As outdoor temperatures warm, potential increases for grain storage problems, North Dakota State University Extension agricultural engineer Ken Hellevang says. “The stored grain temperature increases in parts of a bin in the spring 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 spring as it does during the summer. That, in addition to the solar heat gain on a bin roof, can create an environment conducive to grain spoilage. A 10 F temperature increase reduces the allowable storage time of grain by about half. The storage time of corn at 17 per cent moisture, for one example, is reduced from about 130 days at 50 F (10 C) to about 75 days at 60 F (16 C) and 45 days at 70 F (21 C).
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Hellevang recommends periodically running aeration fans during the spring to keep grain below 40 F (4 C) as long as possible during spring and early summer if the grain is dry. In northern states, night air temperatures are normally near or below 40 F in May.
Bin vents can become blocked with frost and ice when the fan is operated at temperatures near or below freezing, which may damage the roof. Leave the fill and access door open as a pressure relief valve when operating the fan at temperatures near or below freezing.
Cover the fan when it is not operating to prevent warm air from blowing into the bin or being drawn into the bin due to a chimney effect and heating the stored grain to temperatures more prone to spoilage and insect infestations. Hellevang 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 so the top of the bin can ventilate due to warm air rising — similar to what occurs in an attic — or use a roof exhaust fan.
Hellevang advises stored grain should be monitored closely to detect problems early. Grain temperature should be checked every two weeks during the spring and summer. A temperature increase may indicate a storage problem. 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 the moisture content measured by a meter has been adjusted for grain temperature. Also, 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.
Some in-bin cables estimate grain moisture content by measuring the temperature and air relative humidity and then calculating the grain moisture content based on grain equilibrium moisture content equations. The measured moisture may be one to 1.5 per cent different than the true moisture content, so it is a tool that should be verified with another moisture content measurement method.
Corn needs to be dried to 13-14 per cent moisture for summer storage to prevent spoilage. Soybeans should be dried to 11-12 per cent, wheat to 13 per cent and barley to 12 per cent. The allowable storage time for 13 per cent moisture soybeans is less than 100 days at 70 F.
