MEANINGS OF TEXTURE AND STRUCTURE COMPARED 13 



come to live in the soil by the millions because of the presence of 

 organic matter which, because of the energy or food stored up in it, 

 is the source of most of their sustenance and their energy. Some of 

 these organisms are a detriment to soils, while others, because of 

 fundamental changes they bring about, are of the greatest im- 

 portance in crop production. 



(c) Air Soil as a medium for plant growth must contain air. 



(d) Salts in greater or less amounts in dry climates much. 



SOIL CLASSIFICATION 



Since the building materials of soils are largely mineral 

 particles which remain more or less the same in size and amounts 

 in any particular soil, we are afforded a basis whereby soils may 

 be classified. 



Crummy structure Compact structure Sandy structure 



FIG. 6. Diagrams illustrating soil structures. 



Soil Texture a Basis for Classification. The most convenient 

 and general scheme for soil classification is based on the amounts 

 of sand, silt and clay soils contain or in other words, on the basis 

 of " texture. " 



What Soil Texture Means. Soil texture may be defined as a 

 quality denoting comparative coarseness or fineness of soils as is 

 determined by the relative abundance of sand, silt and clay con- 

 tained in them. For example, a soil having course sand predomi- 

 nating is a course textured soil, whereas one having much clay is re- 

 garded as fine textured. 



Meanings of Texture and Structure Compared. Texture 

 should not be confused with soil "structure" which means the 

 arrangement of the soil grains (Fig. 6), or which describes the rela- 

 tion of the soil particles to each other. It is important to remember 

 that the soil components do not form a mere casual mixture in 

 which every particle remains separate from every other particle. 

 With the exception of sands, the soil components, because of the 



