CHAPTER I 



PHYSICAL PROPERTIES OF SOILS 



1. Soil. Soil is that portion of the earth's crust 

 in which plants may grow. It is composed of pulver- 

 ized and disintegrated rock mixed with animal and 

 vegetable matter. The rock particles are of different 

 kinds and sizes, and are in various stages of decomposi- 

 tion. If two soils are produced from the same kind of 

 rock and differ only in the size of the particles, the 

 difference is merely a physical one. If, however, one 

 soil is formed largely from sandstone, while the other is 

 formed from granite, and the soil particles are not the 

 same in size, the difference is both physical and chemi- 

 cal. Soils are derived from different kinds of rock 

 fragments, which are composed of minerals having 

 a different combination of elements and different per- 

 centage composition, and hence it is they differ both 

 physically and chemically. It is difficult to consider 

 the physical properties without also considering the 

 chemical properties. The chemical and physical prop- 

 erties, together, determine largely the agricultural value 

 of a soil. 



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