THK SOIL AND ITS IMPROVEMENT 



b. Silt is a term used to define soil particles next larger 

 than clay. A silt particle is so small that it would re- 

 quire 500 of the largest ones placed side by side to extend 

 one inch. A silt soil is slightly lighter and more porous 

 than a clay soil. Like clay it retains moisture and fer- 

 tility very well, and is, therefore, well adapted for corn and 

 grain, especially during dry seasons. Both clay and silt if 

 properly worked will become granular or open ; that is, 



many of these tiny par- 

 ticles unite into little 

 masses or granules and 

 thus resemble sand. 



c. Sand. Soil made 

 up of particles larger 

 than those that form silt 

 is called sand. The 

 United States Bureau 

 of Soils recognizes dif- 

 ferent grades of sand 

 based on the size of tin- 

 particles. Sand parti- 

 cles run from one 

 twenty -fifth to one two- 

 hundredth of an inch in diameter. Soils containing con- 

 siderable sand are called light, because they are easily 

 worked. A cubic foot of dry sand, however, really weighs 

 more than a cubic foot of dry clay. Pure sand is mostly 

 quartz (a mineral closely related to glass), and it contains 

 little food ready for plant use. 



d. Gravel. Tiny bits of rock between one twelfth 

 and one twenty-fifth of an inch in size form gravel. 

 Gravel differs still more from clay than sand does, and it 

 dries out even faster than sand. 



e. The term stone in agriculture refers to all rock 



SAND. 

 Seen under the microscope. 



