DRAINAGE, IRRIGATION, AND DRY FARMING 123 



disadvantage of surface drains is that they occupy considerable 

 land, favor surface washing, and in fine-grained soils like clay 

 do not lower the water table to the depth required by growing 

 crops. Tile drains have the disadvantage of being expensive, 

 but they are efficient. Red-burned clay tile are commonly used 

 for draining land, and in recent years concrete tile have come 

 into limited use. 



The depth at which 

 tile are laid varies from 

 two to four feet, three 

 feet being the usual 

 depth. The more porous 

 the soil the deeper and 

 the farther apart the tile 

 may be laid. Some of 

 the essential things in 

 the laying of tile drains 

 are to have a free outlet 

 into a drainage channel, 

 to have tile that are hard 

 burned, and to have 

 them carefully laid with 

 uniform fall sufficient to 

 carry away the water. 

 The usual fall is from four to six inches per hundred feet, 

 although a fall of only two inches is allowable (Fig. 51). 



Ordinarily the tile used are a foot in length and are laid end 

 to end. The water enters through the cracks, or joints, between 

 the tile and does not pass through the sides of the tile. The 

 diameter of the tile used is commonly from four to six inches, 

 although where several lines of smaller tile empty into a main tile, 

 the main tile should be from eight to sixteen inches in diameter. 



150. Lands needing tile drainage. Tile are most extensively 

 and most profitably used on the prairie lands of Illinois and Iowa 

 and on the level land of Wisconsin, Indiana, Ohio, and New 

 York. Some level lands, however, are so fine-grained that water 



FIG. 50. Results of good and poor drainage 



On left, corn planted in pot having good drainage ; 



on right, corn planted in pot having poor drainage. 



Both pots had the same kind of soil and received the 



same amounts of water 



