Storing Grain in Small Bins

GRAIN CAN be stored almost indefinitely with little deterioration in farm-type bins—those that hold 1,000 to 3,000 bushels— if it is kept dry, cool, clean, and free of insects.

When the Government acquired large surpluses of grain under the Agricultural Adjustment Act, the State agricultural experiment stations of Illinois, Iowa, Kansas, and North Dakota and several units of the Department of Agriculture started cooperative investigations to determine the best ways to store grain in farm-type bins. The investigators had problems, particularly with shelled corn, that had never before arisen, but as a result of their efforts many millions of bushels of wheat and shelled corn were stored several years with a loss of less than 1 percent that could be attributed to deterioration while in storage.

One of the first things they learned was the importance of having the grain dry. The maximum moisture content considered safe for the long-time storage of wheat and shelled corn are: Shelled corn, 13 percent; hard red spring wheat, 13 percent; soft red winter wheat, 12.5 percent; hard red winter wheat, 12 percent.

Lower average grain temperatures can be maintained by painting steel bins white or by shading them. Grain in wooden bins is less subject to extremely high temperatures at the walls. Temperatures of 135° F. were observed at the walls in unpainted steel bins at Hutchinson, Kans.

Dry, cool, clean grain discourages the development of insects. For the control of insect infestation, chief reliance must be placed on fumigation.  Grain dust and broken kernels contribute to a favorable environment for insect development and make fumigation harder. Grain that contains large amounts of foreign material, such as weed seeds, husks, and stems may deteriorate because of the higher moisture content of such materials.

The research men made many observations on the condition of grain stored in steel bins during the storage period and when the bins were emptied. The most serious damage to the grain was caused by water leaks at bolts joining wall and roof sheets, door jambs, ventilators, and such. Because of low foundations and poor drainage, some bin floors were submerged. If the floor or foundation extends laterally beyond the bin wall, drainage from the walls will be intercepted and is likely to enter and cause decay. Inadequate foundations led to settling so there was distortion of the bin and straining of the joints; in the northern sections wind-driven snow came through the cracks that resulted. Bins must have sufficient strength in foundations, floors, and walls to resist the pressure of the weight of the grain.

Making the bins leak-proof is largely the responsibility of the manufacturer, but farmers must consider the point when they buy and erect the bin. All joints between roof sections, wall sheets, and framing for openings require careful caulking at the time of construction. Bins already built can be improved by caulking. Bolts must be equipped with leakproof lead washers applied under the head and drawn to uniform tension.

The floor should be elevated enough above normal grade so that water cannot collect at the floor-wall junction. Water from melting snow banked against the bin wall may enter at this point; careful caulking there will minimize the hazard. Wall sheets must extend below the floor level to avoid a water table that will collect drainage from the walls.

Wooden bins provide good storage if they are kept tight. Single-wall bins are seldom tight enough to exclude moisture or retain fumigants satisfactorily. Bins that are not tight can be lined with heavy, reinforced, waterproofed paper, which must usually be replaced or repaired for each filling of the bin. Double-wall bins have proved to be superior to single-wall bins over a period of years because they keep out moisture and retain fumigants better. During the investigations, many other materials were tested and were found to be satisfactory if they met the requirements of structural strength, durability, and exclusion of dampness.

Drying in steel bins with perforated walls or floors or both and wind cowls of either the pressure or suction type was satisfactory, but wall perforations admitted moisture during driving rains, and the grain at the walls spoiled. The successful use of perforated walls is limited to the drier high Plains region.

Wood, steel, and concrete are commonly used for permanent grain-bin floors. Recent tests of these materials in 18 types of construction showed that 3 general types are satisfactory: Any floor supported on joists with free circulation of air beneath; steel floors on a fill of either earth or gravel to raise the floor above the surrounding grade and provide drainage away from the bin; concrete floors when equipped with a positive moisture and vapor barrier.

