THE MOISTURE IN THE SOIL 55 



have already seen (57, 75-78) that draining in- 

 creases the depth of the soil ; so does deep plow- 

 ing. Capillarity is increased by finely dividing 

 or pulverizing the soil. 



80. Increasing the capillarity increases the 

 moisture -holding capacity of soils in two ways : 

 it enables the soil to actually hold more mois- 

 ture per square inch ; it enables it to draw 

 up moisture from the free water of the lower 

 subsoil (65). 



81. By the action of capillary attraction, 

 moisture moves from one layer of soil to another 

 (66), usually from the lower to the upper, to 

 supply the place of that which has been used 

 by plants, or which has been lost by evapora- 

 tion. The rapidity of movement and the force 

 with which it is held depend upon various 

 conditions. A soil in which the particles are 

 somewhat large, as in sandy or gravelly soils, 

 may, if well compacted, show considerable ra- 

 pidity of movement, but weak power to retain 

 moisture. The finer the division of the soil 

 particles the greater is the surface presented. 

 In finely divided clay soils, the movement of 

 capillary water is slow but the retaining power 

 is great. Occasionally it happens that the par- 

 ticles are so fine that the spaces disappear, and 

 there is produced a condition through which 

 moisture and air cannot pass. This state of 



