Types of Soils
If we were to talk to soil scientists, you would learn that there are thousands of types of soil.
Soil scientists study each of the many different characteristics of each soil and put them into
very specific groups and have many different names for soils. Let’s consider a much simpler
model that considers just three types of soil. This will help you to understand some of the
basic ideas about how the particular climate of an area produces a certain type of soil, but
there are many exceptions to what we will learn right now.
Let’s consider the type of soil that would form in a region of the world where there are forests
of trees that lose their leaves each winter, calleddeciduous trees. In order for trees to grow
here, there needs to be lots of rain, at least 65 cm of rainfall per year. Wherever there are
trees, there is enough rain to help them grow! The type of soil that forms in a forested area
is called apedalferand this type of soil is common in many areas of the temperate, eastern
part of the United States (Figure9.10). The word pedalfer comes from some of the elements
that are commonly found in the soil. The element aluminum has the chemical symbol Al
and the element iron has the chemical symbol Fe. These two symbols are combined ‘-al’ and
‘-fe’ to make the word ped –al–fe r. This type of soil is usually a very fertile, dark brown or
black soil. It is rich in aluminum clays and iron oxides. Because it rains often in this type of
climate, most of the soluble minerals dissolve and are carried away, leaving the less soluble
clays and iron oxides behind.
Figure 9.10: A pedalfer is the dark, fertile type of soil that will form in a forested region. ( 9 )
Another type of climate related soil, called apedocal,forms in drier temperate areas where
grasslands and brush are the usual types of vegetation (Figure9.11). It rains less than 65
cm per year in these areas, so there is less chemical weathering for these soils. With lower
amounts of rainfall, there is less water to dissolve away soluble minerals, so more soluble