THE IMPROVEMENT OF SOILS. 43 



clay subsoils, drainage usually results in great improve- 

 ment and profit to the owner. 



Methods of Drainage. — The eiBficiency of drains de- 

 pends upon the free passage of water through them. They 

 should always lead to the lowest portion of the field ; if 

 the land is level, they must be gradually sloped — one 

 foot in five hundred will furnish sufficient grade for the 

 flow of water. On a slope, the drains may be laid at a 

 uniform depth from the surface ; the main drain should 

 always occupy the lowest part of the field. 



The depth of drains and their distance from each other 

 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 to one 

 another. The mouth of the drain should be well pro- 

 tected, and kept free from all obstructions. 



Irrigation. — When lands contain too little water irri- 

 gation is frequently resorted to, though the best results 

 from irrigation are attained on well-drained land. Irri- 

 gation not only softens the land, thus making it more 

 permeable for the roots of plants, but it is effective in 

 dissolving the dormant constituents of soils. Large tracts 

 of now barren land in the United States only require water 

 to make them fruitful. 



The advantages of irrigation are, perhaps, most con- 

 spicuous in the States of Colorado and California. In 

 portions of the Eastern States crops are frequently ruined 

 by a lack of water at the right time ; the irrigation of 

 these areas is only a question of time. 



Claying and Sanding. — Further imperfections in 

 the physical character of natural soils are also common. 



