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Drying Soybean in Late October
The moisture holding capacity of air is directly related to the air temperature. The moisture holding capacity of air at 50F is twice that of the air at 30F. Therefore, it will take twice as long to dry at 30F as it would at 50F. Drying in the field or in the bin will be much slower at cooler temperatures.
Freezing grain does not result in drying. Typically when temperatures are freezing at night, the air is dry during the day. For example at 100% relative humidity at 25F will only have a relative humidity of about 38% when heated to 50F. This low humidity level with a nice breeze dries grain well. This higher humidity level along with the cool air temperatures, results in very slow drying.
Harvested grain can be stored during the fall and winter at fairly high moisture contents if it is kept cool using aeration. The allowable storage time doubles for each 10 degrees that the grain is cooled. Corn at 22% moisture can be stored for 190 days at 30 degrees, but only 60 days at 40 degrees. Aeration fans should be operated to cool the grain to near freezing as quickly as possible. The grain can be cooled later to 20-25F for winter storage.
The equilibrium moisture content for soybeans is about 13.2 to 14% when the relative humidity is about 70% and air temperature ranges from 50 to 30F. Therefore, drying should be occurring in the field, but will be slow due to the cold temperatures. Soybeans can be natural air dried in a bin with adequate airflow. The recommended airflow rate is at least 1.0 cfm/bu for 16%, 1.25 for 17% and 1.5 cfm/bu for 18% soybeans. The expected drying time is three to four weeks, but will be longer at cooler temperatures. Adding enough supplemental heat to warm the air by 5 degrees will dry the beans to about 11% moisture, but will only increase the speed of drying very little. Adding more heat will cause the soybeans to be dried to a lower moisture content. The temperature of a high temperature column drier should be limited, because the number of cracked beans increases at warmer temperatures. The number of cracked beans in one study was 5-20% at a dryer air temperature of 100F at 20-70% at 130F.
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