CHAPTER III 
SOILS 
25. Classification of soils. — The Bureau of Soils of the 
ijnited States Department of Agriculture has established 
;j 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 
Ihey 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, 
17 
