THE FORMS OF SOIL- WATER 



1G9 



through the connecting film until the pull at A and that at B 

 become the same. Such an adjustment might go on over a 

 large number of films, and if one end of the column was ex- 

 posed to an evaporation of just the correct rate and the other 

 end was in contact with plenty of moisture, large quantities 

 of water would be moved by capillarity. 



This capillary movement may go on in any direction in the 

 soil, since it is largely independent of gravity; yet under 

 natural field conditions the adjustment tends to take place 

 very largely in a vertical direction, due to evaporation and 

 absorption by plants. When a soil is exposed to evaporation, 

 the surface films are thinned and water moves upward to 

 adjust the tension. This explains why such large quantities 

 of soil-water may be lost so rapidly from an exposed soil. 

 Capillary adjustment may go on downward, also, as is the 

 case after a shower. Here the rapidity of the adjustment is 

 aided by gravity and movement of the water of percolation. 



The capillary adjustment in a soil tends to take place 

 whether or not the soil column is in contact with free water. 

 If no gravity water is present, the adjustment is merely from 

 a moist soil to a drier one. In studying the rate and height 

 of capillary movement of water in any soil, especially in the 



yield data regarding rate of movement, — a factor of vital importance 

 to plant growth. 



Lynde and Dnpr6, in their results, confirm the statements already made 

 regarding the relation of texture to capillary power: 



Soil 



Medium sand. . . 



Fine sand 



Very fine sand 



Silt 



Clay 



DiAMETEE OF 



Grains in 

 Millimeters 



.50 - .25 

 .25 - .10 

 .10 - .05 

 .05 - .005 

 .005 



Lift of Water 

 Column, in Feet 



^8 



1.78 



4.05 



9,99 



26.80 



Lynde, C. J., and Dupre, H. A,, On a New Method of Measuring 

 the Capillary Lift in Soils; Jour. Amer. Soc. Agron., Vol. 6, Ko. 2, 

 pp. 107-116, 1913, 



