SOIL IMPROVEMENT 69 



The tile pipes should be very strong and haxd, so they 

 will not rot in the soil. They should be smooth inside to 

 avoid clogging. The ends should be clean cut so they will 

 fit together closely. A very common length for each piece 

 is twelve inches, but sometimes they are longer than this. 



The joints are open but are usually covered with sods, 

 rocks, broken tile or other material to help keep out the fine 

 soil. Sections of drain pipe are placed as close together as 

 possible and the openings are very small (Fig. 40). 



Water enters drain-pipes at the joints. The pipes carry 

 away only the free water and the capillary moisture is left 

 in the soil for the use of plants. If the pipes should lead 

 through a drier soil, the water would there flow from the 

 pipes into the soil. 



REVIEW. 



1. Give several ways in which drainage may help the soil. 



2. Give two methods of draining land. 



3. How does drainage warm the soil in the spring? 



4. How does drainage reduce suffering at time of drought? 



5. Give five kinds of places where drainage is needed. 



6. Give several points to be observed in making underdrains. 



7. What does distance between lines of tile depend upon? 



8. What things help to determine the depth at which to lay drain 

 tiles? 



9. Describe good drain tiles. 



10. How does water enter a line of tile? 



References. — U. S. Farmers' Bulletins: 158, How to Build Small 

 Irrigation Ditches; 187, Drainage of Farm Lands; 263, Practical Infor- 

 mation for Beginners in Irrigation; 373, Irrigation of Alfalfa; 399, Irriga- 

 tion of Grain; 404, Irrigation of Orchards. 



CHAPTER VIII. 

 SOIL IMPROVEMENT. 



The farmer should do what he can to improve soils, as 

 natural causes work too slowly. The depletion of a poor 

 soil may be due to the natural causes. Fields that are on 

 hillsides may be badly washed and gulhed by running water 



