30 THE POTATO 



entrance of damaging water upon one side, or by 

 facilitating its removal from the other. To ac- 

 complish one or both of these improvements 

 drains must be constructed which will give gravity 

 a better opportunity to remove surplus water. 



"When the drainage needs of our lands are ana- 

 lyzed it is evident that those that have good drain- 

 age owe it to: 



"1. Some natural condition that prevents the 

 entrance of an excessive amount of water; 



"2. A valley or ravine to serve as an outlet for 

 the water that does enter; 



"3. A surface slope to allow the escape of sur- 

 face water to the outlet, or 



"4. A subsoil sufficiently porous to admit of 

 some under-drainage. 



"Consequently, improvements in drainage con- 

 ditions consist of: 



"1. Protection ditches in the absence of natural 

 protection; 



"2. Outlet ditches where there are no valleys 

 or ravines; 



"3. Surface ditches to aid the limited slope in 

 removing surface water, or 



"4. Covered under-drains to facilitate the re- 

 moval of damaging water from wet subsoils. 

 Some areas need only one of these types, while 

 others need them all. 



"When water oozes into the dead furrows and 

 shallow ditches until they are kept wet almost 

 continually it is an indication that the land needs 

 tiling. The water table, instead of extending 

 horizontally from a tile, bends upward at a slope 

 that increases with the retentiveness of the soil. 

 It is evident that laterals may be farther apart in 

 sand than in clay, and that the deeper the laterals 



