A Grain Harvest, Drying And Storage Dilemma Back »

This article was written collaboratively by Bob Fanning, , former SDSU Extension Plant Pathology Field Specialist, and Steve Pohl.


Many producers are expecting a fall harvest that will exceed their grain bin capacity, as well as the storage capacity at the local elevator. Planning ahead as to what crops to harvest first, where each crop will be stored, and what to do in the event of crops that require aeration or drying may pay big dividends.

The recommended moisture content for short-term storage (less than 6 months) of clean, sound grains, with aeration available if needed, for the most commonly grown crops are as follows: corn – 15.5%, millet – 10%, grain sorghum – 13.5%, soybeans – 13%, non-oil sunflower – 11%, oil sunflower – 10%. If storing for longer than 6 months, lower moisture contents are recommended. Producers are advised to check stored grain on a regular basis for moisture migration, insect activity, mold development and increase in grain temperature.

With the large crop expected this fall, many producers may want to begin harvest when the earliest crop is above the recommended moisture content and dry it to a safe level. Weather conditions could also make harvesting some of the crop at higher than recommended moisture contents necessary in order to avoid large field losses.

When harvesting grains above the recommended moisture content, the length of time the crop can be stored without excessive dry matter losses is a function of the moisture content and the grain temperature. This is called allowable storage time (AST), and is based on no more than 0.5% dry matter loss from kernels with normal harvest damage. Kernels with greater than normal damage will spoil two to five times faster. At higher moisture levels, AST becomes critical. AST for shelled corn at 20% moisture and 45° F is 67 days, but at 60° F, is only 28 days. A table with estimated AST’s for corn at various moisture contents and grain temperatures is available in the factsheet, Grain Drying Guidelines for a Wet Fall Harvest. AST’s for crops other than corn have not been well established, but can be estimated based on the AST’s for corn by taking into account the difference in recommended moisture contents between corn and the crop that is being stored. For example, the maximum recommended moisture content for corn is 13.5%, 2% higher than sorghum, which is 13.5%, therefore 15.5% moisture sorghum may be closely compared to 17.5% moisture corn, etc.

If grain needs to be stored longer than the AST expected with the moisture content and temperature of the grain, you have two choices, cool the grain with aeration (if possible) or dry the grain. True aeration occurs with an airflow rate of one-tenth cubic foot of air per minute per bushel of grain (0.1 cfm/bu), and will change the temperature of a bin in 100 to 200 hours of fan operation. Higher airflow rates will accomplish the cooling in proportionately less time (0.5 cfm/bu = 20-40 hrs). The grain will only be cooled to near the average outside air temperature during the aeration period. Additional aeration may be required as the outside air temperature drops, until you reach an acceptable AST, based on the grain moisture and temperature. Airflow rates of 1 cfm/bu are required to accomplish natural air drying, but this also takes time, and spoilage is a risk if grain is harvested at high moisture levels.

It is important to recognize that the smaller seeded crops like millet, sorghum and sunflower provide greater resistance to airflow than larger seeded crops like corn and soybeans. The same fans and grain depth that are used to aerate corn or soybeans may not adequately aerate the smaller seeded crops. Whether planning to aerate a stored crop or accomplish natural air drying, make sure the fans you are utilizing have the horsepower and design necessary to reach the airflow necessary to get the job done.

How wet can your crop be and still be safe to bin or pile on the ground? The answer lies in the AST, based on the moisture content and temperature of the grain and how long before you will be able to cool it or dry it to the recommended moisture content for safe storage.

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