70 PRODUCTIVE FARMING 



They should always lead to the lowest portion of the field. 

 They must be gradually sloped to secure an even flow of 

 water in them. A fall of two feet in one thousand will be 

 enough for the flow of water if the tile pipes are laid care- 

 fully. The main drain should always occupy the lowest 

 part of the field, and the others may lead the water to the 

 main. 



Fia. 40. Laying drain tiles and testing the depth by measurement from level 



grade stakes. 



The distance of drains from each other and the depth 

 below the surface are governed by the character of the land. 

 On light, open soils, they should be deeper and farther apart; 

 on heavy land they should be nearer to the surface and closer 

 together. The mouth of the drain should be well protected, 

 and kept free and open. 



Drain Tile. The best underdrains are made by laying 

 drain tile pipes in the bottom of the ditches. These are 

 then covered with soil. 



