Correspondent
MADISON
With a significant portion of Wisconsin’s soybean crop still awaiting harvest at the start of November, growers might become anxious to get their beans off the field and into storage when they still have a moisture content that’s considerably above the 13 percent that is ideal for safe storage.
In a recent advisory, the University of Wisconsin Extension Service Team Grains noted that soybeans can be harvested with little or no damage at up to 18 percent moisture but warned that “artificial drying is necessary” if the moisture content is “much above 13 percent.” They also commented that it is “not a good situation when growers need to consider artificial drying of soybeans.”
The grains team of agriculture agents Bill Halfman, Greg Andrews and Bob Cropp explained that artificial drying presents several challenges “in order to keep the soybeans at an acceptable quality level to avoid dockage.” They also pointed out that there isn’t much published research on drying soybeans and that most of the current drying recommendations are drawn from the far more common experience of drying corn.
On that point. Team Grains turned to University of Minnesota crop storage and handling specialist Bill Wilke for guidance. He provides recommendations for natural air, low temperature and high temperature methods to dry soybeans.
Wilke notes that natural dry drying of soybeans usually takes two to six weeks and should be attempted only in bins with fully perforated floors and with fairly large drying fans that deliver 1 to 1.5 cubic feet of air per minute per bushel – respective horsepower of 0.6 to 1.6 per 1,000 bushels – for an 18 foot depth of soybeans. He indicates that managing natural air soybean dryers is similar to that for natural air corn dryers except for having to get the moisture content 2 percentage points lower than for corn.
For southern Wisconsin, Wilke calculates that the needed airflows would be 1 cubic foot per minute per bushel for soybeans put into bins at 17 to 18 percent moisture, 0.75 cubic foot at 15 to 17 percent moisture and 0.5 at 13 to 15 percent moisture. For central and northern Wisconsin, he would bump the respective airflow numbers to 1.5, 1.25 and 1 cubic feet for the three moisture categories of the soybeans under natural air drying.
A small amount of supplemental heat is an option with natural air drying to cope with cool and damp weather such as that which has been persistent into early November of this year but don’t overdo it, Wilke advises. “Do not heat the beans more than 3 to 5 degrees Fahrenheit or you will over dry the beans and could cause an increase in splitting. Exposing soybeans to a relative humidity of less than 40 percent can cause excessive splitting.”
Alternatives to supplemental heating for natural air drying are turning off the fans when the temperature drops before freezing and turning them back on when the day’s average temperature is above freezing, installing bigger fans to complete the drying before winter sets in and turning off the fan during times of high humidity, Wilke indicates. Shutting off the fan during high humidity will obviously delay the drying but will ultimately result in drier beans, he promises.
A third, but tricky option for drying, is a high temperature, typically natural gas-fired, dryer, Wilke points out. “But be careful and refer to the manufacturer’s recommendations for maximum drying temperature.”
For nonfood soybeans, some bean and skin cracking can be expected at the recommended maximum of 130 degrees while the maximum would be 110 degrees for soybeans being saved for seed in order to avoid killing the embryo, Wilke notes. Anyone choosing the high temperature approach should be prepared for “trial and error,” examine beans leaving the dryer for splits and realize that grains dried in gas-fired dryers must be cooled within about one day to remove the dryer heat, he adds.
To soybean growers whose plants were killed by frost before the seeds were fully mature, Wilke stresses the importance of removing “as much chaff and green plant material as possible before binning the beans.” He explains that immature beans can be stored without a significant likelihood of molding in many cases but warns that green chaff can stimulate heating while in storage.
With green soybeans, make sure they are clean when going into storage, evenly distributed in the bin and cooled as soon as possible after harvest, Wilke concludes. “It might be worthwhile to store green soybeans for a few months to avoid the high price discounts that would apply if large quantities of green beans are delivered during harvest.”
