LAND DRAINAGE 



67 



How Drainage Warms the Soil. — Drainage lowers the 

 water in soils. As the water goes downward, the air from 

 above is drawn into the soil. In warm weather the air will 

 thus warm the soil, increase chemical action, and aid in the 

 growth of soil bacteria. Plant growth is thus hastened. 



Drains Ventilate the Soil. — This not only warms the soil 

 but also gives it the necessary oxygen and removes the 

 harmful gases. 



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Fig. 39. — Drainage deepens the feeding area for roots and reduces the suffer- 

 ing at time of drought. The view at the left shows free water just under the roots. 

 When drought comes the roots are left so near the surface as to let them dry very 

 badly. See centre view. The view at the right shows the deep root system 

 allowed by tile-drainage. 



Where Drainage is Needed. — There are several kinds 

 of places where it would be wise to put in artificial drains 

 of some kind: — 



1. Flat lands which are too wet because of the overflow 

 of streams at time of heavy floods. 



2. Bogs and marsh lands which hold the free water too 

 near the surface most of the summer season. 



3. Large, flat areas having clay subsoils. 



4. Depressions in hillsides which hold the water coming 

 from the land above. 



5. Fields which are to be flooded at certain times for 

 special crops, such as rice and cranberries. 



Principles of Underdrainage. — The value of under- 

 drains depends upon the free passage of water through them. 



