SOIL WATER, DRAINAGE, AND IRRIGATION 209 



bored in such a location as to strike the water in the lower 

 parts of the layer, so that the pressure from the higher portions 

 of the same layer will cause the water to rise to the surface. 

 Sometimes this pressure is sufficient to cause the water to rise 

 many feet into the air. 



231. Artificial drainage of soil water. Much of the surplus 

 water of the soil will naturally drain downward to the water 

 table, but agricultural plants grow better when by artificial 

 drainage as much water is removed as will readily flow into 

 underground drains. The advantages are probably at least 

 fourfold : surplus water is removed, the soil is better aerated, 

 the soil becomes warm earlier in the season, and injurious 



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FIG. 101. The water table 



Diagram to represent the water tahle in a series of hills and valleys. Line A rep< 



resents the position of the water tahle in wet weather; line B, in dry weather; 



S, springs ; W, wells 



soil substances excreted from plant roots may be removed 

 as surplus water passes downward. If you will plant two 

 jars of seedlings, one in a well-drained glass jar and the 

 other in a jar without drainage, and give them the same 

 amount of water, you will see some of the advantages of 

 soil drainage. 



232. Irrigation. In many parts of the country the annual 

 rainfall is too small or is confined to so short a period of the 

 year that there is not sufficient water in the soil to enable 

 plants to grow. There are many hundred thousand acres of 

 soil the composition of which is favorable to the growth of 

 plants, but which are deficient in water. Various devices are 

 used for irrigating some of these lands, with varying degrees 



