Some elevator operators recognize the greater value of dry grain and pay a higher price for grain that is drier than the official grain standards require. More grain dealers might well follow that practice.
SAFE STORAGE is aided by freedom from cracked kernels and foreign material, which provide food for insects and fill up the spaces between kernels and interfere with the natural movement of air through the grain. In one test with shelled corn, in which air under pressure was used, 5 percent by weight of cracked corn, chaff, and other foreign material reduced air movement by 19 percent. Because the kernels continually give off heat and moisture by respiration, slowing down of air movement through the bulk of grain tends to develop hot spots and caked grain. Even the slow air movement in clean grain due to convection currents helps keep it in good condition.
Cleaning is best done when small grain, soybeans, or other seeds are combined or corn is shelled by properly adjusting the sieves and air blast of the machine. It can be done later with a fanning mill or by gravity flow over screens. A rod-bottomed section for an elevator spout to remove shelled corn and similar material when cribbing ear corn is illustrated in Farmers' Bulletin 1976, Handling and Storing Soft Corn on the Farm.
TO BE SATISFACTORY, a bin must hold the grain without loss of quantity; exclude rain, snow, and ground moisture; afford reasonable protection against thieves, rodents, birds, poultry, insects, and objectionable odors, such as might be caused by fertilizers, chemicals, dusts, gasoline, or kerosene; permit effective fumigation to control insects; and provide reasonable safety from fire and wind damage.
Many farm storages do not meet those requirements. A survey of 7,000 farms in Georgia, for example, disclosed that 74 percent of the storages visited could not be fumigated effectively, 96 percent were not rodent-proof, and fewer than half gave good protection from the weather.
An examination by agricultural engineers of buildings used to store wheat and shelled-corn storages in six Midwestern States showed the importance of good foundations, floors, walls, roofs, well- constructed doors, and ventilator and roof-hatch openings in protecting grain. Even small leaks around a bolt without a lead washer in a metal roof may cause spoilage of 2 or 3 bushels of grain. Loose knots, split boards, or open joints in single-walled wood bins may allow leakage enough to spoil several bushels. Improperly flashed doors are other spots where leakage may occur. Floors that are too close to the ground may be flooded during heavy rains or by water backed up by snow and ice. Sometimes the top of the foundation is higher than the bin floor and catches water that finds its way into the grain. Concrete floors in damp locations should be raised well above the ground and protected by a vapor barrier (such as a layer of composition roofing under or on top of the concrete) to prevent rise of water vapor, which condenses in the grain and may cause serious spoilage.
SMALL GRAIN or shelled corn may be dried in batch or continuous driers before it is placed in the storage bin. Such driers consist of a ventilated container for the grain, a power-driven fan, a source of heat (usually an oil burner or a gas burner), and necessary handling devices and controls. Batch or continuous driers of a size to keep up with a small-grain combine or a cornpicker-sheller combination may cost $1,500 or more, depending on capacity, percentage of moisture to be removed, and the amount of construction done at home. They are rather expensive for the average farm, but they are good investments for farms that have large acreages of grains or seeds in areas where the grain cannot safely be left on the stalk until it is thoroughly dry. They could be used to advantage by groups of farmers.
The development of artificial drying methods and equipment suitable for farm use makes it possible to shell ear corn immediately after it is picked or to use the picker-sheller, a machine that leaves the cobs in the field. Corn can be shelled when the moisture content of the kernels is 25 percent or slightly more, although it must be dried immediately before placing in storage. Since shelled corn occupies only half as much space as ear corn, the cost of drying equipment may be offset by the saving in building cost. The method of field shelling, drying, and storage in bins instead of cribs may have special value in the South, where it is difficult to build cribs that can be ventilated well enough to dry the corn and then closed tightly enough for effective fumigation.
Drying grain in the bin is less efficient than drying with special driers, but the cost of equipment is usually lower. The ordinary method with small grains is to place a perforated or screened floor about a foot above the regular floor of the bin. Parallel rows of 8 by 8 by 16-inch concrete blocks may be laid on the floor, spaced 12 to 16 inches apart in each direction, and a 2- by 6-inch plank laid on top of each row of blocks. Special perforated and corrugated or ridged metal sheets are then laid over the 2 by 6's, thus making a continuous perforated floor. Air forced under the floor of the bin passes up through the grain. Hardware cloth supported on 2 by 4's, and covered with fly screen may be used instead of the perforated sheet metal.
