Minnesota Extension Engineer
Because of wet conditions during harvest last fall, a number of farmers currently have shelled corn or soybeans in their bins that are too wet for safe storage into spring and summer. What moisture levels are safe for storage? Crop storability is a function of both temperature and moisture. The colder the storage temperature, the higher a crop's moisture can be before molds and insects cause quality loss. During winter, if stored crops are cooled to less than 30F, they can be held at fairly high moisture levels with minimal risk of storage. During spring and summer, we lose the ability to keep crops below 30F (unless we choose to spend money on refrigeration) and we need to reduce moisture content to avoid spoilage. Corn should be dried to 14 to 15% moisture for storage into spring, 14% for storage into summer, and 13% for longer-term storage. Soybeans should be 12 to 13% moisture for storage into spring, 12% for storage into summer, and 11% for longer-term storage.
If stored corn or soybeans are wetter than the values just listed, and the storage bin is only equipped with a duct-type aeration system and a small fan that delivers less than 0.5 cfm/bu (cubic feet of air per minute per bushel of grain in the bin), the crop will probably mold this spring or summer. Crops should be sold, fed, or moved out of the bin and dried to a safe moisture level before the weather gets too warm.
Using gas-fired dryers in late winter or early spring is an option for both corn and soybeans. After drying, the crop should be cooled to less than 50F for summer storage, so make sure drying is completed before average outdoor temperatures get above 50F. Expect energy costs for gas fired drying to be about $0.01 to $0.02 per bushel per percent point of moisture removed and total drying costs (energy plus labor, depreciation, repairs, etc.) to be $0.02 to 0.04 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. Soybeans can be dried in gas-fired dryers, but the seeds will split if dried too fast or at too high a temperature, so a much lower drying temperature should be used for soybeans than for corn. If any of the soybeans will be used for seed, drying temperature should be kept under about 110F to avoid killing the seed embryo.
If a bin is available that has a full perforated drying floor and a drying fan that can deliver about 1 cfm/bu, natural-air drying can be another option for slightly wet beans and corn. The University of Minnesota Extension Service bulletin, Natural-Air Corn Drying in the Upper Midwest, BU-6577, gives a good overview of natural-air drying and provides suggestions for spring drying. Spring drying must be started early because if a person waits too long, the weather will get too warm and the crop at the top of the bin will mold before it dries and the crop at the bottom of the bin will get drier than it needs to be. The wetter the crop is, the earlier you need to start. For corn wetter than 19% moisture, start watching the weather in mid-March, and as soon as it stops snowing and average outdoor temperatures stay above freezing, turn on the drying fan and let it run until the drying front moves through the top of the bin. For 17 to 19% moisture corn, start drying around April 1, and for 15 to 17% corn, start drying around April 15.
For natural-air drying of soybeans, use the same dates listed in the previous paragraph for corn, but reduce moisture values by about 2 percentage points. In other words, for soybeans wetter than 17%, start drying in mid-March. For soybeans that are 14 to 15% moisture, it might make sense to control the fan - either manually or by using a humidistat, so that the fan only runs when the relative humidity is less than about 70%.
For more information on soybean drying, see the drying, handling, and storage chapter in the University of Minnesota Extension Service Minnesota Soybean Field Book, MI-7290.