WATER THROUGH DIFFERENT SOILS 45 



Discussion: After a rain, when the capillary or film 

 capacity of the soil has been reached, the free or gravi- 

 tational water percolates down to the subsoil and runs 

 away. The rate at which this free water gets out of the 

 zone of the roots is called the rate of percolation. This 

 rate depends upon the fineness of the particles, the degree 

 of granulation, and the content of organic matter. In 

 soils in which the particles are comparatively fine and the 

 spaces between the particles correspondingly small, the 

 percolation is slow. When a fine soil is well granulated, 

 the larger spaces between the granules permit a more rapid 

 flow. This is desirable, since, to have the soil saturated 

 long is injurious to crops. On the other hand in some 

 sandy soils percolation may he so rapid as to cause leach- 

 ing, i.e., carr3dng away of the plant nutrients. The addi- 

 tion of organic matter tends to prevent leaching. 



