THE SOIL AND SOIL FORMATION 



77 





attracting power of the surfaces of the uppermost soil 

 particles is satisfied, and they allow the layer of particles 

 next beneath to draw away the surplus. In this way a 

 very gentle rain is taken hold of by the soil particles, 

 and is slowly moved or drawn downward by what is 

 termed the capillary force of the soil. The soil thus 



takes the moisture downward 

 in much the same manner as a 

 sponge, when placed with its 

 lower portion in a small 

 amount of water in a saucer, 

 absorbs the water upward into 

 its own body, though very 

 much more slowly. Gravita- 

 fc ? tion, of course, aids the down- 

 L b? e e n SfflTES ward capillary movement, and 

 slightly retards its upward 

 movement, as in the sponge. When filled, or saturated, to 

 its full capacity with capillary water, the 100 pounds of 

 original dried, water-free soil, with its added water, 

 weighs, perhaps, 145 pounds. In Figure 22 the soil is 

 shown to have its capillary 

 powers saturated in the upper 

 half. 



Crops could not thrive in 

 soil as dry as that represented 

 in Figure 20 or even that in 

 Figure 21, with only hygro- 

 scopic water present, but plants 

 which thrive in our arable 

 lands have, through the cen- pot - 

 turies of their development, become accustomed to 

 soils with their capillary forces only partly satisfied. 

 Soil with its capillary forces fully satisfied with 45 

 pounds of water to the hundred pounds of soil, would 

 be so wet that corn, and most other crops, would not 



Figure 23. Capillary powers of the 

 soil satisfied to the bottom of the 



