Stored grain in the Northern Plains needs to be kept cool and dry during the spring and summer. Temperatures should below 70 degrees F — about 60 degrees would be even better because insects aren’t very active — and moisture content should be 13.5% for wheat, 12% for barley, 13.5% for corn, 11% for soybeans, 13% for grain sorghum, 8% for oil sunflowers and 10% for confectionary sunflowers. The market moisture content may be higher, but storing warm grain at higher moisture content may lead to mold growth on the grain.
But running aeration fans in the spring and summer to keep stored grain cool and dry is tricky. Aeration can warm the grain and increase moisture levels if the fans are operated at the wrong time.
Ken Hellevang, North Dakota State University Extension grain specialist, recommends the following five steps to keep grain cool and dry:
• Cool grain in the upper portion of the bin by operating the aeration fan about every three weeks during cool, dry early mornings. Using positive-pressure aeration to push air up through the grain enables the cool grain in the bottom of the bin to cool the air, which then cools the grain near the top of the bin. Run the fan only long enough to cool the grain near the top surface. Running the fan more than necessary will warm more grain at the bottom of the bin, increasing the potential for storage problems. If the air dew point is warmer than the grain temperature or if the air relative humidity is high, some moisture will condense onto the grain during fan operation. Condensing moisture will release heat that will warm the air slightly, reducing the effectiveness of the aeration and increasing the amount of warming occurring in the grain at the bottom of the bin. Therefore, selecting mornings when the air is cool and dry is important.
• Cover the aeration fans when you are not using them to prevent wind and a natural chimney effect from warming the grain. Wind blowing into uncovered fans or ducts will move air through the grain in a way that is similar to operating an aeration fan.
• Ventilate the space between the grain and the bin roof. Openings near the eave and peak work like the vents in an attic of a building. The heated air rises and exits near the peak, drawing in cooler air near the eave. This natural ventilation will not occur unless the bin has adequate openings at the eave and peak. Roof exhaust fans controlled by a thermostat also can be used to draw the heated air out of the bin if openings are available to allow air into the area above the grain.
• Verify that the grain moisture content is dry enough for storage at summer temperatures. Measure and record the stored grain temperature at several locations near the top surface, along the walls and within the stored grain. “Temperature sensors are an excellent tool when monitoring stored grain, but remember that they only measure the temperature of the grain next to the sensor,” Hellevang says. “Because grain is a good insulator, the grain temperature may be much different just a few feet from the sensor. Increasing grain temperature may be an indicator of an insect infestation or mold growth.”
• Check stored grain every two weeks. Mold growth and insect infestations occur rapidly at summer temperatures. Using insect traps or placing grain samples on white material helps you look for insects. “A situation with only a few insects can turn into a major infestation in less than a month,” he says.