Dec. 4, 2009

Usually we can expect corn standing in the field to lose a point of moisture every three to four days during late September and early October. This year, however, drydown was much slower due to the high humidity and cooler than normal air temperatures.

Tens of thousands of acres of late planted corn in Nebraska had not reached physiological maturity (black layer) in late October when the crop was killed by freezing temperatures. That corn typically was above 30% moisture after the freeze. In some cases, especially when the corn had wounds from hail or insects, it was invaded by one of several fungal organisms (molds).

Many corn producers use natural (unheated) air to dry grain. Natural air drying takes a long time even under good drying conditions. This year it took much longer than usual due to cool temperatures and high humidity.

Producers usually wouldn't think of harvesting corn above 22% moisture, but this year many waited until November but still had corn at 28% moisture that they had to harvest before they lost it to a winter storm.

Recommendations for Winter Grain Drying

To keep this wet, stored grain from heating and losing quality in storage, producers should run the fan continuously whenever the wettest corn in the bin is above 18% moisture and grain temperature is above 50°F. Studies have been conducted under carefully controlled laboratory conditions with constant temperature and moisture content to establish the length of time corn can be held before it loses one-half of one percent of its dry matter. This is about the maximum dry matter loss one can suffer and still maintain the current market grade.

There are two rules of thumb regarding storage time.

1. When the corn is above 16% moisture, the shelf life is half as long at a given temperature for every two percentage points higher moisture content.
2. At a given moisture content, the shelf life is half as long for every 10°F increase in temperature. Grain above 16% moisture in a bin will deteriorate about three times as fast as the estimates in the table if it is not aerated to carry away the heat generated by the fungal growth.

Intermittent Fan Operation During The Cold Months

This year, some producers will likely not be able to get all of their grain dried to a moisture content considered safe for long-term storage (15% for corn and 13% for soybeans) before the weather gets too cold to accomplish enough additional drying to make it economically feasible to continue to run the aeration fans. (See the table on Equilibrium Moisture Content in Grain Storage Tips.)

If the moisture content of the corn in the bin is below 18% and the temperature of the grain is at or below 40°F:

• Consider intermittent fan operation during winter. This recommendation is contingent on the producer's ability and willingness to closely monitor the corn to detect the first sign of heating in the bin.

If the moisture content is above 16%:

• Use a grain thermometer to monitor temperature. (This is a sturdy thermometer attached to a metal rod that can be pushed several feet into the grain mass.) Probe several places near the bin walls and a couple of places near the center of the bin. Allow several minutes for the thermometer to equalize with the temperature of the grain before taking each reading.
• Run the aeration fan if the thermometer detects heating anywhere in the grain mass or if there is more than a 5-8º difference in grain temperature between any two spots in the bin.
• At the very least, start the aeration fan and immediately climb up and lean into the access hatch at the top of the ladder. If you detect a moldy smell or the air hitting your face is warmer than expected, or you see condensation on the underside of the bin roof on a cold day, this could signal a hot spot is forming in the corn. If you find any of these symptoms, continue aerating until conditions improve.
• If you have a stirring system in the bin, run a couple of rounds while aerating to break up wet spots and even out the moisture in the bin. If you don't have a stirring system and continue to see indications of a hot spot, unload enough grain to locate or break up the wet spot.

When the weather forecast calls for a period of warmer weather for several days, resume aeration when the equilibrium moisture content table indicates that some drying can be accomplished.

For example, if the air temperature is 50°F and the relative humidity is 60%, the table shows the equilibrium moisture content is 13.8%. If the wettest corn in the bin is a couple of points higher, you may want to kick on the fan to do as much drying as you can while you have the opportunity.

If you warm the grain mass above 40°F while drying, continue fan operation until the grain temperature drops below 35°F again. The goal is to get corn to 15% moisture and 30°F for storage from December through February.

If you can't get the corn to 15% moisture before discontinuing fan operation, it is critical that you get the temperature down to 25-30°F to arrest mold growth. Always push a cooling front completely through the bin before discontinuing aeration for longer than a few days. An estimate of the hours of fan operation required to push a temperature front through a bin of corn is 15 divided by the airflow rate in cubic feet per minute per bushel (cfm/bu). If your drying fan can produce 1.0 cfm/bu, it will take about 15 hours. If you have a storage bin with a small fan producing 0.2 cfm/bu, it will take 75 hours.
Tom Dorn
Extension Educator, Lancaster County