Corn harvested at moisture contents up to 20 per cent can be stored safely during the winter with aeration, North Dakota State University’s grain-drying expert says.
Corn at 20 per cent moisture has an allowable storage time of about 25 days at 15.5 C, 50 days at 10 C, 90 days at 4.4 C and more than 300 days at -1 C, according to NDSU Extension Service agricultural engineer Ken Hellevang.
Allowable storage time is based on the kernel temperature and moisture content. It is reduced by about 50 per cent for each 10 increase in kernel temperature.
The estimated allowable storage time for 19 per cent moisture corn is about 35 days at 15.5 C. For 18 per cent moisture corn, it is about 50 days, and for 17 per cent moisture corn, it is about 75 days at 15.5 C .
Even corn at 16 per cent moisture needs to be cooled as soon as possible to enhance storage life, Hellevang says. Corn at 16 per cent moisture has an allowable storage time of about 70 days at 21 C, 120 days at 60 C and 230 days at 10 C. Charts showing allowable storage times for corn at these and other moisture contents are available at http://www.ag.ndsu.nodak.edu/abeng/postharvest.htm.
To extend the storage life of the corn, cool it as soon as possible. Corn should be cooled to about -4 to -6 C for winter storage.
Running the fan 24 hours per day will cool the corn to roughly the average outdoor air temperature. If the daily high is 15.5 C and the low is 1.6 C, the average is about 9 C.
Operating the fan just during the coolest 15 hours of the day will permit cooling the corn to a lower temperature, but will take longer. The final temperature if operating the fan from about 7 p. m. until about 10 a. m. might be about 5.5 C, assuming a high of 10 C and a low of about 1.6 C during the fan operation.
“Even though this difference seems small, a 10-degree decrease in grain temperature will roughly double the allowable storage time,” Hellevang says.
To estimate the time required to cool the corn, divide 15 by the airflow rate. For example, an airflow rate of 0.2 cubic feet per minute per bushel will cool the corn in about 75 hours (15 divided by 0.2). This cooling could take place during five nights of operating the fan 15 hours per night or during three days of operating the fan 24 hours per day.
Once the corn has been cooled, turn the fan off until the next cooling cycle.
Without aeration, corn should be placed into storage at 15.5 C or cooler and the temperature monitored closely. Respiration heating and solar heat gain on the bin may cause the grain temperature to increase.
Moisture migration will occur when the grain temperature is more than 20 warmer than the outdoor air temperature, so moisture migration is more of a problem in bins without aeration for cooling the grain. Convection currents will flow down the bin wall and up through the centre of the bin, causing a moisture increase in the top centre of the stored grain.
“Be prepared to move the grain if problems develop,” Hellevang advises.