Soybeans can be harvested as long as the moisture is 20% or less. Threshing is more difficult and soybeans are more susceptible to damage when moisture is 18% or higher. Moisture testers can underestimate the moisture content of immature or high moisture soybeans, to compensate, consider adding 1.5% to moisture tester readings. Wet soybeans will need to be aerated immediately after harvest.
Spoilage during storage is a concern when moisture levels are high. High oil content makes soybeans slightly more susceptible to spoilage than corn, so soybeans need to be about 2 points dryer than corn for the same storage period (Table 1).
Low-temperature drying. Low-temperature dryers should have a perforated floor and a fan that can provide 1 –2 cubic feet/minute of airflow. Drying time depends on air flow, weather, and initial moisture content but will probably be at least 6 to 8 weeks in the Upper Midwest during the late fall. Therefore, heat may be needed to lower the relative humidity. Prolonged exposure to air drier than 40 percent relative humidity may result in excessive soybean cracking. Over drying and cracking of can be reduced by not allowing more than 20° F temperature rise and use an humidistat to shut off the heater when relative humidity of the drying air is below 45 percent. Check soybean moisture and condition every day or two. Run the fan continuously until the drying front reaches the top layer of beans or average outdoor temperatures fall below freezing. Resume drying in spring if necessary. If you detect mold, heating, or foul odors during drying, unload the bin and sell or high-temperature dry the beans.
High-temperature drying. Soybeans are fragile and can be damaged by air that is too hot (over 140° F), as well as by rough handling. While it is possible to use the same high-temperature drying equipment for both corn and soybean, heat should be reduced for soybean. Air drying temperature should be 130° F to 140° F for commercial soybeans and 100° F to 110° F for soybean seed. Be sure to monitor for split beans during drying and adjust temperatures accordingly.
Tips for High Temperature Drying
- Limit drying air temperature to 130°-140° F with a retention time of no more than 30 minutes.
- Avoid excessive moisture differentials from top to bottom in batch-in-bin dryers, by using shallow batch depths (two to three feet) when drying soybeans.
- Soybean dry quickly so check moisture frequently and if a bin stir is available, only stir once to avoid grain injury.