The storability of grain depends on grain quality, moisture content and temperature. Grain moisture content must decrease as grain temperature increases to store grain safely, says Ken Hellevang, North Dakota State University Extension Service grain drying expert.
The allowable storage time for 22% moisture corn is about 190 days at 30°, 60 days at 40° and only 30 days at 50°. Therefore, as stored grain temperature increases, the grain moisture content must decrease for safe storage. The allowable storage time for 18% moisture corn at 50° is 90 days.
Stored grain temperature increases in the spring due to outdoor temperatures increasing and solar heat gain on the bin. Solar energy produces more than twice as much heat on the south wall of a bin in early spring than during the summer. This causes grain temperature to increase rapidly in the spring.
Immature grain and grain with damage to the seed coat is more prone to storage problems, so the grain should be stored at a lower moisture content than normal, Hellevang says. Also, stored grain should be monitored more closely to detect any storage problems early. Grain temperature and moisture content should be checked every two weeks during the spring and summer. Grain should be examined for insect infestations, as well.
Grain should be kept cool during spring and summer storage. Periodically run aeration fans to keep the grain temperature below 40° during the spring.
When checking the moisture content of stored grain, 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° are not accurate, Hellevang says.
Verify the accuracy of the measurement by warming the grain sample to room temperature in a sealed plastic bag before measuring the moisture content.
Hellevang says another problem is that grain storage molds will grow and grain spoilage will occur in grain bags unless the grain is dry. Grain in the bags will be at average outdoor temperatures, so grain will deteriorate rapidly as outdoor temperatures increase unless it is at recommended summer storage moisture contents.
Corn at moisture contents exceeding 20% should be dried in a high-temperature dryer because of the potential for cornfield molds to continue to grow at moisture contents exceeding about 20% when grain temperature increases above about 40°.
For natural air drying, ensure that the airflow rate supplied by the fan is at least 1 cu. ft./minute/bushel (cfm/bu) and the initial corn moisture does not exceed 20%. Start drying when the outside air temperature averages about 40°. Below that temperature, the moisture-holding capacity of the air is so small that very little drying occurs.
An airflow rate of at least 1 cfm/bu is recommended to naturally air dry up to 16% moisture soybeans. The expected drying time with this airflow rate will be about 50 days. The allowable storage time for 18% moisture soybeans is only about 40 days at 50°, so a minimum airflow rate of 1.5 cfm/bu is recommended to naturally air dry 18% moisture soybeans.
For more information, visit NDSU's grain drying, handling and storage Web site.