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Published October 09, 2009, 01:33 PM

Post-harvest tips for later maturing corn

The cool growing season has delayed corn maturity creating concern among corn growers. The biggest challenge with corn is removing the excess moisture after harvest. Last year, many acres remained in the field until the kernel moisture was low enough for a practical harvest.

By: Jim Stordahl, Clearwater/Polk Extension

The cool growing season has delayed corn maturity creating concern among corn growers. The biggest challenge with corn is removing the excess moisture after harvest. Last year, many acres remained in the field until the kernel moisture was low enough for a practical harvest.

The amount of drying in the field depends on corn maturity, hybrid, and moisture content, air temperature and relative humidity, solar radiation, and wind speed. The moisture content to which corn will dry is determined by the corn’s equilibrium moisture content, EMC, which is based on air temperature and relative humidity.

Standing corn in the field may dry about 0.3 to 0.4 percentage points per day during October and 0.15 to 0.2 per day or less during November. Corn at 35 percent moisture content on October 1 might be expected to dry to about 24 percent by Nov. 1 and about 20 percent by Dec. 1.

Therefore, corn moisture content at harvest will likely be in the mid-20 percent range again this year.

Field drying is normally more economical until mid to late October and mechanical high temperature drying is normally more economical after then.

Field drying is extremely slow during winter months and corn will only dry to about 20% to 21 percent moisture content based on the equilibrium moisture content for average monthly air temperature and relative humidity.

Corn in the field over winter in 2008-09 dried from 25-30 percent moisture in November to 17-20 percent when harvested in February and early March. Corn losses were generally small if the corn stalk was strong in November. However, accumulated snow and cover from the corn resulted in wet fields in the spring.

It is critical to provide aeration to keep the corn cool. Wet corn will deteriorate rapidly unless kept cool. Corn will deteriorate even with airflow, but without airflow through the corn it will increase in temperature resulting in rapid deterioration.

Condensation and icing occurs on bin vents at temperatures near or below freezing, so leave bin covers open to serve as a safety opening when operating fans near or below freezing temperature. There were numerous reports last year of bin vents freezing over and the fan pushing the roof up and damaging the bin roof.

Corn above 21 percent moisture should not be dried using natural air and low temperature drying to minimize corn spoilage during drying. An airflow rate of 1.0 to 1.25 cfm/bu is recommended to reduce drying time.

Because the drying capacity is extremely poor at temperatures below 35 to 40 degrees, little drying may be possible during the fall using a natural air system. Cool the corn to 20 to 25 degrees for winter storage and start drying in early April.

Adding heat does not permit drying wetter corn and only slightly increases drying speed. The primary effect of adding heat is to reduce the corn moisture content. Natural air drying in the spring is the most energy and cost effective method of drying.

Corn depth should be limited to about 20 to 22 feet to obtain the desired airflow rate for drying. Turn fans off during extended rain, fog or snow to minimize the amount of moisture moved into the bin by the fan.

Using the maximum drying temperature that will not damage the corn increases the dryer capacity and can reduce energy consumption. The amount of energy required to remove a pound of water is about 20% less using a drying air temperature of 200 degrees than at 150 degrees.

Be aware that high drying temperatures may result in a lower final test weight and increased breakage susceptibility. In addition, as the drying time increases with high moisture corn, it becomes more susceptible to browning. Dryer temperatures needed to be reduced below 200 degrees in 2008, to minimize the corn kernel damage.

Housekeeping during drying was critical during 2008 due to condensation occurring on the dryer creating a wet surface for debris to accumulate. The debris sometimes reduced airflow through the dryer reducing drying capacity and creating a fire hazard.

Propane cost for high temperature drying corn can be estimated using the following formula. Cost/bu. – pt. = 0.022 x propane price/gal.  For example, the drying cost is $0.022/ bu.-pt. if the cost of propane is $1.00, 0.022 x $1.00. It will cost about $26 for propane to remove 10 percentage points of moisture from 120 bushels of corn using $1 propane.

More fines are produced when corn is wet, because more aggressive shelling is required, which causes more kernel cracking and breaking. There is also more potential for stress cracks in kernels during drying, which leads to more breakage potential during handling.

In addition, immature corn contains more small and shriveled kernels.  Fines cause storage problems because they spoil faster than whole kernels, they have high airflow resistance, and they accumulate in high concentrations under the fill hole unless a spreader or distributor is used.

Preferably, the corn should be screen-cleaned before binning to remove fine material, cob pieces, and broken kernels.

Corn with damage to the seed coat and immature corn has a shorter storage life than mature corn. Therefore, cooling the grain in storage to about 20 to 25 degrees for winter storage is more important than for mature corn.

It is recommended to dry the corn a percentage point lower in moisture content.  More frequent checking of the storage is also recommended, and immature or damaged corn is not recommended for long-term storage.

For more information, contact me at 800-450-2465or stordahl@umn.edu.  Source: Ken Hellevang, NDSU Agricultural and Biosystems.

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