Food Technology Information Center

Technology of Forage and By-Products Preservation

13. Sealing

Sealing is a very important part of the ensiling operation. The whole fermentation process, and the subsequent stability of the silage depend on the free oxygen environment. Any defect in sealing which permits air penetration will cause damage and losses. In the presence of oxygen, even at a very low concentration, less than 1%, the aerobic microorganisms become active and cause damage. In hot areas deterioration processes are more intensive, and especial care should be taken when sealing. In recent decades increasing amounts of silage are preserved in bunkers and in bales, and in both cases sealing is a problem: silage bales are susceptible to mechanical perforation, and in bunkers the top and the “shoulders” are sensitive locations. There is no doubt that the development of the plastics industry and of proofing materials have greatly improved the ability to achieve better sealing. Fig. 33

When sealing a bunker silo we have to prevent air penetration from the top and also from the walls. It is important to ensure that the walls are sound, since every crack will permit air penetration. Silage is an acidic material and is corrosive, a characteristic which especially affects the steel reinforcement in the concrete, which is susceptible to corrosion. Therefore, it is recommended to protect the walls, e.g., by painting; in some cases tar alone can be satisfactory.

The top layer of silage is usually covered with a polyethylene sheet, and such a sheet must be resistant to ultraviolet (UV) radiation. The thickness of the sheet to be used depends on the intended storage duration; the usual thickness is 0.15-0.20 mm, and such a sheet is not absolutely airtight but it protects the silage. To protect the sheet from the wind, it should be weighted down or covered with heavy objects such as old tires, gin tress, soil or any other suitable material Fig. 34 Fig. 35 and Fig. 36. The purpose of this covering is to keep the sheet in contact with the silage, but it is important to take care that these materials do not mix with the silage during feeding out, and get fed to the cows. When old tires are used, it is recommended to cut them in half transversely; the halves will still be sufficiently heavy to hold the sheet, but will be easier to handle. Also, whole tires can hold (rain) water inside, and so serve as an incubator for mosquitoes, or they can provide a refuge for rodents. In cases where animals or birds are liable to make holes in the sheet, it is necessary to protect it with an additional layer of strong netting Fig. 37.

There is practical evidence that sodium chloride (NaCl), when spread under the plastic sheet on top of the silage in a bunker silo, at densities of 3 kg/m2 over the surface and 3 kg/m along the shoulders, reduces the development of yeasts and molds.

As mentioned above, covering and uncovering the top of the silage in a bunker silo are labor-intensive operations, especially if the bunker is very big Fig. 38. In some areas in west Kansas farmers were accustomed not to cover the bunker, and to live with the knowledge that they sacrificed the top layer of silage. Is this an economy? The individual farmer must decide. In the same area an alternative solution comprised pouring a layer of a liquid, mainly molasses, but probably including some additional ingredients, onto the top layer of the silage instead of the plastic sheet. This layer remained elastic after drying, and looked good; it also resulted in feeding the upper layer. I am not sure if this method is still in use.

In the case of baled silage, it is important to handle the bales with care and to be wary of any sharp objects including stones. In a tower silo sealing is not a very big problem. Fig. 39, Fig. 40, Fig. 41, Fig. 42, Fig. 43, Fig. 44, Fig. 45, Fig. 46, Fig. 47, Fig. 48, Fig. 49.