18 SURFACE- AND SUB-IRRIGATION 



understand just how to lay the tiles so that the ends may not be 

 either too far apart or too close together, depending upon the 

 slant of the tiles and the nature of the soil. An inexperienced 

 person might better get an idea of this by first laying a line 

 upon the surface and, by pouring water through it, study its 

 action. Should there be danger of the tiles bursting from freez- 

 ing during the winter a proper drainage should be given at 

 certain points to draw the water off in the fall. By taking 

 advantage of this drainage the excessive moisture in the soil in 

 spring, and after drenching rains, can also be drawn off. 



The tiles can be so laid that the water is applied through a 

 single main feed-pipe ; or, by running the pipes above ground 

 at the end next the hydrant, each row may be watered separately. 

 The latter method requires a number of hydrants at convenient 

 distances along the garden so that pieces of ordinary garden 

 hose will reach all lines of tile. In order to get the best 

 results in the former case the ground should be nearly level. 



Even then still better results are secured by having not over 

 one half acre in each system, and a number of these systems 

 rather than one large one. The main feed-pipe should be not 

 less than two inches in diameter for an acre of land when 

 applied through a single system. This should be enlarged as 

 the area and number of systems increase. Where the practice 

 is to water a number of lines at the same time, a proportionately 

 larger supply pipe is needed. A one-inch pipe answers for 

 areas not over one half acre, a two-inch for an acre, and a pro- 

 portional volumetric increase as the area is enlarged. 



The reservoir should have sufficient capacity to irrigate the 

 area under consideration. In order to cover an acre of ground 

 to a depth of one inch, it requires 3,630 cubic feet of water 

 which is equivalent to about eight hundred and fifty barrels. 

 A similar quantity should be provided for sub-irrigation. If 

 the ground becomes very dry, it is advisable as in surface irri- 

 gation to use the maximum quantity to get beneficial returns. 

 If the surface is frequently cultivated, the loose soil prevents 

 evaporation and hence lessens the number of applications in a 

 dry time. By watering frequently rather than waiting until all 

 the reserve water is needed, only a portion of it will be 

 required and there will be a constant supply on hand ; for as in 



