On-farm storage of soybeans requires some special considerations compared to corn.
As with all grains, spoilage and reduced germination will occur quickly if storage moisture is too high. The high oil content of soybeans makes them even more susceptible to spoilage than corn; therefore soybeans need to be about two points dryer than corn for proper storage.
For winter storage, store commercial soybeans at 13% moisture or less. Soybeans with less than 15% moisture can be dried with bin fans. Soybean seed stored over one planting season should be 12% moisture or less. Store carryover seed at 10% moisture or less.
A portable moisture tester can be used for checking moisture content. Pay attention to the tester’s temperature compensation method because grain temperature can have a large effect on moisture readings. Cold grain generally cause low readings unless moisture has condensed on the surface. All moisture testers show some variability - different readings are obtained when the same sample is tested more than once. To limit this effect, test each sample at least three times and average the readings. Since elevator moisture testers are inspected twice a year by the Iowa Department of Agriculture, you can use them to check your tester’s accuracy. See Using Farm Moisture Testers for more details on how to obtain an accurate moisture reading.
In a normal year, natural unheated air will dry soybeans to 13% moisture. But in cool, wet falls, supplemental heat may be required.
On farms that produce both corn and soybeans, it may be possible to use the same high-temperature drying equipment for both crops. Be careful when drying soybeans, however. They are fragile and can be damaged by air that is too hot or too dry, as well as by rough handling. Soybeans have about 25% less airflow resistance than shelled corn, so fans sized for corn drying will produce greater airflow through soybeans. Greater airflow means faster drying. Reduce heat for soybeans and limit air drying temperature to 130°-140° F. for commercial beans and 100°-110°F. for seed beans. Retention time in the heat section of dryers should be less than 30 minutes.
To avoid differences in moisture levels from top to bottom in batch-in-bin dryers, use shallow batch depths of 2 to 3 feet. With seed beans, set airflow to 6-9 cfm/bu.
Low temperature drying
Low-temperature dryers should have a full perforated floor and a fan that can push an airflow of one to two cfm/bu up through the grain. To avoid overdrying and cracking of soybeans, size heaters on low-temperature bins for no more than 20ºF temperature rise and use an in-plenum humidistat to shut off the heater when the relative humidity of the drying air is below 45%.
Drying time depends on air flow, weather, and initial moisture content but will probably be 3-6 weeks. Check the soybean moisture and condition every day. Resume drying in the spring if necessary. If you detect mold, heating, or foul odors during drying, unload the bin and sell, or dry the beans at high temperatures.
Check all stored grain weekly so you can identify problems before they become unmanageable. Even grain in good condition in the fall can develop problems over the winter.
When checking moisture of binned grain, use a 6- or 10-foot probe to collect samples from various depths (go as deep as possible) at bin center and several other locations. Do not mix the samples. Knowing the moisture content at different locations can help you find the drying front in drying bins or the trouble spots in storage bins. If you don't have a probe, at least take some samples at arms length below the surface.
Other soybean storage tips:
•Level off your bins immediately after harvest.
• Avoid using worn augers and mechanical spreaders that will damage the seed while filling.
•Aerate your bin as soon as it is filled to remove the heat, regardless of the moisture.
•Aerate the stored soybeans to maintain grain temperature at 35° to 40°F in winter and 40° to 60°F in summer.
• Check your bin every couple of weeks throughout the season for sings of crusting, aerate if needed.
• Be sure your bin is ready for unloading before winter. Keep a level seedbed.
For printable PDF bulletins on soybean storage, see these Iowa State University Extension Publications:
Soybean Drying and Storage (Pm-1636)
Have You Checked Your Grain Bin? (SP-46)
Using Farm Moisture Testers (Pm-1633)