaller depends on variety and seed lot.  Because seed size has no agronomic significance from the standpoint of seedling vigor or yield potential, smaller seed may be a blessing in 2001.  At least some of the additional seed needed to compensate for lower germination percentage can be recaptured if planting drills are adjusted to plant smaller seed.  The number of seeds per pound for each seed lot is listed on the seed tag.