KINDS OF SOILS


 Soils are different in many ways, the most outstanding of
which are variations in color such as gray, brown, red, and black:
variation in size of particles such as gravel, sand, silt, and clay: (1)
variation in topography such as level, hills, or mountains: varia-
tions in parent material such as limerock, sandstone, clay, granite,
marble, and others: also variations in moisture, whether wet
or dry. One or more of these variations may be observed in
any community and is reflected by the differences in native
vegetation and crop production. In fact, these variations ac-
count for the wide variety of plant life which we see about us.

 The average person may recognize that soils differ in their
ability to grow plants, but he seldom understands how or why.
Close examination shows that soils are made up of many small
particles which vary in size and color. Sand particles vary
from about the size of a pin head to fine powder, while clay
particles cannot be seen with a microscope. Particles as large
as sorghum seed and larger are called gravel, while those in-
termediate between sand and clay is silt, which has a floury
feel. When soil is rubbed between the fingers quite different
characteristics are noted in different soils. Sands have a gritty
feel between the fingers, while clay particles are very fine and
smooth, with a sticky and plastic feel when wet. Although
all soils contain some sand, silt, and clay, the different soil
grades or classes commonly referred to as sands, loams, and
clays, merely contain different proportions of these ingredients.
Each of these class names has subdivisions such as coarse sand
and fine sand, sandy loam, silt loam and clay loam. Soils with
eighty per cent or more of the sand ingredient belongs to the
sand class. If a soil contains over fifty per cent of the clay
ingredient it is a clay soil while the loams contain from twenty
to fifty per cent clay and silt ingredients. Further examination
of a soil shows that the surface is usually darker than the sub-
soil which often exhibits distinct layers or strata. These may
be seen along roadside banks or ditches. (These layers are
illustrated for two Florida soils in Plate I.) The nature of
(1). Gravel-1 to 2 mm. in diameter. Silt-.05 to .005 mm. in diameter
 Sand-.05 to 1 mm. in diameter. Clay-below .005 mm. in diameter.