Water and Watering 41 



Nearly all of the failures connected with the sub-irrigation 

 system can be traced directly to this point. Too fre- 

 quently the tile line is laid out by crude and inaccurate 

 instruments, such as a spirit level. The line of tile may be 

 laid at varying distances from 16 to 40 feet apart, according 

 to the porousness of the soil. 



Such a system should be laid out by means of a sur- 

 veyor's level and the stakes set as accurately as is done for 

 drainage systems. These various lines of tile are laid 

 out and then run to the main. The length of the laterals 

 will depend upon the convenience of the owner and the 

 character of the vegetables to be grown upon the soil. 

 In laying out such a system, it should be carried out 

 exactly as if it was intended for drainage only. The 

 length of the laterals will vary according to the contour of 

 the land and the desires of the owner. From 200 to 600 

 feet is usually considered a fair length for a lateral. The 

 tiles are usually made of clay and for the main part porous, 

 though glazed tile may be employed. The 3-inch size is 

 considered most satisfactory. 



The depth to which these are laid will vary from a few 

 inches to several feet. If it is necessary to have good 

 drainage during the rainy season, the tile can be laid 

 rather deeply in the soil. If, however, drainage is of second- 

 ary importance the tile may be laid higher. In any case 

 they should be laid not less than 12 or 14 inches below the 

 surface, since it frequently becomes necessary to plow to 

 this depth in a vegetable field. 



When these tiles are laid in the soil they should be on a 

 perfectly even slope. The joints between the tiles must be 

 protected by the use of some substance such as Spanish 



