48 THE PRINCIPLES OF AGRICULTURE 



other one cause. In certain sections of the conn- 

 try irrigation is successfully employed; but 

 most farmers must depend on the rainfall as the 

 chief source for the supply of moisture. 



2. Hoiv Water Is Held in the Soil 



64. The water in the soil may be in one of 

 three forms, — free, capillaiy, or hygroscopic 

 water. 



65. The free water of the soil is that which 

 flows under the influence of gravity. It is this 

 water which is removed in part by drains, and 

 which is the source of supply for wells and 

 springs. It is not utilized directly by cultivated 

 plants, but it is valuable when removed a 

 proper distance from the surface, because it 

 serves as a reservoir from which moisture may 

 be drawn by capillary action. 



66. Capillary water is that which is held by 

 adhesion to the soil particles, or in the inter- 

 stices or openings between the particles. It is 

 not controlled or influenced by gravity, but 

 passes from one part of the soil to another, 

 tending to keep the soil in equilibrium (or in 

 uniform condition) so far as its moisture is 

 concerned. The capillary water is the direct 

 supply for plants, and it is this which should 

 be naost carefully provided for and saved. 



