Wilcke says wet harvest conditions resulted in the storage of some wet shelled corn and soybeans last fall. Cold weather generally protected these crops from mold and insects during the winter. "Stored crops that are cooled to less than 30 degrees F during the winter can be stored at fairly high moisture levels with minimal risk of spoilage," he points out. "But during spring and summer we lose the ability to keep crops below 30 degrees F, so we need to reduce moisture content to avoid spoilage."
Wilcke says corn should be dried to 14-15 percent moisture for storage into spring, 14 percent for storage into summer, and 13 percent for longer-term storage. Soybeans should be 12-13 percent moisture for storage into spring, 12 percent for storage into summer and 11 percent for longer-term storage. Stored crops will probably mold if they are wetter than these levels and are aerated only by a small fan delivering less than 0.5 cubic feet of air per minute per bushel of grain in the bin.
Using a gas-fired dryer in late winter or early spring is an option for both corn and soybeans, says Wilcke. After drying, cool the crop to less than 50 degrees F for summer storage. That means drying needs to be completed before average outdoor temperatures rise above 50.
Wilcke says you can expect energy costs for gas-fired drying to be about one to two cents per bushel per percent point of moisture removed. Total drying costs, including labor, depreciation and repairs, will be two to four cents per bushel per point. Labor, equipment and transportation costs for moving crops to the dryer and back to storage will add a few more cents per bushel.
"You can dry soybeans in gas-fired dryers, but the seeds will split if you dry them too fast or the temperature is too high," says Wilcke. "Therefore, it's important to use a much lower drying temperature for soybeans than for corn. If you plan to use any of the soybeans for seed, keep the drying temperature below 110 degrees F to avoid killing the seed embryo."
Natural-air drying may be another option for slightly wet corn and soybeans, says Wilcke. For this you need a bin with a full perforated drying floor and a drying fan that can deliver about one cubic foot per minute per bushel. For further information check a University of Minnesota Extension Service bulletin entitled "Natural-Air Corn Drying in the Upper Midwest," item BU-6577. It's on the Internet at http://www.extension.umn.edu/distribution/cropsystems/DC6577.html.
"Spring drying must be started early," says Wilcke. "If you wait too long and the weather gets too warm, the crop at the top of the bin will mold before it dries. The crop at the bottom of the bin will get drier than it needs to be. The wetter the crop, the earlier you need to start."
For corn wetter than 19 percent moisture, Wilcke says the natural-air drying process needs to begin as soon as average outdoor temperatures stay above freezing. This is usually around mid-March. Turn on the drying fan and let it run until the drying front moves through the top of the bin. For 17-19 percent moisture corn, start drying around April 1, and for 15-17 percent corn, start drying around April 15.
The same dates apply when natural-air drying soybeans, but the moisture levels should be about two percentage points lower. This means you should start drying beans that are wetter than 17 percent moisture at mid-March. For beans that are 14-15 percent moisture, Wilcke suggests controlling the fan, either manually or with a humidistat, so that the fan only runs when relative humidity is less than about 70 percent.
For more information on drying soybeans, check the drying, handling and storage chapter in the University of Minnesota Extension Service "Minnesota Soybean Field Book," item MI-7290. This publication and "Natural-Air Corn Drying in the Upper Midwest" are both available for a nominal fee from county offices of the University of Minnesota Extension Service. Or, call (800) 876-8636 or 612) 624-4900 to purchase the publications.