Piling grain on the ground
June 01, 1999
by Teresa Acklin
The success of storing grain in outdoor piles depends on proper grain placement, quality requirements and aeration.
Outdoor piling of grain is a temporary or emergency grain storage practice used by grain elevator operators during bumper crop years. The success of this method will depend upon a combination of variables.
Some variables site preparation, pile dimension, use of aeration, moisture and cleanliness of grain can be controlled by the elevator manager. Variables outside the control of the elevator manager include weather (precipitation and temperature) and, in many cases, the length of time grain is left on the ground. Neighboring residences and businesses also should be considered to avoid dust, rodent, vermin and traffic problems.
Activities necessary to mitigate grain loss in outdoor grain piles fall into three categories: site preparation, grain placement and grain reclaim.
Site preparation steps include proper site selection, pad preparation, drainage and planning for the correct area necessary, based on estimated bushels targeted for outdoor grain piles. Grain placement, quality requirements and aeration will determine the success of storing grain in outdoor piles. Reclaiming grain provides an additional management step whereby grain may be segregated based on quality deterioration.
Selecting a naturally occurring high point on the elevator's property or at a site near the grain elevator offers a more economical option than bringing in material to fill low areas. Preparation of the ground pad involves stabilizing the existing base by adding strength and decreasing permeability.
Create a crown at the center point of the pile to provide a gradual slope away from the center. Slopes of 1% to 2% provide good drainage.
Reduced water permeability of the pad can best be accomplished by mixing lime, fly ash or cement in the soil prior to compaction. Check fly ash prior to use to ensure the absence of heavy metals.
The amount of compression necessary for a good pad should approach 95% of the standard proctor density. This value can be measured on site by the engineering firm using a density gauge.
The area surrounding the pad should be well drained to remove water running off the pile and pad. Most pads vary in surface area between one to two acres. One inch of precipitation on a 1-acre surface results in 27,152 gallons of water.
During site selection, determine how big an area to prepare by assessing how much grain is expected to be placed on the ground, the size and capacity of the conveying equipment and the type of grain placed on the pad. Trucks need one-quarter to one-half acre, or a diameter of 130 feet, to turn around in a circle without having to back long distances.
Circular piles typically are accompanied with stationary conveying equipment for placement and reclaim. Consequently, the discharge spout may be as high as 60 feet above the ground surface.
Frequently, grain is piled outdoors by portable augers powered by tractors, resulting in elongated, triangular-shaped piles. Piles higher than 25 feet may bury the auger and damage the undercarriage during movement. Overhead conveyors are recommended for deeper piles.
The ideal is to only place cool (50° to 60°F), dry (14% moisture), clean grain on outdoor piles. This enables the storage manager to maximize pile height and diameter, reducing the amount of surface area exposed to weather damage.
Quality tolerances are pushed with respect to temperature and moisture content when creating outdoor piles. Early harvest corn (maize) that requires drying may be placed on the ground at temperatures approaching 90°F. In such situations, grain elevator managers should consider making piles smaller to allow heat loss. Installation of an aeration system is critical if the grain is placed on the ground at temperatures above 60°F.
Build the pile uniformly to achieve maximum slope by keeping the drop distance from the spout to the pile at a minimum. The maximum angle of repose and pile height occurs when grain rolls down the side of the pile.
It is important to avoid creating hills, valleys, folds and crevices that will collect water. Sprouting and mold growth occur first in these areas.
Keep people and animals off the grain pile since divots in the pile collect water and intensify spoilage. Placing a temporary fence around the pile helps mitigate this problem.
Grain cleanliness also determines the success of outdoor piles. Segregation occurs during free-fall situations. Light material can be caught in convective currents or moved by winds during grain placement. Its concentration at any point in the pile can result in the grain experiencing self-heating and quality deterioration. Placing clean grain in outdoor piles helps slow quality deterioration.
Typically, ventilation ducts are positioned parallel to the long axis of rectangular piles. This type of design facilitates grain reclaim and directs cooling to the problem area of the pile, its core.
Ducts placed at the front and back ends of each pile should extend approximately 70 feet. For large piles, where the length of the long axis is greater than 200 feet, ventilate the pile core by running ducts in from the side and intersecting at the center of an 80-foot duct running parallel to the long axis, thus forming a T shape.
Use low velocity fans that provide approximately 0.1 cubic foot of air per minute per bushel to the pile core. Run fans as soon as cooling becomes available. Use of an inexpensive aeration controller will facilitate rapid cooling.
Quality deterioration in outdoor grain piles can occur rapidly. The reclaim process may necessitate further grain conditioning through aeration, drying or blending.
During grain reclaim, spoiled grain becomes commingled with sound grain, contaminating the entire amount with damaged kernels and commercially objectionable odors. Leaving spoiled grain along the base and edge of the pile on the ground as the rest of the pile is removed may help grain handlers avoid having to blend all the grain stored in outdoor piles.
