722 SOILS: PROPERTIES AND MANAGEMENT 



619. Texture — the soil class. — Of all the properties 



of the soil, the one which is most apparent and which 

 exerts the most direct influence on the plant is the tex- 

 ture, or fineness of division, of the soil particles. Is it a 

 clay, a silt, a sand, a gravel, or some combination of these ? 

 Is it stony, or is it free from stone? The texture is the 

 first property made use of in classifying soil. This divi- 

 sion based on texture is called the soil class. It is a purely 

 physical division, and does not recognize any chemical 

 or other differences in the soil except as such differences 

 may occur between coarse and fine materials. 



620. Special properties — the soil series. — Soils of 

 different texture may be alike in other properties. They 

 may be all red, all black, or all yellow. They may be 

 well drained or poorly drained. Such a group of soils of 

 different texture but alike in all other properties consti- 

 tutes a soil series. The properties by which the soil 

 series is recognized are (1) color, which is predominant 

 in the separation, (2) content of organic matter, (3) natural 

 drainage, (4) content of lime carbonate, (5) ultimate 

 chemical composition, and (6) arrangement of the soil in 

 the section. Any one or a combination of these properties 

 may identify an area of soils. Such an area would con- 

 stitute a soil series. These properties permit the recog- 

 nition of chemical differences quite as much as physical 

 differences of the soil in mass. 



If it were possible clearly to identify all the properties 

 that may be recognized in the series and class divisions, 

 there would be no need of employing other factors in the 

 classification. Such a clear identification, however, is 

 only partially possible, and is further limited by the 

 conditions under which the soil survey must be carried 

 out in the field. Many of these properties are of such 



