Temporary storage may be needed this year to protect grain until it can be moved into more permanent storage or sold. The length of time grain can be held in storage depends on the moisture content of the grain, the temperature of the grain, and whether the grain can be kept from heating by means of aeration.
Corn needs to be less than 15% moisture in order to be held in storage for extended lengths of time without aeration. Aeration is used to keep grain from heating and to cool the grain mass to slow the formation of molds. If sufficient volumes of air can be constantly pushed through the grain mass to prevent heating as a result of mold growth and respiration within the grain mass, grain at higher moisture contents can be stored for a time.
Corn at 16% moisture held at a constant 50 degrees F can be safely stored approximately six months. The shelf life decreases about one month for every point of moisture above 16%, (with sufficient airflow to maintain the grain at a constant 50 degrees F).
The shelf life is also reduced by higher temperatures. At any given moisture content, the "shelf life" is less than half as long for every 10 degree F increase in temperature. Comparing corn at 16% moisture content, the shelf life (with aeration) is 186 days at 50 degrees, 81 days at 60 degrees, and 45 days at 70 degrees. NebGuide G87-862, Holding Wet Corn With Aeration presents a chart showing the "Shelf Life" of grain over a range of moisture contents and temperatures.
Airflow rates as low as 1/10 cfm/bushel have been successfully used to hold grain at or less than 16% moisture during the cooler part of the year. Operating the fan continuously over long periods will slowly cool grain when outside air temperatures are below grain temperatures.
Greater airflow rates (1/3 to 1/2 cfm/bushel) are recommended to aerate grain that is placed into storage at moisture contents above 17% or temperatures of over 70 degrees F. Much higher airflow rates are required to dry grain as opposed to maintaining temperature. For more information on drying grain refer to NebGuide G85-760 Natural Air Corn Drying or NDSU publication AE-701 Grain Drying .
Modifying Existing farm buildings
If temporary/emergency grain storage is needed, putting a crop in a building is better than putting it out in the open. If bin space is full, pole barns and machine sheds can provide good grain storage if they're prepared correctly and not overloaded. An excellent reference on this subject is NDSU AE-84, Temporary Grain Storage by Kenneth J. Hellevang.
Ordinary machine sheds are not designed to withstand the loading that grain will exert on the wall. (Grain exerts a lateral force on a wall of about 23 pounds per square foot per foot of grain depth). This pressure tries to push the bottom of the wall out and also causes extra forces at the top of the wall. Posts, trusses, and post-to-truss connections can fail when buildings are improperly reinforced for grain storage. Manufacturers often can provide building strength information, especially for steel-frame structures.
If the building was not designed to hold grain, grain should not be piled more than 2 to 3 feet deep against the wall. For deeper grain depths, building walls will need to be modified to protect the sheet metal from the pressure of the grain on the wall. Depending on the application, stud walls with plywood sheathing may be either constructed between the posts or in front of the posts to protect the sheet metal from the lateral pressure created by the grain. In most applications, the posts, post to truss connections and bottom truss cords will need to be reinforced or strengthened to withstand the pressure of the grain on the walls.
It is strongly recommended that the building manufacturer or a structural engineer be consulted before attempting to modify an existing structure for grain storage. An alternative to modifying the building would be the use of steel bin rings placed inside an existing structure to hold grain. Another option would be the placement of portable, self-supporting bulkhead walls in the building to protect the building walls from the lateral pressure. The design of portable bulkheads has changed from earlier recommendations. Revised plans are included in NDSU publication AE-84, Temporary Grain Storage.
Grain that is dry and cool with properly designed aeration systems can be heaped (piled higher in the middle of the building) to increase the capacity for temporary storage. If the grain does not drop long distances from the unloading auger to the pile, corn will naturally seek an angle of repose of about 21 to 23 degrees. (21 degrees is about 4.5 inches of rise per 12 inches of run and 23 degrees is about 5.2 inches of rise per 12 inches of run).
Buildings used for grain storage should be in a well-drained site. Lay a sheet of 6-mil or heavier plastic on the floor to reduce the migration of moisture from the soil or through cracks in concrete floors into the grain.
Using aeration to cool grain and maintain uniform temperatures within the grain masses is extremely important to preserve grain quality; therefore a well-designed aeration system using tubes or ducts is essential. Cool temperatures minimize mold growth, limit moisture migration and control insects. An aeration airflow rate of at least 1/10 cubic foot per minute per bushel is recommended for grain that is already dry.
If grain must be piled outside on the ground,drainage is crucial. The pile should be on high ground and the earth crowned under the pile. Placing plastic on the ground absolutely is essential to keep soil moisture from migrating into the grain. Cooling the grain prior to piling improve the chances for success.
Cover piles with plastic or a tarp to reduce wetting by rain and snow, and to minimize damage by wind and birds. A smooth surface will aid in drainage. Position and extend the cover so water is channeled away from the pile.
Condensation under the plastic cover may cause severe problems unless controlled with aeration. Air must flow near the plastic cover to reduce condensation and carry the moisture away. Temporary hoop structures which provide shelter while maintaining an air space between the plastic and the grain should alleviate some of the rewetting problem that could occur as a result of condensation on the plastic cover. If a rectangular pile is made to store grain, orient the pile north and south to allow the sun to dry condensation off the sloping sides of the cover.
Temporary containment structures
Large round bales can be used to form a temporary "bin" for outside storage. Grain exerts a pressure of 23 lbs/sq-ft per foot of depth on the wall. Assuming a bale diameter of 72 inches and a height, when stood on end, of 60 inches and assuming that 1/3 of the surface of the bale is adjacent to the grain; each bale would have an outward force of over 1800 lb. acting on it. This would be enough force to move the bale out of position if not held in place with restraining cables. Therefore the bales need to be placed in a circular pattern and kept from spreading by enclosing the structure with at least two cables held in place vertically with stakes every 20 feet or so.
Plastic along the inside of the bales will help keep grain in and water out. Peak the grain so it flows onto the top of the bales to form a smooth, drainable cover. The plastic or tarp should drape over the top of the bales, so the water flows to the outside of them. A 8800 bu temporary containment made from large round bales would require a bale structure that measures 40 feet in diameter (inside), 5 feet high at the wall, grain peaked in the middle 9.3 feet higher than at the bales and extending over the tops of the bales 2 feet beyond the interior wall to enhance water drainage.
Aeration Duct Spacing and Sizing
Perforated ducts should be the proper size and have the proper spacing to meet minimum requirements. Airflow rates, aeration duct sizing, and fan selection are beyond the scope of this paper. For more information on engineering an aeration system obtain a copy of MidWest Plan Service Publication number 29,Dry Grain Aeration Systems Design Handbook.
Another temporary storage
option that holds some promise is the use of large plastic silage bags.
Grain going into these bags should be dry and cool (under 15% and 60 degree
F.) . If the normal system that is used for filling the bags with silage
is used to fill the bag, expect some kernel damage. A system specifically
designed for handling dry grain is available from the manufacturer that
reportedly greatly reduces grain damage.
2 Gerald Bodman is an Extension Ag. Engineer -Livestock Systems, UNL/IANR
3 David Jones is an Associate Professor, Biological Systems Engineering, UNL/IANR