30-40 minutes

Indentify the anatomical features of seeds.
Describe the effects of rough handling on seed.

Seeds have often been called "plants packaged for shipment". If we follow this thinking, then each seed should be stamped with the warning - "Fragile, Handle with Care".  Although all seeds are living things and can be damaged by excessive or improper handling, some are much more fagile than others.  Soybeans, field beans, and other large seeded legumes are especially vulnerable to rough treatment.  These seeds are particularly delicate because of their seed anatomy (see picture).  The seed coat, or testa, of these seeds is very thin and easily cracked.  In addition, the plumule and radicle, parts of the seed embryo, are just under the seed coat and can easily be bruised by rough handling.  Because they are dicotyledons, these plants can easily be broken in two.

Injury to seed from mechanical abuse, harvest, processing, and handling can seriously affect the germination, establishment, and ultimately yield of the subsequent crop.  A 10% reduction in germination can oocur by simply throwing a bag of soybean onto a concrete floor.  Damage is greater when seeds are excessively dry (below 13% moisture).

Special care is taken when harvesting and processing soybeans and field beans used for seed.  The seed is never allowed to fall more than a foot anywhere in the cleaning, packaging, and storage operations.  The elevators and buckets used to transport the seeds are covered in rubber and plastics to dampen seed impact against otherwise hard steel surfaces.  Once the seed has been sold it is up to the farmer or gardener to make sure that the seeds are treated with care.

The following is a demonstration of the hypochlorite soak test used to determine if soybean seed coats have been cracked due to excessive handling. The test is primarily used during harvest to help reduce mechanical damage due to combining and seed handling.   Samples are tested in the field and the appropriate adjustments are made to reduce damage to less than 10% damaged seeds.  The test is also useful in determining processes which cause damage within a seed conditioning plant.

• Soybean seeds (or other large-seeded legumes like fieldbeans or greenbeans)
• Freezer bags (quart size)
• Laboratory beakers - (1 - 1000 ml and 2 - 250 ml)
• Household bleach
• Plastic pan or paper towels
  

1. Weigh out two, 40-50 g samples of soybean seed.
2. Place one of the samples in a freezer bag and drop the bag on a hard surface 10-15 times to damage the seeds.  Rough treatment will be required for the demonstration to work best.  About 5% of the seeds should be broken in half when you are finished.
3. Mix a 1% sodium hypochlorite solution in a 1000 ml beaker using household bleach and water.  Household bleach contains about 5% sodium hypochlorite so you can mix 1 part bleach with 4 parts water to form the 1% solution.  (Handle the bleach using appropriate personal protective equipment and be careful so you don't bleach your clothes.) Hot water, and even coffee, will work in the place of bleach, but may take longer.
4. Place the seed from the freezer bag that you dropped on a hard surface in a 250 ml beaker containing 1% sodium hypochlorite solution.  Place the sample of undamaged soybean seeds in another 250 ml beaker of 1% sodium hypochlorite solution.
5. Allow the beans to soak for a few minutes and then observe the cracked seeds in each lot.  The seed coat of the cracked soybeans will be swollen and separated from the cotyledons.
6. Check again in 15 minutes and record the percent of cracked seed coats.  To make the observation of the seeds easier, strain the sodium hypochlorite from the beaker, rinse the seeds several times with water to get rid of any residual bleach, and gently spread the seed out in a single layer in a plastic pan or on a paper towel.

 
After a few minutes of soaking in the sodium hypochlorite, the seed coats that are cracked will begin to balloon and separate from the rest of the seed and the seed will begin to swell. Seeds can usually be seperated into three different categories follwing a 10 minute soak. Firm - seeds that do not take up solution. These are considered to have little or no damae. Wrinkled - seeds that take up a small amount of solution which causes their seed coats to blister. These seeds are only very slightly damaged. Swollen - seeds that take up solution and appear nearly two to three times their original size. Some may have only a large water blister at one end and others may be breaking apart. These seeds are considered damaged

View a picture of the undamaged seed after soaking

View a picture of the damaged seed after soaking

Bleach is caustic and can cause burning of human tissues, so use it with extreme caution. Appropriate personal protective equipment should be used including eye protection and rubber gloves.

If you are in the Midwest or Southeastern United States, you can obtain soybean from a  local grain merchandiser.  Another option would be to use field bean (kidney, navy, great northern, etc.) purchased at a local grocery store or food market.