By Ken Hellevang
As outdoor temperatures increase, stored grain requires attention to prevent losses, says Ken Hellevang, North Dakota State University Extension agricultural engineer and grain drying expert.
The stored grain temperature increases in the spring not only due to an increase in outdoor temperatures, but also due to solar heat gain on the bin. Solar energy produces more than twice as much heat gain on the south wall of a bin in early spring as it does during the summer.
Hellevang recommends periodically running aeration fans to keep the grain temperature near or below 30°F until the grain is dried if it exceeds recommended storage moisture contents, and below 40°F as long as possible during spring and early summer if it is dry. Soybean oil quality may be affected in less than four months if even 12% moisture soybeans are stored at 70°F.
Cover the fan when it is not operating to prevent warm air from blowing into the bin and heating the stored grain. He also recommends ventilating the top of the bin to remove the solar heat gain that warms the grain. Provide air inlets near the eaves and exhausts near the peak or use a roof exhaust fan.
Bin vents can become blocked with frost and ice when the fan is operated at temperatures near or below freezing, which may lead to damage to the roof. Leave the fill and access door open as a pressure relief valve when operating the fan at temperatures near or below freezing.
Monitor Grain Moisture, Temperature
Stored grain should be monitored closely to detect any storage problems early, Hellevang advises. Grain temperature should be checked every two weeks during the spring and summer. Grain also should be examined for insect infestations.
Check the moisture content of stored grain to determine if it needs to be dried. Remember to verify that the moisture content measured by the meter has been adjusted for grain temperature.
In addition, remember that moisture measurements of grain at temperatures below about 40°F may not be accurate. Verify the accuracy of the measurement by warming the grain sample to room temperature in a sealed plastic bag before measuring the moisture content.
Corn needs to be dried to 13% to 14% moisture for summer storage to prevent spoilage.
Soybeans should be dried to 11% and wheat to 13%. The allowable storage time for 13% moisture soybeans is less than 100 days at 70 degrees.
Corn at moisture contents exceeding 21% should be dried in a high-temperature dryer because deterioration is rapid at warmer temperatures. For example, the allowable storage time of 22% moisture corn is about 190 days at 30°F, but only 30 days at 50°F.
Recommended Airflow Rates
- Corn. For natural air-drying, assure that the fan's airflow rate is at least 1 cubic foot per minute per bushel (cfm/bu) and the initial corn moisture does not exceed 21%. Start the fan when the outdoor temperature averages about 40°F.
- Soybeans. Use an airflow rate of at least 1 cfm/bu to natural air-dry up to 15% to 16% moisture soybeans. Start the fan when the outdoor temperature averages about 40°F. Follow the manufacturer's recommendation for high-temperature drying soybeans. Monitor the soybean quality and reduce the drying temperature if excessive cracking or splitting occurs. Reduce the fire hazard by keeping the soybeans flowing in the dryer. Pods and trash can become lodged and combustible. Frequently clean the dryer to remove anything that may impede flow. Constantly monitor the dryer when drying soybeans.
- Wheat. Use an airflow rate of at least 0.75 cfm/bu to natural air-dry up to 17% moisture wheat. Start drying when the outside air temperature averages about 50°F.
"Remember that some of the allowable storage life was used during the fall before the grain was cooled to near or below freezing, so there is less time for spring drying before deterioration occurs," Hellevang says.