Likewise, piles with the long axis pointing east-west may experience greater quality deterioration along the southern face of the pile. Segregating grain from the northern half of the pile from the southern half helps limit the amount of grain that requires additional conditioning.
Pick grain up from outdoor piles as soon as space becomes available. The costs and benefits of this practice, versus waiting until space becomes available for the entire pile prior to reclaim, should be weighed against penalties associated with quality deterioration.
This becomes difficult because discounts associated with odor are based on a yes/no decision. Thus, failing to reduce odor through conditioning and blending to below the discount level can increase the cost of outdoor piling of grain.
A partial budget analysis was performed to assess the additional costs of piling grain outside with and without aeration, as well as the fixed and variable costs associated with temporary storage and the construction of a corrugated steel storage bin (see box at right).
The first three scenarios are based on 1 million bushels of grain. Calculations reflect fixed costs associated with site preparation, ventilation equipment and construction. The fourth scenario is a summary of fixed and variable costs associated with a 750,000 bu corrugated steel storage system.
Variable costs associated with additional drying for ground piles, associated shrink and conditioning costs are included for scenarios one and two. Expenses for personnel, fumigation and grain quality evaluation for the four scenarios are not included since additional costs in these three categories vary widely between grain elevators.
Scenario one involved storing grain in an outdoor pile without aeration. This included preparing the pad, drying grain to 1% below the recommended safe storage moisture content for conventional storage, placing grain in the pile, reclaiming grain with a front-end loader and conditioning grain.
The cost of the pad preparation is amortized over five years at 8% interest. Maintenance costs of U.S.$1,000 per year are included, resulting in an average of $0.01 per bu.
Many individuals may not choose to make a long-term investment in preparing a pad for grain piling. Quotes for the cost of preparing a temporary site for one year (grading costs only) were similar to the cost of a permanent pad amortized over five years.
Conditioning grain after reclaim from outdoor piles with no ventilation included one pass through the drier ($0.01 per bu), approximately 300 hours of aeration ($0.005 per bu), turning the grain twice ($0.001 per bu) and 1% shrink associated with handling, drying and blending.
Scenario two involved storing grain in an outdoor pile with aeration. This scenario assumes that grain is dried to the recommended safe storage moisture content, thus a 1% shrink and added cost of drying is not included.
The additional expense associated with installing and operating a ventilation system was added. The bid provided used 18-inch diameter 16-gauge perforated corrugated full round ducts with shop-welded perforated end plates, connector band and tie-down. Also included in the calculation are 3 horsepower axial fans with guard and 3450 rpm TEAO motor, for a total cost of U.S.$31,340.
The reconditioning and blending costs were assumed to be half of those incurred by outdoor piles.
The third scenario represents use of temporary storage with aeration. The cost for temporary storage is amortized over five years at 8% interest. No additional drying or shrink associated with handling are included.
Aeration costs are approximately 25 times greater than scenario two, assuming that fans run continually to hold the tarp down on the top of the pile.
The fourth scenario involves a corrugated steel bin storage system. This does not include ventilation, additional drying, shrink or conditioning costs. Total expense for the corrugated steel bin is amortized over 15 years at 8% interest.
The economic analysis for different storage options will vary by elevator, the length of storage, pile size and quality deterioration resulting from outdoor piles. The feasibility of each option depends upon management expertise and personnel availability, as well as the ability to condition and blend grain.
Grain elevator managers should perform their own calculations based on individual quotes, marketing strategy and past ground storage experience.
|Comparison of surface area and volume for different heights|
| of circular piles, by commodity |
|Height (feet)||Grain||Angle of repose||Pile radius||Bushels|
| ||50||Corn||22°||124 ft||644,004|
|Wheat||25°||107 ft||479,526 |
|Sorghum||27°||98 ft||402,251 |
|60||Corn||22°||148 ft||1,100,000 |
|Wheat||25°||129 ft||832,581 |
|Note: Pack factor not included in bushel calculation.|
| Ground surface required for different pile heights, by commodity |
|15 ft||20 ft||25 ft |
|Note: Pack factor not included in bushel calculation.|
Estimated costs of grain storage methods
(in U.S. cents per bu)
Storing grain in an outdoor pile without aeration
Site preparation 1c/bu
Dry grain 3.5c/bu
Ground pile 0.7c/bu
Total cost: 11.5c/bu
Storing grain in an outdoor pile with aeration
Site preparation 1c/bu
Aeration preparation 3.1c/bu
Ground pile Aeration 0.7c/bu
Total cost: 1.5c/bu
Temporary storage with aeration
Temporary storage unit 0.7c/bu
Corrugated bin storage system
Steel bin 16c/bu
Total cost: 16c/bu