258 FEEDS AND FEEDING 



at the top of the silo where the mass is exposed to the air, but if the 

 silage has been well packed and wet down, the impervious top layer of 

 rotten material, which soon forms, prevents further entrance of the air. 

 All doors must fit tightly, else the silage will spoil about the openings. 



2. Cylindrical shape. In the early silos, which were rectangular 

 structures, it was exceedingly difficult to pack the mass in the corners so 

 that it would not spoil. With the devising of the cylindrical silo by King 

 at the Wisconsin Station* this serious trouble was overcome, thereby 

 greatly advancing the practice of ensiling forage plants. The cylindri- 

 cal silo has now been commonly adopted, for besides the advantage of 

 having no corners, it provides the largest cubic capacity for a given 

 amount of building material, and the sides are strong and unyielding. 



3. Smooth, perpendicular, strong walls. Unless the walls of the silo 

 are smooth and perpendicular, cavities will form along the walls as the 

 mass settles and the adjacent silage will spoil. The walls must be strong 

 and rigid, for during the settling of the silage a great outward pressure 

 is developed. This increases with the depth of the silo and, according to 

 King, 5 reaches 330 Ibs. per square foot of wall surface at a depth of 30 

 feet. After the silage has fully settled this lateral pressure ceases. 



4. Depth. The early silos were shallow, and even tho the forage was 

 well-tramped it was often necessary to weight the mass down to force out 

 the air sufficiently. By making the silo deep the great pressure com- 

 pacts all but the upper layers so that the losses thru fermentation are 

 reduced to a minimum. The fact that the losses of nutrients are heaviest 

 in the upper layers and surface of the silage is another reason for having 

 the silo deep, because the loss per ton of total contents is thereby reduced. 

 At the Wisconsin Station 6 King placed about 65 tons of green corn for- 

 age in an air-tight silo in 8 layers, and determined the loss in each layer, 

 after standing from September to March. The dry matter lost in the 

 respective layers was as follows: surface (eighth) layer, 32.5 per ct. ; 

 seventh layer, 23.4 per ct. ; sixth layer, 10.3 per ct. ; fifth layer, 2.1 per 

 ct. ; fourth layer, 7.0 per ct. ; third layer, 2.8 per ct. ; second layer, 3.5 

 per ct. ; and bottom layer 9.5 per ct. While the surface layer lost over 

 32 per ct. of its original dry matter, the average loss in the first 5 layers 

 from the bottom was less than 5 per ct., and the loss for the whole silo 

 only 8.1 per ct. 



407. Types of silos. Silos may be constructed of wood, solid concrete, 

 concrete blocks and staves, brick, stone, glazed tile, or sheet steel. In the 

 semi-arid regions pit silos, preferably with cement lining and curb, are 

 extensively used, but these are impracticable in humid climates. In the 

 southwestern states silos are sometimes built of adobe, reinforced with 

 wire and plastered with cement. The choice between the various types 

 of construction, all of which make good silos when well-built, will depend 

 upon local conditions. 



This work can present only the primary principles relating to silo 

 4 Wis. Bui. 28, issued July, 1891. 5 Wis. Bui. 83. 6 Wis. Bui. 83. 



