CAPILLARY WATER 203 



(c) Moisture equivalent =( Moisture holding capacity 21) X .635 

 (b) Moisture equivalent = Hygroscopic coi ; Hicient X 2.71 



(a) Moisture equivalent = Wilting coi'-fficient X 1.84 



(d) Moisture equivalent = 0.02 sand -f 0.22 silt + 1.05 clay. 



Movement. The movement of capillary water may take place 

 in any direction, but with slightly greater facility downward than 

 upward or sidewise, because of the aid of gravity. The rate and 

 height of movement depend upon several factors. 



1. The Thickness of the Film. One of the most important 

 factors in capillary movement is the thickness of the film of water 

 on the soil particle. As a general rule, the greater the difference 

 between the moisture content of adjacent soil masses, or the greater 

 the difference in the thickness of films, the stronger will be the pull 

 and the more rapid will be the movement. This is very well shown 

 in soils adjacent to free or gravitational water. The distribution 

 near the free water takes place rapidly through capillary passages, 

 while at some distance the movement is by means of thin films and 

 slow surface distribution. If this movement is upward, it is re- 

 tarded by gravity, but if downward, as after a rain, the movement 

 becomes somewhat rapid, especially if the films are quite thick. 



To determine how rapidly or slowly water moves from a moist 

 soil into a dry one, bury a dry clod two or three inches in diameter, 

 in soil with medium moisture content, and examine every three or 

 four days. The movement is very slow. Two or three weeks will 

 be required for the clod to become moistened. It is without doubt 

 true that the roots of plants go after the moisture rather than wait 

 for the moisture to move to them by capillarity. This fact controls 

 to a large extent the root development of plants. It must be remem- 

 bered that very little capillary water used by plants is drawn from 

 the water table of the soil, which is usually many feet beneath the 

 surface. Plants sometimes wilt when the free water is not more 

 than three or four feet beneath the surface, which means that the 

 moisture rising by capillarity is not sullieicnt for the use of the 

 plant. The fact that moisture moves so slowly through a dry soil 

 is what makes dust mulches so effective. 



In order to show the rate of movement of water through the 

 soil, after the dry summer of ISK'.t, King, of Wisconsin, collected 

 samples of soil to a depth of five feet, and a portion of the dry area 

 was effectually protected from rain and snow and left in this con- 

 dition until April the following year. Samples were then collected 



