NEWS for North Dakotans
Agriculture Communication, North Dakota State University
7 Morrill Hall, Fargo, ND 58105-5665

September 24, 1998

Ag Engineer Offers Early Harvest Cautions for Corn Drying

Corn harvest is starting earlier than normal this year. That earlier harvest is accompanied by higher temperatures, which can be a benefit and a problem when it comes to drying corn, says a North Dakota State University agricultural engineer.

"Natural air drying occurs more rapidly with warmer temperatures," notes Ken Hellevang of the NDSU Extension Service, "But mold can grow faster and grain can deteriorate more rapidly in warm temperatures as well."

Hellevang notes that warmer air holds more moisture, which increases the speed of natural air drying. Each 5-degree reduction in temperature reduces the water-holding capacity of air by about 20 percent. Therefore, natural air drying should work better in October than in November.

The equilibrium moisture content, the final corn-moisture content when drying with a natural air drying system, will be lower at higher temperatures, Hellevang notes. For example, with a constant relative humidity of 65 percent, the equilibrium moisture content will be about 14.4 percent at 55 F and 15.4 percent at 40 F.

A key to long-term storage of corn is to limit the amount of mold growth and the rate of grain deterioration, Hellevang says. Unfortunately, that becomes more difficult as temperatures rise. The allowable storage time for 20-percent-moisture-content corn is about 42 days at 55 F, 63 days at 50 F, and 95 days at 45 F.

Increasing the moisture content by two percent reduces the allowable storage time by about onehalf. For example, the allowable storage time for 22-percent-moisture corn at 55 F is only about 25 days. Drying corn at moisture contents exceeding about 21 percent is discouraged unless very high airflow rates are used in bins only partially filled.

Natural air drying corn is discouraged until the outside average temperature does not exceed about 50 F, Hellevang says. "At higher temperatures it is difficult to dry the corn before deterioration occurs. It may be advisable to run fans only at night during extremely warm days to keep the corn cooler," he adds.

With an average October temperature of 47 F and 65 percent relative humidity, it will take about 45 days to dry 21-percent moisture corn using an airflow rate of 1 cubic foot per minute per bushel (cfm/bu). Increasing the airflow rate to 1.25 cfm/bu, reduces the drying time to about 36 days. Airflow rates exceeding 1.25 cfm/bu are discouraged for full bins because fan power requirements become excessive.

"If you are drying corn with a natural air system, monitor corn more frequently to assure that the corn will be dried before deterioration occurs," Hellevang says.

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Source: Ken Hellevang (701) 231-7243

Editor: Tom Jirik (701) 231-9629

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