278 IOWA DEPARTMENT OF AGRICULTURE. 



For these reasons the circular silo has become much the more popular, 

 until at the present time we seldom see any other form being constructed. 

 Relative to size, it should not be less than thirty feet deep, because the 

 greater the depth the greater the downward pressure, resulting in a more 

 efficient expulsion of air from between the particles of cut corn; and as 

 the completeness with which the air is excluded determines the keeping 

 quality of the silage, importance of depth is revealed. Further than this, 

 the greater the downward pressure the greater amount of silage can be 

 stored in a cubic foot of space. And equally important is the fact that 

 silage capacity gained in depth rather than in diameter makes it possible 

 for a greater depth of top surface to be fed off daily. Silage exposed to 

 the air for two or three days begins to mould and spoil, and experience 

 teaches us that for satisfactory results from one and one-quarter to three 

 inches, according to climatic conditions, should be fed off of the top 

 each day. 



It has been estimated that the feeding surface in the silo should be 

 about five square feet per cow in the herd. Thus, for a herd of 30 

 cows 150 square feet of feeding surface or a silo 14 feet in diameter will 

 be necessary; 40 cows, 200 square feet, or a diameter of 16 feet; and a herd 

 of 50 cows, 250 square feet, or an inside diameter of 18 feet. Many have 

 made the mistake of building silos with too large a diameter and have 

 experienced a considerable loss from not being able to feed a sufficient 

 amount from the top each day to prevent molding. It should always be 

 kept in mind that better results will be gained from two small silos 

 rather than one extremely large one, providing they are properly filled. 

 The depth necessary for the silo can be readily obtained after determin- 

 ing the proper diameter to permit the feeding of a definite number of 

 inches in depth to each cow. For instance, two inches are to be fed off 

 each day; 180 days feeding would require 360 inches or 30 feet in depth. 

 In determining the material for the silo, the manner in which the 

 silage will be preserved, the longevity of the silo and the cost should all 

 be considered. For wooden silos it is doubtful whether or not cheaper and 

 at the same time more efficient silos can be made than the commercial 

 stave silo made of Oregon fir or sound northern white pine. Precau- 

 tions should be taken, however, to demand that the staves be seasoned, 

 free from sap and dead knots. Live knots or those found in staves that 

 have been sawed from live trees are not so objectionable because they re- 

 main taut in the wood for many years, and often material containing these 

 can be bought for less money because of their presence. Of late cement 

 silos are attracting considerable attention and undoubtedly they are the 

 coming silo, especially on farms where plenty of good gravel is accessible. 

 In the past their cost, together with the fact that the silage did not keep 

 so well in them as in a wooden silo, has prohibited their use, but with 

 improved construction devices and a knowledge gained of preparing the 

 inner walls the cost will be lessened and methods placed in vogue for pre- 

 serving the silage to the extent that the length of time which they will 

 last will be a controlling factor and surely they will come into quite gen- 

 eral use. 



Whether of wood or cement, the silo should rest on a strong foundation 

 set deep enough in the ground to prevent the frost from heaving it out of 



