The mid-October snowstorm will present some challenging issues for soybean producers moving forward in terms of getting the crop dry and then storing it, according to Ken Hellevang, an Extension ag engineer at North Dakota State University who specializes in the proper methods to dry and store crops.
The last National Ag Statistics Service (NASS) report issued before the storm indicated that as of Oct. 6, only 8 percent of the soybean crop in the state had been harvested. However, that same report indicated 92 percent of the crop was dropping leaves, which is a sign of crop maturity.
Freezing temperatures in some regions of North Dakota may have frozen some of the soybeans before they reached maturity, Hellevang noted.
“Those soybeans that froze before maturity may have a green color and will be smaller than mature beans after drying,” Hellevang said. “Also, field drying may be slower – beans may change color during dry-down and through time in storage. Green-colored beans will be discounted due to the required additional processing of the oil.”
Harvest shatter losses have been shown to increase significantly when mature beans undergo multiple wetting and drying cycles while standing in the field. Snowstorms, a rain event and even an overnight dew can increase the moisture content of the beans by several points, while the moisture content can be lowered on a day with low humidity or windy conditions.
It should also be noted that soybeans at 11 percent moisture have similar storage characteristics as wheat or corn stored at 13.5 percent moisture, so 16 percent moisture soybeans might be expected to store the same way as about 18.5 percent moisture corn or wheat. Furthermore, beans at 18 percent moisture would be similar to corn with a 20.5 percent moisture level.
Farmers are getting late enough into the fall that the amount of natural-air drying in bins is going to be limited. Hellevang said the equilibrium moisture content of soybeans for air at 40 degrees and 70 percent relative humidity is about 13.5 percent, which means drying soybeans with moisture content above 13.5 percent would be expected with this air condition. The drying rate will be slow with typical in-bin drying airflow rates.
For example, an airflow rate of cubic foot per minute per bushel (cfm/bu) is expected to dry 18 percent moisture soybeans in about 70 days, and increasing the airflow to 1.5 cfm/bu will reduce that time to about 47 days.
Increasing the airflow through the beans will also decrease the drying time proportionally, but that requires an increase in the horsepower of the aeration fans. Soybeans piled 22 feet high in a bin will require about 1 horsepower of fan for each 1,000 bushels of beans to deliver an airflow rate of 1 cfm/bu. To increase that airflow rate up to 1.25 cfm/bu will require about 1.6 horsepower per 1,000 bushels. An airflow rate of 1.5 cfm/bu will call for about 2.5 horsepower per 1,000 bushels of beans.
Soybeans at 16 percent moisture would require about 60 days at 1.0 cfm/bu., but by adding supplemental heat to raise the air temperature by 5 degrees will allow those 16 percent moisture beans to dry down to around 11 percent moisture in 55 days, according to Hellevang.
“The moisture-holding capacity of air is reduced at lower air temperatures,” Hellevang said. “As average air temperatures drop below 40 degrees, natural-air drying becomes inefficient and not economical. Adding heat causes the beans on the bottom of the bin to dry to a lower moisture content and would increase drying speed only slightly.”
Instead, soybeans can be dried in a high-temperature dryer, but the dryer temperature needs to be limited to minimize damage to the beans. He recommends consulting the dryer manufacturer’s guidelines for maximum drying temperatures. Typically, the maximum drying temperature for non-food soybeans is about 130 degrees, and even at that temperature, some skins and beans will be cracked. Keep the air relative humidity above 40 percent to minimize cracking of food-grade or beans that will be used for seed.
Hellevang outlined how producers can get a handle on the relative humidity levels they are experiencing during the drying process. With each 20-degree increase in drying temperature, the air relative humidity is reduced by one-half. Air at 50 degrees and 80 percent relative humidity will have relative humidity of about 40 percent when heated to 70 degrees. He recommends monitoring the soybean seed coming from the dryer and managing the dryer temperature based on the amount of damage occurring to the dry beans.
Food-grade soybeans and beans used for seed must not have damage to the seed coat, so natural-air or low-temperature drying is the preferred drying method. Seed beans should be dried at temperatures below 110 degrees, he stressed.
He also suggests cooling the soybeans to between 20 and 30 degrees for winter storage and completing the natural-air drying in the spring. You can start drying in the spring when outdoor temperatures are averaging about 40 degrees.
Prevent dryer fires
As with any commodity, there is always a risk of fire when drying the crop. Soybean pods and other trash can accumulate in the dryer and become combustible. As a way of lowering the risk of a grain dryer fire, Hellevang listed the following points to follow:
- Make sure trash does not accumulate in the dryer.
- Make sure soybeans continue to flow in all sections of the dryer.
- Monitor the dryer continuously.
- Clean the dryer frequently to reduce the potential for debris to combust.