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Don't Trust Moisture Meters Now

Don't Trust Moisture Meters Now
It's too cold and the corn is too wet for accurate measurements. Here's how to get the right reading.

Because its cold and corn moisture contents are high, don't trust your moisture meter during corn harvest this year.

"Moisture meters will not provide accurate readings on corn coming from a high-temperature dryer," says Ken Hellevang, NDSU Extension agriculture engineer. "The error will vary depending on the amount of moisture removed and the drying temperature, but the meter reading may be about 2% lower than true moisture."

To determine the amount of error, check the moisture of a sample, place the sample in a closed container for about 12 hours and then check the moisture content again.

Moisture meter errors increase as corn moisture contents increase, so readings above 25% should be considered only estimates.

In addition, moisture meters are affected by grain temperature. If the meter does not measure the grain temperature and adjust the value automatically, then the adjustment must be done manually.

Even if the meter does it automatically, cool a sample in a sealed container to room temperature before measuring the moisture content. Then compare the moisture content of the room-temperature sample to the initial sample to verify that the adjustment is done accurately.

Moisture meters normally are not accurate when grain temperatures are below about 40 degrees. Place the corn sample in a plastic bag or other sealed container, warm it to room temperature and then measure the moisture content.

Moisture shrink and test weight are other measurements that are important to producers.

Moisture shrink is the reduction in weight as the grain is dried. The formula for calculating the percentage of moisture shrink is [(Mo-Mf)/(100-Mf)] x 100. In that formula, Mo is original moisture content and Mf is final moisture content. Thus, the moisture shrink of drying corn from 25% to 15% is [(25-15)/(100-15)] x 100, or 11.76%.

The moisture shrink factor is the reduction in weight as the grain is dried 1 percentage point. The formula to determine the moisture shrink factor is 100/(100 minus final moisture content). Therefore, the shrink factor of drying corn to 15.5% is 1.1834. The moisture shrink of drying corn from 20.5% to 15.5% would be 5 x 1.1834, or 5.92%.

Normally, corn test weight increases about 0.25 pound for each point of moisture removed during high-temperature drying. However, the increase in test weight is affected by the amount of mechanical damage during harvest and the gentleness of the drying.

Due to the high mechanical damage involved with harvesting, corn with 25% to 30% moisture levels and high drying temperatures used in 2008, frequently no increase in test weight occurred during drying. Little or no increase in test weight will occur on immature or frost-damaged corn.

Source: NDSU Extension Communications

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