"The Art of Conditioning Soybeans: A Guide to Achieving Market-Ready Moisture Content"

In autumn, soybean moisture content dropped to 8% to 10% in many fields. Waiting for rain to replenish some of the moisture isn't an option for many farmers this late in the season. According to Ken Hellevang, North Dakota State University (NDSU) Extension agricultural engineer, there are a few other measures that can be taken to bring soybeans back from the brink of being too dry. Remember that adding water to any grain crop is unlawful, according to Hellevang. "However, it is allowed to condition the grain by operating fans pushing air through the grain when the air humidity is at proper levels, resulting in the grain moisture content being near the market moisture content," he stated.

The following news release was published by NDSU on the subject. We are publishing it here with minor changes.

Warm, dry weather can cause soybeans to be overly dry during harvest.

"When the soybeans are excessively dry, they lose weight and become brittle, increasing the possibility for handling harm," Hellevang explained. "In addition, reduced moisture concentrations cost manufacturers money."

 Farmers may want to condition soybeans that were harvested at lower moisture contents to bring the moisture content up to the market standard of 13%. On a 40 bushel-per-acre (bpa) yield, harvesting soybeans at 9% moisture content, rather than 13%, is equal to 1.8 bpa of lost weight. At $13 per bushel, that is $0.59 per bushel or $23.40 per acre.

Soybeans can be conditioned in the same way as grain is dried with bin fans by running fans during periods of optimal air temperature and relative humidity.

"To condition soybeans to 13% during regular fall temperatures of 30 to 60 degrees Fahrenheit, conditioning requires high airflow rates over many weeks utilizing air with an average relative humidity of roughly 70% to 75%," Hellevang added. "Be aware that the air will be heated 3 to 5 degrees as it passes through the fan, which will somewhat affect the relative humidity of the air."

Similar to a drying zone in natural air drying, a conditioning zone develops and progresses slowly across the bin in the direction of the airflow. Conditioning happens most quickly when the airflow rate, measured in cubic feet per minute per bushel (cfm/bu), is high and the air is warm and humid.

The moisture-holding capacity of the air is proportional to its temperature. At temperatures below roughly 40 degrees, the air has relatively little humidity and minimal conditioning happens. Conditioning will be most effective in a drying bin with a fully perforated floor and a fan capable of delivering at least 0.75 cfm/bu.

Regardless of how much airflow, it will most likely take at least a month of fan operation to move a conditioning front all the way through the bin. Most of the time, there aren't enough high-humidity hours in the fall to move a rewetting zone all the way through the bin. When the outdoor temperature rises over 40 degrees, the air conditioning may be turned back on. A 3-horsepower fan would enough to generate an aeration airflow rate of around 0.25 cfm/bu, but conditioning the beans would take about 90 days at that pace.

Farm owners should weigh the cost of using fans against the value of marketing at the optimal level of moisture. To calculate the cost of operation, assume a 1-horsepower fan motor consumes 1 kilowatt (kW) of electricity every hour of operation. For example, if it takes 30 days of fan operation to condition the soybeans, that is 720 hours. A 15-horsepower fan would be required to provide an airflow rate of 0.75 cfm/bu on a 42-foot-diameter bin packed 20 feet deep with soybeans. The expense of running the fan is around $1,296 assuming an electricity cost of 12 cents per kilowatt-hour. (720 hours times 1 kWh/hp times 15 hp times $0.12 kWh) By increasing the moisture content of 22,167 bushels of soybeans from 9% to 13%, the amount of soybeans would rise by 4.4%, or 975 bushels. This is worth $12,675 at a price of $13 per bushel, which is higher than the cost of powering the fan in this scenario.

If the fan is only turned on during periods of extremely high humidity, such as during fog or when the relative humidity is close to 100%, the soybeans in a portion of the bin will be too wet to store securely, by 20% or more. Mixing wet and dry layers would lower the risk of spoiling and provide discounts for marketing wet beans. Stirring, on the other hand, enhances the bean damage. Because the majority of the grain comes from the top of the bin in a funnel form with a central unloading sump, emptying the bin and sending the beans via a grain-handling system will only provide minimal mixing.

One alternative is to manage the fan manually or with a timer and operate it throughout the night and a portion of the day based on the observed humidity, although fan and humidity control is not as effective with this technique, according to Hellevang.

When the relative humidity is about 70%, a humidistat can activate the fan. Regardless of whether the humidity level changes greatly during the day, then that will average about 70% if the fan is turned on when the humidity is 90% and off when it is 50%. Setting the humidistat to turn on the fan when the humidity rises above 60% is a good place to start. Nevertheless, the humidity ratio would need to be modified dependent on the moisture level of the soybeans.

Add a second humidistat to stop the fan when the relative humidity reaches very high levels, above 90%, or use a microprocessor-based fan controller that monitors temperature and humidity and only runs the fan when air conditions would bring the crop to the appropriate moisture content. One downside of these alternatives is that the fan runs for fewer hours.

Hellevang advises farmers that soybeans expand as they absorb moisture, so a moisture content rise of more than a few points might produce enough pressure to harm the bolted connections of the grain bin or perhaps cause the bin to explode. If damage occurs during conditioning grain, the bin warranty may be invalidated.

One technique to relieve pressure is to unload some beans from the bin at least three times throughout the conditioning process. A negative pressure device can also be used to pull humid air down through the soybeans and remove the soybeans from the top of the bin as they are reconditioned. Another method for reducing pressure is to regularly mix the beans with a vertical-stirring auger. The number of broken or damaged beans increases as the beans are stirred. Unfortunately, these pressure-reduction approaches have not been thoroughly explored and are based on field experience with smaller bins.

This NDSU figure depicts how soybean moisture increases with relative humidity and how too much moisture can lead to dangerous storage conditions:

 

Equilibrium Moisture Values in Soybeans
	moisture in the air relation (percent)
Atmosphere	50	60	70	80	90
(F)	soybean Atmosphere content
32	10	11.8	13.7	16.2	19.8
40	9.8	11.5	13.5	16.0	19.6
50	9.5	11.2	13.2	15.7	19.4
60	9.2	11.0	13.0	15.4	19.1
70	8.9	10.7	12.7	15.2	18.9
80	8.6	10.4	12.5	15.0	18.7

According to this table, bean moisture increases as relative humidity increases. It also demonstrates how quickly a layer of soybeans may be rewetted to moisture levels that are too high for safe storage (the market moisture content is 13%).

Finally, conditioning soybeans to meet the market criterion of 13% moisture content can be accomplished with bin fans, but careful consideration of elements such as air temperature, relative humidity, and fan power is required. The running costs of the fans must be balanced against the possible increase in soybean weight and market value. To activate the fans, many methods like as human management, a timer, or a humidistat can be employed. Finally, the strategy used will be determined by the unique condition of each farm and the outcomes desired. According to North Dakota State University's Hellevang, adequate fan and humidity management are required to successfully condition the soybeans, and farmers should take the necessary efforts to guarantee they sell.