[377] SCIENTIFIC MANUAL. 91 



"Water, charged with carbonic acid and oxygen, is con- 

 stantly circulating up and down through the soil, acting 

 upon the silica, lime, phosphoric acid and potash, render- 

 ing then soluble, and supplying them directly to the feed- 

 ers of the plants.*' 



"Air is indispensable to the soil, to prepare food for 

 plants, by the chemical action of oxygen and carbonic 

 acid." Sc. AGR. 



In order to secure a free circulation of air in the soil, 

 thorough drainage and deep tillage are necessary. 



"The advantages of drainage are not confined to land 

 which is absolutely wet, but its beneficial effects will be 

 experienced in all those soils in which water can remain 

 stagnant, at any time, at a less depth than three or four 

 feet beneath the surface. Like shallow tillage, want of 

 drainage compels the roots of plants to remain near the 

 surface of the ground, where they are not only exposed to 

 all the vicissitudes of weather, but are also compelled to 

 seek their nourishment within very narrow limits. Drain- 

 age, therefore, loosens and aerates the soil and subsoil, in 

 such a. manner that the roots of plants are enabled to p.en- 

 etrate deeper, to strata which are rarely, or never, suffi- 

 ciently affected by drouth, to allow injury to vegetation." 

 (HILGARD Agl. Kept. Miss.) 



To sum up, the effects of drainage are : 



The soil is made porous and productive, by being warm- 

 er, and by having a greater depth for the roots. 



The lands dry faster after a rain, and yet resist drouth 

 better. 



Fertilizers act better. 



It prevents washing away of the soil, and, consequently, 

 of fertilizers. 



It prevents miasma and malaria by carrying off stagnant 

 water. 



It not only improves the mechanical condition of the 

 soil, but facilitates chemical action, which results in the 



