With harvest well underway, it is always important to ensure proper grain storage, especially as farmers build larger grain bins than in the past. This week, I’ve decided to share an article written by my Extension colleague, Tom Dorn in Lancaster County which was featured on UNL Extension’s CropWatch website, Managing Large Grain Bins for Potential Mycotoxin Contamination. Dorn points out that a typical on-farm grain bin traditionally was 27 to 36 feet in diameter and would hold 18 to 22 feet of grain depth. Now it is common on many farms to build 42- to 48-foot diameter bins that can hold 28 to 32 feet of grain depth.
These large bins work well for storing dry grain and regulating grain temperature. The low airflow rates that are good for controlling grain temperature require relatively low static pressure to move the air through the grain mass. Generally, fans intended for temperature control are sized to produce 0.2 to 0.3 cubic feet of air per minute per bushel (cfm/bu) through the grain. Many fan manufacturers produce a 10 horsepower axial-flow fan capable of producing 0.3 cfm/bu in a 48-foot diameter bin with 30 feet of corn depth.
Using a 48-foot diameter bin for drying corn is a much different situation. The minimum airflow recommended for drying corn in Nebraska is 1.0 cfm/bushel. An even higher airflow is required for grain that has, or even might have storage molds that could continue to grow and produce mycotoxins in storage. The higher airflow will dry the grain more quickly. Drying time is proportional to the airflow, cfm/bu, and the airflow a fan can produce is affected by the grain depth. Therefore, Dorn recommends reducing grain depth to provide higher airflow (1.25 cfm/bu or higher) and shorter drying times.
Remember, while a minimum of 1.25 cfm/bu is recommended, providing more airflow is better. Drying time is inversely proportional to the airflow (cfm/bu). An airflow of 2 cfm/bu will dry corn in half the time as an airflow of 1 cfm/bu.
To achieve the recommended 1.25 cfm/bu in a 48-foot diameter bin using only one 40 hph fan, grain depth would need to be limited to 8 feet or less. If two 40 hp fans are used, grain depth needs to be 15 feet or less to achieve the recommended airflow.
If mycotoxins are suspected in corn, grain depths in large bins may need to be adjusted to facilitate quick drying. For more information on grain bin storage visit the Lancaster County Extension site.