Temporary Storage of Corn Grain
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By Steve Butzen, Agronomy Information Manager
Summary
- Existing grain storage capacity is not always sufficient to contain the volume of corn anticipated. Many growers will consider temporary storage structures as a solution.
- Requirements for successful storage in temporary structures are the same as in standard bins, including sanitation, pest exclusion, water-tightness, structural strength and aeration.
- If not already contained in the temporary structure, critical grain storage requirements must be added by the user. Even with modifications, expect grain losses of about 10 percent.
- Grain quality cannot improve in storage -- it can only diminish. For that reason, good initial grain quality is key to maintaining quality throughout the storage period.
- Achieving and maintaining "equilibrium" moisture throughout the grain mass is another key to successful corn storage. Maintain moisture at 15-16% or less for long-term storage.
- To prevent moisture migration due to temperature variations within the grain mass, air must be circulated through the grain. Airflow rates depend on grain moisture and other factors, but a rate of at least 0.1 cfm/bu is suggested.
- Experts suggest to check all stored grain every two weeks to assess condition and catch any problems early. Monitoring grain in less-than-ideal storage is even more imperative.
Introduction
Corn storage capacity, already insufficient in many areas, would be further stretched by the volume of corn anticipated this year. As a consequence, more corn will be stored in existing structures such as silos, machinery storage buildings, warehouses, or even livestock buildings. These structures can be used successfully for short-term storage of cool, dry grain if good management practices are used -- that is, if the grain is in good condition when placed in storage and the challenges of grain handling, aeration and pest control can be met. If grain in temporary storage is managed improperly, much of it could be lost to molds, rodents and insects.
Conventional corn storage bins have clear advantages: they are rainproof, vented, and resist insects, animals and other pests. Temporary grain storage structures may share all, or none of these characteristics. For successful storage, the critical grain storage requirements not contained in the temporary structure must be added by the user. Even so, some experts caution that grain losses or discounts may reach 10% and that the storage period may often be shorter than desired in temporary storage structures vs. standard grain bins. In fact, some temporary structures may only hold grain in condition for three to four months or less unless extensive modifications or improvements are made. A list of storage requirements is given below.
Storage Requirements
Capacity
When deciding whether to use an existing building for grain storage, estimate how much the building can hold. It may be enlightening to discover how few bushels some flat buildings can actually store, especially if ceilings are low or grain cannot be piled against the sidewalls. Formulas are available to calculate the volume of grain in rectangular or cylindrical structures, as well as in conical piles.
For more information review the following articles:
- Computations on Grain Stored in Various Configurations. Lancaster County Extension - University of Nebraska.
- Grain Storage Tips - Factors and Formulas for Crop Drying, Storing and Handling. University of Minnesota.
Sanitation
Both permanent and temporary storage structures must be sanitized prior to storage, but this process will likely be more difficult with temporary structures. Good sanitation practices will help avoid immediate insect infestation or disease inoculation of the new crop. The building should be thoroughly cleaned and all insects and previous grain, grain particles and feed removed. Be sure to clean under perforated floors and in aeration ducts and grain handling equipment as well as inside and outside of the structure. Consider fumigating any areas that can't be cleaned.
If the building previously contained manure, agricultural chemicals, or petroleum products, completely remove these materials so that the grain will not be physically contaminated or pick up odors that would result in downgrading. After thorough cleaning of the building and equipment, consider spraying the structure with an approved, residual-type insecticide.
See also:
Stored Grain Insect Pest Management. Purdue University.
Bird and Rodent Exclusion
Grain losses are unavoidable if birds and rodents have access to the grain. Inspect the storage structure thoroughly to determine how to keep these pests away from the grain.
Water-tightness
Check the building for water-tightness during or immediately after a heavy rain. Fix roof leaks if necessary. Be sure there is good drainage that directs water away from the structure rather than onto or under the floor. If the structure has a dirt or cracked concrete floor, it should be covered with 4- to 6-mil plastic to prevent moisture transfer into the grain.
Lateral Support
Most farm buildings are not built to withstand the lateral forces of stored grain and need to be reinforced. With some buildings, walls can be strengthened by cables or braces. In most buildings, however, it will be necessary to keep the grain mass from impacting the outside walls, especially if the grain depth is more than two feet at the wall. Using free-standing metal grain bin rings inside a structure is one way to contain the grain. Anchor the rings according to manufacturer recommendations. A 36-foot-diameter ring has a capacity of 800 bushels per vertical foot. Four rings (each 32 inches high) would have a capacity of 8,500 bushels. The cost of the rings is reasonable, given today's corn grain price. Aeration system designs are simple with these rings as well. Rings can also be built of plywood (see links below for more information.)
