Research Highlights

Research Highlights
Moisture Content is Important for Optimum Quality When Storing Soybeans

Photo: United Soybean Board

By Carol Brown

Many times, necessity dictates a change in action. When the soybean trade embargos were instituted a few years ago, farmers had to store soybeans longer than usual. This led to the question of how long and under what conditions soybeans could be stored to retain optimal quality. 

North Dakota State University Professor Kenneth Hellevang began looking into this question and found more issues that needed to be addressed.

“There are tables created for allowable storage of corn and soybeans that show parameters for length of time, moisture levels, and temperature,” Hellevang explains. “But when I compared the tables, the similarities between corn and soybean were glaringly obvious. The soybean table seemed to be created by subtracting two percentage points from the corn parameters. Of course, that gives us an estimate, but this is not based on solid research.”

The agricultural and biosystems engineering professor is conducting a research project that looks at soybean storage. He and his team stored soybeans for 12 months under four moisture levels to measure mold growth, germination, and seed quality. This work is supported by the North Dakota Soybean Council. Hellevang’s goal is to adjust or confirm the data in the soybean storage table so farmers can have the most accurate information when it comes to keeping their beans at the highest quality.

Hellevang and his team conducted the research project on the NDSU campus in chambers that can replicate North Dakota seasonal temperatures across 12 months. They stored two common varieties of soybeans at moisture levels of 11, 13, 15 and 17%. Some of the soybeans were held at a constant temperature, and some soybeans experienced a sequence of temperatures from 72 to 40 to 5 degrees F, mimicking a typical North Dakota meteorological year.

“The market standard for storing soybeans is at 13% moisture,” says Hellevang. “That works well for essentially six months of storage, where we’re harvesting and storing soybeans during the relatively cool months. But we have found this didn’t work as well for longer term storage.”

Hellevang examined the soybean equilibrium moisture content. When a seed is put into a particular environment, such as 70 degrees F and 60% humidity, the seed will come to a certain moisture content that is in equilibrium with the condition of the air. He selected a humidity level of 60% in this experiment to limit mold growth. He found that the equilibrium moisture content for soybeans in these conditions was just below 11%, rather than the market-standard 13%. 

He also tested storing soybeans at 15 and 17% moisture because in many years, soybeans are harvested under wet conditions, and this amount of moisture in the crop is a possibility. 

He and his team found that soybeans with 17% moisture content do not store well, as was expected. They saw significant mold development within one week at room temperature (72°F). It spoiled even quicker than they thought, Hellevang says. They saw significant mold growth at 15% moisture in the warmer temperatures as well. 

Hellevang paid particular attention to the soybeans with 13% moisture because of the market standard. They found that the soybeans stored very well at this moisture percentage for up to six months, but going into summer temperatures, they saw the amount of mold increase. 

They also measured soybean germination rates, which may be a factor for growers in areas that use soybeans for feed. At 15 and 17% moisture at 72 degrees F, germination rate decreased after eight weeks of storage. The stored seeds showed signs of secondary infection, and mold spores were present on germinated seedlings as early as the fourth week of storage.

“If soybeans are harvested and it’s 40 or 50 degrees out, farmers can get by storing them in those cooler temperatures,” he explains. “But anything stored in warmer temperatures and with 15 to 17% moisture content just doesn’t work. This emphasizes my recommendation that soybeans need to be closer to 11% moisture if the beans will be stored through the summer.”

They have finished collecting the data on the 12 months of storage, and now Hellevang and his Ph.D. student are analyzing the information. He hopes it will be wrapped up by this fall, and he will be able to make more accurate recommendations to farmers for optimum soybean storage. 

Published: Oct 10, 2022

The materials on SRIN were funded with checkoff dollars from United Soybean Board and the North Central Soybean Research Program. To find checkoff funded research related to this research highlight or to see other checkoff research projects, please visit the National Soybean Checkoff Research Database.