CHAPTER III 

 SOILS 



25. Classification of soils. The Bureau of Soils of the 

 United States Department of Agriculture has established 

 a system of soil classification which should be familiar 

 to every student of vegetable gardening. 



26. Soil type. The unit of classification is known as 

 a type. Soil Survey Field Book, 1906, p. 16: "In the 

 determination of a type of soil there are many factors to 

 be considered. Among the most important are the tex- 

 ture, which deals with the size of the particles ; the 

 structure, which deals with the arrangement ; the or- 

 ganic matter-content, origin, color, depth, drainage, 

 topography, native vegetation and natural productive- 

 ness. This classification is based primarily upon the 

 physical properties, but all factors that influence the rela- 

 tion of soils to crops, so far as their influence can be 

 determined, are taken into consideration." 



27. Soil class. Ibid., p. 16: "Soil types which consti- 

 tute the units of soil classification, may be grouped in 

 different ways. As soils are made up of particles of dif- 

 ferent sizes, they may be grouped according to the rela- 

 tive proportions of the particles of different sizes which 

 they contain. This grouping is known as the soil class 

 and is based on texture. By means of mechanical analy- 

 ses the particles less than two millimeters in diameter 

 are separated into seven grades, and the various per- 

 centage relationships of the different grades determine 

 the class of soil ; that is, they determine whether it is 

 sand, sandy loam, loam, clay or some intermediate class. 

 In addition to the fine earth, of which a mechanical 

 analysis is made, many soils contain larger particles, 



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