THE PROPERTIES OF SOILS 



A strip of cloth having one end dipped in water draws the water 

 up into the fine openings between the threads until it becomes 

 moist several inches above the level 

 of the water. These illustrations rep- 

 resent the manner in which the capil- 

 lary water of the soil is held and drawn 

 up through the fine openings exist- 

 ing between the soil grains (Fig. 33). 



70. The effect of soil texture upon 

 the amount of water retained. The 

 finer the soil particle, the greater the 

 total amount of exposed surface over 

 which the thin films of water may be 

 spread ; also the finer the soil, the 

 more fine openings there will be in 

 which water will be retained by capil- 

 lary action. Consequently fine soils 

 retain more water for plant use than 

 coarse soils. For these reasons fine 

 soils are often spoken of as moist 

 soils, while coarse soils are spoken of 

 as dry soils. However, a soil may be 

 so fine that much of the water fall- 

 ing as rain will run off, and the rate 

 of movement of water through it is 

 too slow to supply the needs of the 

 plants. Sandy soils, on the other 

 hand, while incapable of holding as 

 much water as those of finer texture, 

 absorb water and give it up to grow- 

 ing plants so readily and completely 

 that they are the most productive 

 soils in regions of limited rainfall. 



71. How water travels in the soil. During heavy rains 

 water passes rapidly downward into the soil. The water which 

 drains downward by gravity is called gravitational, or: free, water. 



FIG. 33. The rise of water in 

 the soil 



A glass tube filled with soil is 

 placed with one end in a dish of 

 water. The water rises slowly in 

 the soil, the moist soil appearing 

 darker than the dry soil 



