Extension Update by Jenny Rees

Crop Update: Grateful for the harvest that’s been achieved thus far! Bean harvest slowed with humidity increasing moisture (which could also be a blessing after dropping so low), and corn harvest increased. Some pivots are running for newly seeded cover crops and small grains since we missed the rains. Couple reminders: Armyworm FAQ at: https://go.unl.edu/skx2. Also, check fields for stalk rot. I use a pinch test taking my thumb and first finger to ‘pinch’ a lower internode on 20 plants in a row. Obtain a percentage of plants that easily ‘give’ to determine % stalk rot. Video: https://youtu.be/7z75VN1c51Q.

Soybean moisture was last week’s topic of discussion. The Center for Ag Profitability released an article on the economics of crop harvest moisture at: https://go.unl.edu/o7hx and also provides a moisture loss calculation tool. Growers were pretty frustrated with yield losses due to overly dry beans and how this happens rapidly after a few hot days each year. By the week’s end, with increased interest in storing soybeans, several growers had asked about the economics and legality of grain storage rewetting.

Regarding the legality, while it is illegal to add water to any grain crop, it is legal to run aeration fans when humidity levels are high to increase moisture levels of beans. Dr. Ken Hellavang is an engineer at North Dakota State University that UNL also utilizes for our grain storage questions. He cautions to be aware of adding too much moisture as damage to bins can occur. He provides specific instructions at this website. A portion of his comments are shared below. By taking into consideration what he shares, economics of soybean moisture, and cost of running the fans, growers can determine the economics for your specific situations.

“Hellevang recommends producers operate aeration fans during weather with an average relative humidity of about 70 percent if they want to recondition soybeans to 13 percent during normal fall temperatures of 30 to 60F. If a fan runs continuously, the beans will lose moisture during periods of low humidity and gain moisture in high humidity. Be aware that the air will be heated 3 to 5 degrees as it goes through the fan, which reduces the air relative humidity slightly.

A reconditioning zone develops and moves slowly through the bin in the direction of the airflow, which is similar to a drying zone in natural-air drying. Depending on geographic location, not enough hours of appropriate temperature and humidity air may be available to move the reconditioning zone through the entire bin during the fall.

Reconditioning occurs the fastest when the airflow rate, cubic feet of airflow per minute per bushel (cfm/bu), is high and the air is warm and humid. It will be the most successful in a drying bin with a fully perforated floor and a fan that can deliver at least 0.75 cfm/bu. Even with this airflow, moving a reconditioning front all the way through the bin probably would take at least a month of fan operation.

Producers need to compare the cost of fan operation with the benefit of marketing at the desired moisture content. To estimate the cost of operating the fan, assume a 1 horsepower fan motor will use 1 kilowatt of electricity for each hour of operation. For example, if reconditioning the soybeans takes 30 days of fan operation, that is 720 hours. Achieving an airflow rate of 0.75 cfm/bu on a 42-foot-diameter bin filled 20 feet deep with soybeans would require a 15 horsepower fan. The cost to operate the fan, assuming an electricity cost of 10 cents per kilowatt-hour, is $1,080.

Increasing the moisture content from 9 to 13 percent would increase the quantity of soybeans by 1,019 bushels. (Multiply by price per bushel to determine economics compared to cost of operating the fan). You would need only a 3 hp fan to provide an airflow rate of about 0.25 cfm/bu, but reconditioning the beans would take about 90 days.

If you ran the fan just in periods of very high humidity, such as during fog or when the relative humidity is near 100 percent, the soybeans in part of the bin would be too wet to be stored safely. Mixing the wet layers with dry layers would reduce the spoilage risk and discounts for marketing wet beans. However, stirring increases the bean damage. Emptying the bin and moving the beans through a grain-handling system will provide only limited mixing because the majority of the grain comes from the top of the bin in a funnel shape with a center unloading sump.

A humidistat can operate the fan when the relative humidity will average about 70 percent. Even though the humidity level varies considerably during the day, it will average about 70 percent if the fan is operated for a time when the humidity is 90 percent and for a time when it is 50 percent. Setting the humidistat to operate the fan when the humidity exceeds about 55 percent would be a reasonable starting point. However, the humidity setting would need to be adjusted based on a measured soybean moisture content. To avoid wetting the beans to moisture levels unsafe for storage, add a second humidistat to stop the fan when the relative humidity reaches very high levels or use a microprocessor-based fan controller that monitors temperature and humidity, and runs the fan only when air conditions will bring the crop to the desired moisture content. A disadvantage of these options is that the fan does not run as many hours.”