GENERAL DRAINAGE INFORMATION 83 



medium and 2 to 2-^ is shallow. It sometimes happens 

 that in fields with uneven surfaces, or where it is diffi- 

 cult to get the proper amount of fall, the tile must be 

 laid in places as close to the surface as 18 inches. Tile 

 placed too near the surface are subject to freezing, and 

 freezing is almost sure to result in the cracking of the 

 tile, or in causing it to shale, which is likely to result 

 in its complete collapse. A depth of less than 3 feet 

 fails to give to the roots of most crops a sufficient 

 amount of room for development and forage. Greater 

 depth than 3 feet increases the effectiveness of drainage. 

 The champions of deep laying of tile offer three reasons 

 for the practice : (1) root room, (2) capillary water sup- 

 ply, (3) food development. 



114. The distance apart of tile drains. There is a 

 rather close relation between the depths to which the 

 tile are laid and the distance that may exist between tile 

 lines. Other things being equal, according to common 

 theory, the deeper the drains are placed, the greater the 

 distance that may lie between them, and vice versa. The 

 largest factor, however, in determining the distance apart 

 of drain lines is the character of the soil. 



In very heavy clays, it may be necessary to place tile 

 drains not over 30 feet apart, while in very open soils they 

 may be placed as far as 150 to 200 feet or more apart. In 

 muck soils they may be placed from 60 to 80 feet apart, 

 and in ordinary loams 70 to 100 feet. Eighty-five feet 

 apart is probably a fair average. 



Where soil is underlaid with a heavier subsoil, lying 

 so near the surface that the tile must be set down into it, 

 the drains must be placed closer together than would be 

 necessary if the subsoil more nearly resembled the soil 

 above in openness. (See Fig. 30.) 



