ABSTRACT
Soils are not homogeneous. They are heterogeneous on any scale. Soils generally differ laterally over distances of meters, vertically over distances of centimeters or millimeters, and microscopically over shorter distances. Most soils grade laterally in gradual transitions to other kinds of soils. Small units of 1 to 10 m2 that are relatively uniform laterally are chosen to represent soils. These units have been called pedons, as shown in Figure 1.1. Within pedons most of the differences are vertical. Different layers are called horizons, because they are generally parallel to the ground surface that represents the horizon between land and sky.
