Stored grain needs to be cool and dry during summer storage, 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 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 about 70 to 90 degrees F. Reducing grain temperatures below 70 degrees will lessen insect reproduction and activity, and temperatures below 60 will reduce insect activity greatly.
Here are a few tips from Hellevang to keep stored grain cool and dry in summer:
• Good bin roof ventilation key. 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 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 a building's attic. The heated air rises and exits near the peak, drawing in cooler air near the eave. However, this natural ventilation won't happen unless the bin has adequate openings at the eave and peak. Roof exhaust fans controlled by a thermostat also can draw the heated air out of the bin if openings are available to allow air into the area above the grain.
• Know when to use aeration. Hellevang recommends cooling grain in the upper portion of the bin by operating the aeration fan about every three weeks during a cool 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.
Also, 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 very 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. The grain moisture content increase is typically less than 1 percentage point because the grain warms and is no longer cool enough to cause moisture to condense onto the grain. So, choose mornings when the air is cool and dry.
• Unload some grain. Some people unload some of the grain periodically during the summer to remove the warmed grain at the top. The grain unloads in a funnel shape in bins with a center sump, with the grain from the top flowing down to the unloading sump at the bottom of the bin.
Removing peaked grain reduces the potential for grain warming at the top of the bin. A cone-shaped peak has a larger ratio of surface area to grain quantity, which leads to more grain warming than occurs with leveled grain. Meanwhile, because air takes the path of least resistance, the aeration airflow will be near the bin walls, with little airflow through the peak. This makes the peak difficult to cool.
• Verify grain moisture. Verify that the grain moisture content is dry enough for storage at summer temperatures. The recommended long-term storage moisture contents are wheat, 13.5%; corn, 13.5%; soybeans, 11%; and grain sorghum, 13%.
The market moisture content may be higher, but storing warm grain at higher moisture contents may lead to mold growth on the grain.
Make sure the moisture content measured by the meter has been adjusted for grain temperature. Confirm the accuracy of the measurement by warming the grain sample to room temperature in a sealed plastic bag before measuring the moisture content.
• Consider storage time. Grain storage life depends on the grain's moisture content and temperature. The allowable storage time is cumulative, so if half of the life is used since harvest, only half remains for the rest of the storage period. This is particularly crucial for grain being stored into late summer or for more than a year.
Each 10 degrees the grain temperature increases reduces the allowable storage time by about half. For example, the allowable storage time for 15% moisture corn is only about 70 days at 80 degrees. The allowable storage time increases to 125 days at 70 degrees and 240 days at 60. This emphasizes the importance of keeping the grain as cool as possible during the summer.
The allowable storage time typically increases by 50% to 75% for each percentage point reduction in grain moisture content, depending on grain moisture and temperature. For example, the approximate storage life of 15% moisture corn at 70 degrees is 125 days. Storage life increases to about 200 days at 14% moisture.
However, that is only about 4.7 months, so if corn is stored at 14% moisture and 80 degrees during the summer, little storage time remains. So, it's important to control grain moisture content and temperature.
This report comes from UNL CropWatch and was originally published as a North Dakota State University news release.