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Grain Storage: Climate Inside The Bin

January 2, 2019

Grain storage begins with harvest, as drying and storage go hand-in-hand.

Usually artificial drying allows:

  • Harvesting when the crop is ripe and mature
  • Proper storage that preserves seed quality.

Even though storage will not necessarily improve the quality of the harvested grain, it helps maintain the existing quality. Harvesting at a proper moisture level is important. So is reducing handling and mechanical breakage of the seed/grain where possible.

Grains harvested at ideal temperatures may allow for temporary storage without further drying, however, the recent rain and cooler temperatures on the horizon may not provide that option of drying down naturally to the right moisture content.

The ideal moisture for soybean harvest is 13 to 15 percent. Soybeans can be harvested as soon as seeds are mature and foliage is dry, but seed above 18 percent moisture does not thresh well.

When storing grain for extended periods of time, as in months up to a year, it is important to dry the grain quickly, and minimize humidity and temperature fluctuations in the bin.

Soybeans should be at 11 percent moisture for long-term storage.

These recommendations are lower than typical harvest or market moisture, but they will help regulate temperature and minimize mold growth and pest infestations while preserving grain quality.

Soybeans are often more fragile than corn and may be susceptible to more cracking of seed coats or the seed itself.

Many newer bins have technology that can monitor conditions both inside and outside of the bin. These bins may even have switches to operate fans when needed. Without this technology, however, it is up to the grower to ensure that grain is stored in ideal conditions.

Although uncommon, a fan cover can be a simple addition to any bin. Covers help reduce temperature fluctuations due to air brought into bins by wind. This can prolong grain storage by maintaining cool temperatures, especially in long-term storage situations.

Roof vents are equally important in maintaining bin temperature to allow hot air above the grain to escape. Vents can also help prevent grain from increasing in temperature.

A 10 degrees Fahrenheit decrease in temperature can approximately double the number of days the grain will remain in good condition in storage with humidity staying the same.

Natural Air, Low Temperature, or High Temperature Drying?

There are three ways to dry grain: using natural (unheated) air or by high or low temperature dryers.

North Dakota State University Extension suggests that soybeans can be natural air dried after harvest in October to about 12 percent moisture content. From mid-October to mid-November, natural air drying can reduce soybeans to about 13 percent moisture content.

As an example, after using natural air drying to 12 percent, low temperature drying can be used to increase the temperature by 5 degrees to dry the grain to 11 percent for long term storage.

When reaching moisture levels below 11 percent, damage to the seed and seed coat is likely to occur. Once the ideal moisture content is achieved, these conditions should be maintained in the bin.

Seed soybeans should not be dried at temperatures above 100 degrees Fahrenheit as it will affect their germination.

Care should be taken with temperatures above 110 degrees Fahrenheit with a batch dryer.

For a continuous flow dryer, temperatures above 130 degrees Fahrenheit should be avoided.

Soybeans are more sensitive to high drying rates. Research has shown that seed coat and seed breakage occurs more often at high temperatures, with as much as 50-90 percent breakage.

Equilibrium Moisture Content

Another important factor to consider is Equilibrium Moisture Content, which is the retained moisture content by the grain when exposed to specific temperature and relative humidity for a prolonged period.

High temperature in a low relative humidity environment dries the grain faster. A good technical reference for Equilibrium Moisture Content can be found at University of Arkansas Research & Extension (see Table 1 & Table 2).

These tables can help determine if some heating will be effective to reduce moisture to meet the EMC necessary for long-term storage.

Aerate to Maintain Temperature

Moisture and aeration for temperature control are key players in long-term grain storage.

Stored soybeans should be aerated to maintain a grain temperature of 35-40 degrees Fahrenheit in the winter (assuming about 60 percent relative humidity), and 40-60 degrees Fahrenheit in the summer.

In warm weather, bins should be checked once a week for heating or spoilage. In cold weather, every two weeks is sufficient.

Source: South Dakota State University