Insects attacking stored grain are not active at temperatures below 40° F., and multiply rapidly only at temperatures above 70° F. Insects are not a serious factor in the northern part of the grain-growing region, because temperatures of the grain do not rise high enough during the summer to permit the rapid development of infestations. The higher average temperatures south of the forty-first parallel favor rapid development, and insect infestation becomes a major hazard.

In southern Kansas, 22 management practices were evaluated with respect to their effect on wheat and their efficiency in preventing damage from insect attack. With the exception of the untreated check bins, all the practices maintained the original commercial grade until the bins were emptied. Three were found to be satisfactory in controlling insect infestation: Fumigating twice annually, in August and October; fumigating annually in September; turning, cleaning, and fumigating annually in September. Steel bins with white walls and roofs maintained average grain temperatures about 6° F. lower than unpainted bins.  The lower temperatures prevented the development of damaging insect infestation during the first 3 years but failed in the fourth. In evaluating the efficiency of the various management practices, the amount of insect infestation present on December 1 was taken as the criterion. The following tabulation presents a comparison of the insect infestation in bins of wheat under the three satisfactory management practices and that of the white bins and the untreated check bins:

For long-time storage the practice of fumigating in August and October and that of turning, cleaning, and fumigating in September were equally effective, but the added cost of turning and cleaning is not usually warranted. Fumigating in September has the advantage of reducing fumigation expense, but the rapid development of insects in August and early September just before fumigating causes unnecessary damage to the grain and leaves it more susceptible to subsequent infestation.

Besides eating the grain, insects cause other damage. In the fall, moisture accumulates in the cooled grain on the surface as a result of the normal upward movement of air from the warmer grain below. Insects create both moisture and heat, and they cause hot spots when they are concentrated in large groups. Severe infestation accelerates the upward movement of moisture and causes crusted and moldy grain at the surface so that all grain may be contaminated when the bin is emptied.

Fumigation offers the best method of controlling insects attacking grain stored in farm-type bins.

It is advisable to inspect stored wheat once a month during periods when the temperature of the wheat reaches or exceeds 70° F., and to fumigate it if found to contain one or more weevils or lesser grain borers, or 15 or more bran beetles per quart.

By fumigating in August and again late in September or October insect infestation will be destroyed; the wheat will cool normally in the fall and winter, and will usually remain in good condition until midsummer.

Inspection after severe storms is desirable; if leaks have developed wet grain should be removed, because migrating insects are attracted to high-moisture grain.

Shelled corn placed in long-time storage should be clean (that is, with less than 0.5 percent of cracked corn and foreign material). It is advisable to spray the surface grain with oil at the rate of 2 quarts to 1,000 bushels—an excellent preventive against insects that are likely to enter the bin during the summer. The oil should be a refined mineral oil of 100-200 seconds viscosity (Saybolt, 100° F.) and be free from objectionable odor.  Corn should be inspected with the same frequency as recommended for wheat and fumigated when found to be infested at the rate of one weevil or 25 bran beetles per quart.

The fumigant should be applied in a coarse spray uniformly over the surface of the grain. The most satisfactory method is to apply the fumigant from the outside of the bin by means of a power sprayer. A bucket sprayer may be used for small operations.

E. R. Gross is an agricultural engineer in the Bureau of Plant Industry, Soils, and Agricultural Engineering. He has farmed and taught farm mechanics in Nebraska, Colorado, and Mississippi. He was professor and head of the department of agricultural engineering in Rutgers University from 1922 to 1946. He has written a number of bulletins, articles, and papers on sprinkling irrigation, stationary spraying plants for orchards, tractor farming, use of explosives in agriculture, terracing, farm buildings and other subjects.

H. H. Walkden is an entomologist in the Bureau of Entomology and Plant Quarantine. He is a graduate of Massachusetts State College, and a veteran of the First World War. He has served in the Bureau of Entomology and Plant Quarantine since 1920. He has conducted research and published papers on cutworms, hessian fly, and insects attacking stored grain. He supervised the research on the insects attacking grain stored in farm-type bins.