Are your soybeans too dry?


Did you harvest soybeans that were less than the market moisture content of 13%? That could cost you a lot of money when you sell the beans.

Tim Becker, Eddy County, N.D., Extension agent, says on a 40-bushel crop harvested at about 8% to 9% moisture you are losing about 2 bushels of weight due to the beans being too dry. “At $11 to $12 a bushel, that is around $20 to $25 per acre in lost moisture,” he says.

Adding water to soybeans to increase their moisture content is illegal, but you can boost the moisture content by aerating the beans with humid air, provided they have enough time and a high enough airflow per bushel, says Ken Hellevang, North Dakota State University Extension grain drying specialist.

The air is usually too dry over winter to raise the moisture level, but you can recondition beans in the spring by running aeration fans during periods of high humidity, Hellevang says.

If a bin is aerated continuously, the beans would lose moisture during periods of low humidity and gain moisture when the humidity is high. Therefore, you would need to make sure to operate aeration fans during weather with an average relative humidity of about 70% if you want to recondition soybeans to 13% during normal spring temperatures of 30 to 60 degrees F.

The rewetting zone

The moisture doesn’t change throughout the bin during reconditioning, Hellevang says. Instead, a rewetting zone develops and moves slowly through the bin in the direction of the airflow.

In beans with moisture contents of 10% or less, controlling the aeration fan so it runs only when the relative humidity of the air reaching the beans is greater than about 55% should result in rewetting, he says. One way to accomplish that is to use a humidistat to turn the fan on any time the humidity is above 55%. Another option is to run the fan only at night because that’s when humidity almost always is higher.

If you aren’t equipped to mix the soybeans after reconditioning, avoid wetting the beans to moisture levels at which they are unsafe to be stored.

To prevent excessive rewetting, add a second humidistat that stops the fan when the relative humidity reaches very high levels, or install a microprocessor-based controller that monitors temperature and humidity, and runs only when air conditions will bring the crop to the desired moisture content.

The disadvantage of these options is that the fan doesn’t run as many hours.

Reconditioning time primarily depends on the airflow per bushel and weather conditions. Reconditioning occurs the fastest when the airflow is high and the air is warm and humid. Reconditioning will be the most successful in a drying bin that has a fully perforated floor and a fan that can deliver at least 0.75 cubic feet per minute of airflow per bushel.

Even with this airflow, moving a rewetting front all the way through the bin probably would take at least a month of fan operation.

Soybeans swell when they absorb moisture, which could create enough pressure to damage bin walls, Hellevang says. One way to reduce that pressure is to use a vertical-stirring auger to mix layers of wet and dry beans. Another option is to unload some beans from the bin periodically.

To minimize damage during handling, use belt conveyors instead of augers or operate augers at slow speeds and keep them full. If using pneumatic conveyors, maintain proper air-to-grain ratios, make sure the conveying tubes have gentle curves and use a low conveying velocity. Also, minimize drop heights. Use bean ladders in situations in which beans may fall during conveying.

For more information about reconditioning, drying, handling and storing soybeans, see the NDSU Extension Service’s soybean production guide at www.ag.ndsu.edu/pubs/plantsci/rowcrops/a1172.pdf.

Source: NDSU Agriculture Communication

This article published in the December, 2011 edition of DAKOTA FARMER.

All rights reserved. Copyright Farm Progress Cos. 2011.