THE TEXTURE OF THE SOIL 39 



a greater feeding -surf ace to roots, because the 

 particles of earth are very small (52). Boots 

 feed on the surfaces of hard particles of earth, 

 and the feeding -area is therefore increased in 

 proportion to the increase in the surface area 

 of the particles. Dividing a cube into two 

 equal parts increases its surface area by one- 

 third. (Dividing a cube adds two sides or 

 surfaces.) Fining the soil may therefore be 

 equivalent to fertilizing it, so far as plant - 

 growth is concerned. 



3. How Good Structure is Secured 



54. The size of the soil particles, determin- 

 ing the texture of the soil, cannot be modified to 

 any appreciable extent by ordinary farm practices. 

 Tillage has little effect in changing the size of 

 the ultimate particles. 



55. The arrangement of the particles, which 

 determines the structure, can be greatly changed 

 by farm practice. If the structure is lumpy and 

 open, the soil needs pulverization; if it is com- 

 pact and hard, it needs loosening up. Very 

 loose and leachy soils are usually improved if 

 the particles, particularly in the under soil, are 

 brought together and compacted. 



56. The size of the granules (or aggregations 

 of particles) of soils is modified by three general 