Other options to keep the grain mass away from the walls of the building include free-standing bulkheads and portable, self supporting grain walls constructed of plywood and lumber. These structures can be used to convert all or part of a building to grain storage. See engineering instructions that account for the force of the grain mass and the strength of the building materials to construct an adequate grain containment wall. An ag engineering publication available for this purpose is:
Temporary Grain Storage. North Dakota State University.
Grain Quality During Storage
Initial Quality
Grain quality cannot improve in storage -- it can only diminish. For that reason, good initial grain quality is key to maintaining quality throughout the storage period. Good grain quality begins in the field with managing insects and diseases and scheduling harvest based on field condition and proper grain moisture. Insect-damaged kernels may become diseased, or break with harvest and handling. Kernel rots that begin in the field will continue in storage if moisture and temperature are not strictly controlled. Corn harvested too wet may be badly damaged during combining.
Conventional grain bins are weather- and pest-proof, and have built-in aeration systems. Most temporary grain structures will need to be modified to provide these characteristics.
Careful grain movement and low-temperature drying are also important to minimize broken kernels and stress cracks that lead to eventual breaking. Intact kernels resist mold and grain deterioration. Broken kernels and "fines" block air movement in storage and lead to "hot spots" of spoiled grain in the bin. Rotary screens, gravity screens or perforated auger housing sections can remove broken kernels and fines prior to storage. If grain has poor quality, with excessive broken kernels, fines, kernels rots, and/or foreign material such as weed seeds or trash, it should likely not be stored. If stored, it should be screened and dried to at least one percent lower moisture content than that of good quality grain.
Moisture
Achieving and maintaining "equilibrium" grain moisture throughout the grain mass is the key to successful corn storage. Ideally, corn grain moisture should be maintained at 15 to 16% or below for long-term storage. Corn can be stored at higher moistures, but its shelf life will be reduced. Temperature is the other critical factor that determines shelf life of grain. Shelf life is a function of grain moisture and temperature as shown in Table 1. The storage times indicated in this table are not based simply on initial grain moisture, but on maintaining the indicated moisture by aeration. Unaerated corn may deteriorate three times faster than indicated in Table 1.
To prevent moisture migration within the storage structure, air must be circulated through the grain mass at a rate of at least 0.1 cfm (cubic feet per minute) per bushel of grain. This airflow rate applies when outside air temperatures are moderate during late fall, winter and early spring. This rate of 0.1 cfm is not sufficient to dry grain, but only to maintain the initial storage moisture content of the grain. To maintain grain moisture when grain is above 17% moisture or temperatures are above 70 F, airflow rates of 1/3 to 1/2 cfm/bu are required. Much higher airflow rates are needed to dry corn in storage.
Source: NebGuide G87-862-A, University of Nebraska.
Green cells: Under Nebraska weather conditions, corn temperatures cannot be maintained at these levels for the indicated length of time.
Yellow cells: Corn held at these temperatures and moisture contents requires frequent inspection and continuous aeration.
Note that corn at 16% moisture held at a constant 50 F can be safely stored approximately six months. The shelf life decreases about one month for every point of moisture above 16%. Also note how shelf life is drastically reduced by higher temperatures. At any given moisture content, the shelf life is cut in half for every 10 F increase in temperature.
The shelf life as defined for this table is the length of time that good quality, aerated corn can be stored before losing ½ percent of dry matter. Corn would lose some quality at this point, but should maintain its market grade. At conditions where the indicated shelf life is less than one month, visible mold growth may occur sooner than the times indicated in the table.
Filling and Unloading the Structure
For many temporary structures, it will be a challenge to move grain in and out of the building. Pneumatic grain conveyors and portable grain augers for this purpose may be available for sale, rent or custom hire. Despite the obvious downside, creating openings in the roof may often be the easiest way to get grain into the building. A bucket loader and portable augers can be used for moving grain out, although cables or other bracing may make this more difficult.
Grain Aeration
Even though grain is uniformly dry at the onset of storage, changes in temperature at the extremes of the grain mass result in natural movement of air and moisture. This "moisture migration" is the most common cause of problems in stored grain. Standard grain bins have a built-in ventilation shaft and fan system to keep grain aerated, control temperature and moisture migration, and prevent storage problems.
