SUB-IRRIGATION AND SUBSOILING. 285 



should be conducted in zigzag courses, in furrows pre- 

 pared at the time of seeding, thus preventing washing, 

 and keeping the water as much as possible away from 

 the crowns of plants until it soaks into the soil. A head- 

 gate, d d, should be placed at the source of each of these 

 field laterals, and then it is possible for the farmer to so 

 regulate the supply in each part of the field that a suffi- 

 cient quantity may be obtained at the roots of every 

 plant, with very little or no water going to waste at the 

 ends of the field laterals. 



The Asbestine System. If the water supply be 

 limited, or difficult to obtain, this plan stands well at the 

 head. It consists of cement pipes, generally three inches 

 in diameter, but varying from two to four inches, that 

 are made in a continuous line in the bottom of trenches 

 with small openings at intervals, in which wooden plugs 

 or nipples with quarter-inch holes are inserted. A mod- 

 ified form for use in orchards, where the tree roots would 

 be likely to trouble by clogging the holes, has square 

 openings about six by three inches, over which a piece of 

 tile of a size that will fit evenly down over the opening 

 is laid. These tiles are laid from fifteen to twenty inches 

 below the surface, and although they will work if given 

 considerable fall, they distribute the water in a more sat- 

 isfactory manner if they have at best but a slight and 

 even slope. In the orchards they are laid between alter- 

 nate rows, and the holes are from fifteen to thirty feet 

 apart. The machine used in laying this system is illus- 

 trated in Figure 24, Chapter VIII. 



Another form of tile consists of short lengths of 

 cement pipe made in sheet-iron molds, which have 

 their joints closed with cement when they are laid. 

 These distributing pipes are often connected into sys- 

 tems of considerable size by being joined at one end to 

 a main supply pipe, which is generally of sheet iron 

 coated with asbestos. Sometimes what is known as 



