By Dr. Kenneth Hellevang, North Dakota State University
Stored grain needs to be cool and dry during the summer, a North Dakota State University Extension Service grain-drying expert says.
"Cold or cool grain has been safely stored through the summer for many years," notes Ken Hellevang, an Extension agricultural engineer. "Keeping the grain as cool as possible should be the goal of spring and summer grain storage."
Allowing grain to warm to average outdoor air temperatures during the summer can lead to insect infestations and mold growth. The optimum grain temperature for insect activity is approximately 70 to 90 degrees. Reducing grain temperatures below 70 degrees will lessen insect reproduction and activity, and lowering grain temperatures below 60 degrees will greatly reduce insect activity.
Hellevang warns that using aeration could warm the grain, which may increase the moisture content of the grain slightly. Aeration fans should be covered 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.
One challenge to keeping the grain cool during the summer is that solar energy on the bin roof heats the air above the grain. Convection currents in the grain flow up along the bin wall and down into the grain near the top middle of the bin, drawing this heated air into the grain. Ventilating the space between the grain and the bin roof can reduce the amount that the grain near the top of the bin is warmed.
Natural ventilation to cool this space can occur if the bin has openings near the eave and peak; these openings 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.
Cool grain in the upper portion of the bin by operating the aeration fan about every three weeks during a cool early morning. 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. That may require running the fan for a few hours during a cool, dry morning for a couple of days. 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.
Verify that the grain moisture content is dry enough for storage at summer temperatures. The recommended long-term grain storage moisture contents are about 13.5 percent for wheat, 12 percent for barley, 13.5 percent for corn, 11 percent for soybeans, 8 percent for oil sunflowers and 10 percent for confectionary sunflowers. The market moisture content may be higher, but storing warm grain at higher moisture contents may lead to mold growth on the grain.
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. 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.
Mold growth and insect infestations occur rapidly at summer temperatures, so stored grain should be checked every two weeks. A situation with only a few insects can turn into a major infestation in less than a month. Using insect traps or placing grain samples on white material helps you look for insects.