Grain in temporary storage structures must be aerated as well. This can be best accomplished with a well-designed system consisting of fans, supply tubes, and perforated ducts. The aeration objectives are identical to those of conventional bins: 1) to maintain the temperature of the grain mass within 10 to 15 F of the average outside air temperature; and 2) to maintain a consistent temperature (no more than a 10 F difference) within the grain mass.
Ordinary plastic drain tile doesn't have enough perforated area for good air movement, so use a product (metal or plastic) designed specifically for grain aeration. Your system should provide a minimum of 0.1 cubic feet of airflow per minute per bushel (0.1 cfm/bu) of grain. Proper fan sizing and system design are essential to achieve this desired airflow, so consult an aeration system engineer or ag engineering publication that specifically addresses this problem.
Positive pressure aeration system designs (air blowing into ducts and out the top of the pile) may work best for flat storage, but be aware of potential condensation problems under the roof. Minimize these condensation problems by providing adequate air exhaust area out of the building (at least 1 ft2 of open area per 1000 cfm of fan capacity) and plenty of air movement over the pile while the fans are running.
For more information review the following articles:
Management of Stored Grain with Aeration. University of Minnesota.
Selecting Fans and Determining Airflow for Crop Drying, Cooling, and Storage. University of Minnesota.
Tips for Temporary Structures
Silos
Unused concrete silos are an obvious target for temporary grain storage. However, users should realize that these structures were not designed for dry grain and consequently need to be modified. Most silos will need to be weather-proofed, as a weather-tight roof and chute, plus foundation drainage are essential. Silos will also need to be reinforced. For older silos, the number of hoops will generally have to be doubled for storing grain vs. silage. Newer silos use stronger materials, so check with the manufacturer about grain storage requirements. Silage blowers damage grain and cannot be used for loading or unloading. Silos must be unloaded from the center to avoid structural damage.
For more information review the following article:
Adapting Silage Silos for Dry Grain Storage. Purdue University.
Silage Bags
Silage bags are another commonly considered method of temporary grain storage. However, the surface of the bag readily transfers heat to the grain, which results in moisture movement. Heat and moisture create an optimum environment for mold development. For this reason, bags must be aerated to prevent spoilage of the grain. Some experts suggest using an 8-inch perforated pipe as an air inlet in the top of the bag and a 12-inch pipe as the return in the bottom of the bag. Air is pulled from the top to the bottom of the bag using a 12- or 14-inch fan. A 10-foot diameter bag will store about 60 bushels per foot of length. Bag length should be limited to 100 feet.
Large bales
Large round or square bales can be used as walls to contain outside grain storage. A circle of bales with a 40-foot inside diameter, 5 feet high, with grain peaked 9.3 feet higher than the bales in the middle and extending onto the tops of the bales, would contain about 8800 bushels of grain. When covered with plastic, this peaked grain arrangement provides a nicely sloped roof to drain water off the pile to the outside of the bales. Lining the inside of the bales with plastic will help to keep grain in and moisture out. Bales must be tied together with restraining cables or otherwise anchored to resist the outward forces of the grain.
Outside Piles Another option for temporary grain storage is outside piles. Outside piles are not unusual in corn-growing states when yields are high and corn volume exceeds regular storage capacity. Construct the pile on high ground crowned in the middle for drainage away from the pile. Use 4 to 6 mil plastic as a floor to prevent moisture transfer from soil to grain. The pile must be covered with plastic and aerated with perforated pipe to control temperature and moisture.
Checking Grain Condition
Regardless of whether corn is stored in conventional bins, temporary structures, or outside piles, it should be carefully monitored throughout the storage period. Even though temporary storage structures will likely be more difficult to check, it is even more imperative that grain in less-than-ideal storage be monitored regularly. Experts suggest to check grain at least every two weeks to assess condition and catch any problems early.
If any problems are detected, correct them immediately. This may require aeration, pest control, or in some cases, moving the grain. Good management can make temporary storage work satisfactorily in most cases if the challenges of providing aeration, managing pests and monitoring grain quality can be met.
References
Harner, J., T. Herrman and C. Reed. 1998. Temporary Grain Storage Considerations. Extension publication MF-2362. Kansas State University.
Herrman, T., C. Reed, J. Harner and A. Heishman. 1998.. Emergency Storage of Grain: Outdoor Piling. Extension publication MF-2362. Kansas.
Jones, D. and R. Grisso. 1995. Holding wet corn with aeration. Extension NebGuide G87-862-A, University of Nebraska- Lincoln.
Maier, D. and W. Wilcke. 1998. Temporary Grain Storage Considerations. Grain Quality Task Force publication GQ-38. Purdue University.