The drying air may be heated or unheated. Drying with unheated air is slow, except when the atmospheric humidity is low and the temperature is above 60 F. For reasonably rapid drying, the air temperature should be above 80 and the relative humidity below 60 percent. In climates where atmospheric conditions at harvesttime are favorable, a heavy-duty electric fan or blower may give sufficient drying capacity, but under unfavorable conditions a unit that provides heated air is needed.
The best results are had when the thickness of grain on the perforated floor is not more than 2 or 3 feet. If air under sufficient pressure is available, drying can be done at depths of 6 or even 10 feet, depending on the moisture content of the grain and the resistance it offers to passage of air. For example, air passes through shelled corn and oats much more easily than through wheat. The wetter the grain the thinner the layers should be. From 5 to 10 cubic feet of air per minute per bushel of grain are needed when drying at temperatures between 60 and 130 F., which are about the limits for farm drying. Detailed information about equipment and methods for drying shelled corn and small grain in bins are described in Farmers' Bulletin 2009, Storage of Small Grains and Shelled Corn on the Farm.
Ear corn may be dried in almost any type of crib. One way to distribute the drying air is by using a large canvas on the side of the crib to form an air duct. Methods of drying corn are described in Farmers' Bulletin 2010, Storage of Ear Corn on the Farm, and Circular 839, Mechanical Drying of Corn on the Farm.
Ventilation is desirable to cool grain in large bins or flat storages in autumn and thus prevent "migration of moisture" from the warm interior to the cool top layers of grain. If the grain in large bins is not cooled rapidly, convection currents are set up by the temperature difference between the warm grain in the central part of the bin and the cool grain around the edges. The upward air currents at the center of the grain mass carry moisture to the cool top layers of the grain, where it condenses and may cause molding. The condition is particularly bad when insect infestation is present on account of the warmth and vapor given off by their respiration. Winter cooling of the grain helps to destroy insects in it. The amount of air needed to cool grain is much less than to dry it, and comparatively small fans and air ducts are adequate.
To PRESERVE GRAIN from insect damage, one must think first of prevention of destructive outbreaks.
Most of the insect pests of stored grain and seed have short generations, a high rate of reproduction, and long-lived individuals characteristics that cause great fluctuations in numbers. Under favorable conditions, outbreaks are apt to occur suddenly.
The immediate causes of such outbreaks are the factors that affect the rate of egg laying, the rate of development, the death rate, or the longevity of the insects. The more important factors are moisture, temperature, food supply, and human activities. We cannot do much to alter the weather or change the existence of large supplies of food, but we can make grains less susceptible to insect attack by the use of efficient cleaning and drying equipment and by the application of fumigants and good storage management practices.
AFTER PROMPT HARVEST, followed by drying when necessary, grain and seed should be stored in clean, insect-free, weather-proof storage on premises from which nearby sources of insect infestation have been eliminated. Steel bins that are easy to clean and can be made tight by calking are best for storage of small grains, shelled corn, or other seed.
Wooden bins should be thoroughly cleaned and the walls and floors treated with a residual spray before they are refilled. This will kill most of the insects that emerge from burrows and cracks in the woodwork. Steel bins should be thoroughly cleaned. It is not necessary to spray the entire bin, but it is advisable to spray around the door frame where insects may be concealed. Wooden-crib elevator bins should also be sprayed.
For spraying bins use 2.5 percent of DDT, TDE, or methoxychlor by weight as emulsions or water suspensions, or 5 percent of piperonyl butoxide and 0.5 percent of pyrethrins by weight as an emulsion. The sprays should be applied at the rate of 2 gallons per 1,000 square feet of surface area. They may be applied safely and easily with an ordinary garden sprayer or a power sprayer.
Farm-stored small grains should be fumigated within 2 weeks after placing in the bin in the South and within 6 weeks in the central part of the United States. In the North, fumigation after storage may not be necessary but is good insurance against infestation. Fumigants and dosages recommended for small grains in farm storage are given in the chapter, "Fumigating Stored Foodstuffs," page 345.
In the Northern and Central States, one fumigation will probably be enough. Properly applied, the fumigant will destroy insect infestations present and will protect the grain from serious insect invasion until fall. Winter weather will then cool the grain to levels where insects are inactive.
Farm-stored grain should be inspected periodically to detect dangerous insect infestation. In Northern and Central States during the warmer months and in the South throughout the year, grain that has been in storage a month or more should be inspected every 2 to 4 weeks and refumigated if serious infestations are found.