Naturally air-drying corn can work, but it requires a lot of airflow, and it typically takes a long time to air-dry corn in the Northern Plains when temperatures drop in the late fall, according to Ken Hellevang, NDSU Extension ag engineer and grain storage expert.
“We can put a fan on a bin and do aeration where we’re just moving enough airflow through to change the temperature of the grain,” Hellevang said. “And we can do that with a relatively small air rate.”
That allows producers to control the temperature of the grain, which is a storage management practice.
“However, if we’re going to try to remove moisture from the grain, we would need at least 1-1.25 cubic feet of air per minute (cfm) per bushel,” he said.
More horsepower and bigger fans are needed to achieve 1-1.25 cfm per bushel for air-drying corn. Since drying time is proportional to the airflow rate, at an airflow rate of 1.25 cfm per bushel, the drying time is about 35-40 days.
In addition, the depth of corn in the bin needs to be limited in order to naturally air-dry the grain effectively.
“Typically, corn depth of about 20-23 feet is about the limit as far as the depth that we can efficiently move that air through,” Hellevang said. “So as bins have gotten bigger, it’s easy now to put up a bin that might be 42 feet in diameter and 35-36 feet high. But we’re not going to be able to dry in that bin.”
The bin – and the fan – needs to be appropriately-sized in order to naturally dry corn. In addition, if the outside temperature is cold, moisture won’t be removed from corn.
“If we have an early harvest and we’re able to dry during half of October and we have an early delivery, we can do quite a bit of natural air-drying,” he said. “But, if we look at typical harvest dates, we’re usually looking at the latter part of October before we even start air drying.”
November temperatures are around 30 degrees in North Dakota, and that cold air does not hold enough moisture to accomplish in-bin drying.
Hellevang pointed out that in order to do air-dry corn in the state, “we typically are looking at maybe doing a little bit of drying in the fall, and we’re going to hold the corn wet over the winter and do the drying in the spring,” he said.
Once temperatures are averaging above about 40 degrees, the air is warm enough to pick up the moisture and do the drying.
“Natural air-drying is very limited in the fall,” he said. “North Dakota farmers have had a couple of dry years, and unless the weather pattern changes, we may be headed in that direction this year so that the corn will dry pretty well out in the field. Guys will start harvesting at 17-18 percent moisture and put it in the bin.”
If farmers take their corn off at 17-18 percent moisture early enough that they can run the fans for half of October and half of November, they can produce a major amount of drying.
“But even at the airflow rate of 1-1.25 cfm per bushel, it’s going to take at least four or five weeks of fan time to dry the corn,” Hellevang said.
Another limitation is that the maximum moisture content that air-drying can handle is about 20-21 percent moisture.
“The reason that 20-21 percent moisture is the maximum is because the grain could be spoiling faster than we can get it dry,” he said. “We would end up with spoiled corn on the top of the bin before we ended up getting the grain dried out.”
Grain drying moves from the bottom of the bin to the top, which is why after two weeks of air-drying, the grain on the bottom might be dry but the grain at the top will still be sitting at 17-18 percent moisture.
“Because of the limitations and because it takes a long time to air-dry, many guys don’t want to be limited as to when they can market that corn. They don’t want to be marketing wet corn over winter,” Hellevang said. “If we end up with a wet year where we’re saving that 23-24 percent moisture corn, that can’t be naturally air-dried.”
Fans controlled by a system that measures temperature and relative humidity and is properly programmed can move air through the corn to help preserve quality after harvest. Properly designed, installed, and managed fan controllers can help maintain the moisture and temperature of a crop at levels that prevent harmful bacteria and fungi growth and excessive shrinkage.
Natural air-drying is the most energy-efficient and probably the least expensive way to dry corn and other grain, but it comes with some limitations.
“It can work very well, but most guys who are seriously into corn are tending to dry with more of the high-temperature dryers. They will harvest it at 18 percent moisture and take it down to 15 percent with high-temperature drying,” he said.
At 15 percent, corn can stay at that percentage moisture through the winter.
“If we’re marketing in May or maybe even June, we just cool the corn down. It stores well at cool temperatures. Keep the corn cool in the bin as we go into the early summer and market that,” Hellevang said. “But if there’s a potential that the corn will be in the bin to be marketed in August, it really needs to be at 14 percent moisture or less. There is a potential for deterioration unless it is at 14 percent or less.”
A cover can be put on the fan to prevent the wind and the natural chimney effect from warming the corn and increasing the potential for deterioration of the grain during long-term storage.
“Producers need to pay as much attention to managing the grain during the storage period as they pay to producing the grain,” he said.
Hellevang said the new software from grain management companies where cables take the temperature of the grain and automatically start the aeration fans can be a good tool, but they require calibration and making sure their measurements are accurate.
“It’s a nice tool as long as the program helps them accomplish what is desired. Many of them are connected to kind of an outdoor weather station and determine if I run the fan now, am I accomplishing cooling in the long run? The temperature measurement is fairly accurate. But some of them indicate that they are measuring moisture content of the grain and they are actually measuring the relative humidity of the air and calculating the expected moisture. Relative humidity sensors don’t have the same reliability as our temperature sensors have,” he said.
The important thing is the producer still needs to be managing his grain and continually checking to make sure the equipment is operating accurately.
“The farmer still needs to understand what the strategy should be and then be monitoring and checking the accuracy of the equipment,” Hellevang concluded.
