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Grain Storage Systems


Sam McNeill, Extension Agricultural Engineer


Soybean Harvest Drying and Storage - Fall 2017 (PDF)


It has been estimated that an average operator will leave from 2 to 4.5 bushels of soybeans per acre in the field (5 to 10% loss). Considering the price of soybeans (~$10/bu), reducing losses from 10% to 5% results in a savings of $22.50 per acre. Measure harvest losses (4 seeds per square foot = 1 bu/ac loss) and strive to keep them below 3%.

Seed Moisture at Harvest

The moisture of the bean and the hull determine the best time for harvesting soybeans. The range is from 9% to 20% moisture content (wet basis), but research at the University of Missouri has indicated that soybeans can be harvested at 15% moisture content and that there is less seed damage at higher moisture contents. Seed damage increases as the moisture content decreases, so harvest promptly if the moisture drops below 13.5%. UMO research indicated that there is considerably less visible damage to the soybean when it is harvested above 13.5% moisture and it should be harvested prior to reaching 11.5% to reduce seed damage. Rewetting after maturity results in a higher percentage of cracked seed coats when harvested.

Operating the Combine

Adjustments in order of importance are ground speed, cutterbar height, reel position and speed, threshing, and cleaning.

  • Ground speeds above 2½ - 4 mph can result in high losses at the header.
  • Keep the cutterbar as low as possible for field conditions to reduce stubble loss.
  • Set the reel axle 6 to 12 inches in front of the cutterbar. Run the reel about 1.25 faster than the ground speed to reduce shattering.
  • Soybeans should be cut as close to the ground as possible.
  • Cylinder speeds above 500 rpm result in higher seed crackage. Follow the operator's manual for the initial settings for the cylinder speed and concave/rotor spacing.


Soybeans are usually dried with natural air (no heat), although a small amount of heat (5 to 10 degrees) can be added when the relative humidity is above 80% (see Table 1). Generally, a drying temperature below 110°F is recommended. Drying time is dictated by airflow rate, with a minimum of 1 cfm/bu recommended. The University of Minnesota Extension Service website can be used to estimate the airflow rate for a given fan-bin combination. For example, a 10 hp axial fan can provide 1 cfm/bu in a 30-ft diameter bin of soybeans that is 20-ft deep (11,300 bu), or 3 cfm/bu at 8-ft of depth (4500 bu).

Moisture Content

Soybeans should be dried to a level that matches the storage period. If sold before spring they should be dried to 13.0%, but if held through the summer they should be dried to 11.0% to keep the relative humidity of the air in the void space (between seeds) below 65%. Be careful not to over-dry soybeans (see Table 2). With today’s price, drying a point below the market level (13.0%) amounts to 11.4 cents per point. For this reason, consider installing an automated fan control system that can be programed to operate the fan according to outside air conditions.

Clean Grain

Ideally, weed seeds, stems, and other foreign material should be removed from soybeans before they are stored. Accumulation of trash in small pockets in the grain bin can cause heating and may lead to caking and spoilage. Normally, when cleaning soybeans, particles removed are larger than the seeds. Alternatively, core the bin daily when filling or after the bin is full to remove the pocket of trash that tends to accumulate in the center of the bin.


Soybeans should be cooled after storage and about 10 degrees each month afterwards to about 35 degrees. Seal the fan(s) with a tarp or heavy plastic sheet after the last cooling cycle to reduce wind driven air movement through the grain.

Estimate the amount of time to run the fan for a complete cooling cycle by dividing 15 by the amount of airflow in cfm/bu. For example, only 15 hours of fan operation is needed at 1 cfm/bu, but 150 hours are needed at 0.1 cfm/bu, which is considered the minimum rate for aeration.  The University of Minnesota Extension Service WINFANS program can also be used to estimate the airflow rate at different depths for a given fan-bin combination.


Know the dangers associated with flowing grain and exposure to grain dust and educate all workers on the farm of these hazards. See UK publication AEN-39 for more details (http://www2.ca.uky.edu/agc/pubs/aen/aen39/aen39.pdf). Never enter a grain bin while the unloading auger is operating because the moving grain can pull a person below the grain surface in less than five seconds. Always disconnect the electrical power for motors on unloading augers or remove the belt drive when entering a bin of grain and work in pairs with a person on the ground who can call for help if needed. Personal protective equipment for bin inspections includes a climbing harness and respirator at minimum.


  1. Bushchermohle, M.J. and S.G. McNeill. 1997. Drying, Handling and Storing Soybeans in Tennessee. In: Soybean Production in Tennessee. UT Ag Ext Service. PB-1608. http://trace.tennessee.edu/utk_agexcrop/51/
  2. Hamilton, H.E., O.J. Loewer, Jr. and D.G. Overhults. 1973. Harvesting, Drying and Storing Soybeans. UK CES AEN-25. http://dept.ca.uky.edu/agc/pub_prefix.asp?series=AEN
  3. Helsel, Z.R. and H.C. Minor. 1993. Soybean Production in Missouri. Univ. of Missouri Extension Service. Pub. G4410. www.extension.missouri.edu/p/G4410.
  4. Hurburgh, C.R. 2008. Soybean Drying and Storage. Iowa State Univ. Extension. PM-1636. https://store.extension.iastate.edu/Product/Soybean-Drying-and-Storage.
  5. Willis, J.B. 1997. Combining Soybeans Efficiently. In: Soybean Production in Tennessee. UT Ag Ext Service. PB-1608. 

Preventing Post-Harvest Losses - 2017 Kentucky Grain Storage Update

Kentucky grain farmers produced a record level of soybeans, and near-record level of corn in 2015 and 2016, primarily due to timely, ample rains (Tables 1 and 2, respectively). In most years, grain is stored on-farm between 1 to 9 months, and Kentucky farmers maintain a sound reputation of producing high quality products for feed, food, and fuel use throughout the southeastern U.S. and around the world.

Average commodity prices for 2015 and 2016 place the total value of grain crops at just over $1.8 billion for both years. Post-harvest losses of 1% or more are not uncommon during storage and can result in subsequent discounts by the elevator or grain buyer, which represents a minimum of about $18 million in lost income statewide. Hence, prudent management of stored grain is essential to protect product value and quality during handling, drying and storage.

The Biosystems and Agricultural Engineering Department's extension education program is dedicated to providing timely, research-based information that emphasizes proven storage management tools, safe handling practices, and energy efficient drying methods that help producers and elevator managers maintain high quality grain after harvest.

Between 2005 and 2015, 30 million bushels of additional on-farm storage were constructed, bringing the state’s total to 201 million bushels (Fig. 1). When added to the total off-farm storage (76 million bushels), the current total capacity in the state is 277 million bushels. Additionally, grain production has been expanding in some areas of the state where storage capacity is limited so the potential growth for conventional storage systems is increasing.

Interestingly, the portion of grain stored on Kentucky farms (73%) is higher than the national average (55%), and higher than any other state in the Midwest (Fig. 2).