Characteristics of the Environment - Field Sampling: Principles and Practices in Environmental Analysis - page 31

Utah or the Dead Sea is formed. If rainfall is low and evaporation high then a salt flat is
formed where there is a crust of salt on the soil surface.
2.2.1. Horizonation
Soils contain horizons, which develop as a result of soil-forming factors. These factors
are time, topography, parent material, climate, and biota. The soil-forming factors cannot
be put in order of more to less important; all are interdependent and all interact to provide
the environment under which the soil is developing. During sampling activities, these
factors will be overlain, mixed, and complicated by the activities of plants, animals, and
man.
Soil does not develop directly from rock but rather from decomposed rock. The type of
soil developed and the time necessary for its development will thus be strongly
influenced by the parent material or decomposed rock from which it is developing. If the
material is rock ground up during movement by air, water, or ice, the soil will develop
faster than if it is developing from slowly decomposing rock.
It takes a long time for a fully developed soil to be formed (see Figure 2.4), perhaps as
long as 1000 years. Thus, time is a critical factor in soil formation. In order for time to
work the material must be remain in the same place. The tendency to remain or move will
depend on the topography of the area, so this is another important factor in soil
formation. Soil developing on a hillside will be subjected to more erosion than a soil on a
flat plane. A depressional area will have more water and will collect decomposed
materials from which its soil is forming. The soil formation will thus tend to be more
rapid under these conditions.
Climate is another critical factor during the development of a soil. Salts may be
completely leached from soil, while other materials are moved into lower horizons by
percolation water. For this reason rainfall is extremely important, and soil will tend to
develop faster where there is more rainfall. However, along with rainfall, the average
temperature also will be important. The rate of chemical and biological reactions in soil
increases twofold for each 10°C increase in temperature. For this reason the climate
under which a soil develops has a strong influence on both its physical and chemical
characteristics.
Finally, both the vegetation adapted to the climate and the animals present have a
pronounced influence on soil development. Plant roots produce acids and increase the
carbon dioxide content in the soil atmosphere. Different soils develop under trees than
under grass vegetation because of their different growth and rooting habits. Animals also
play a role in soil-forming processes. Worms, termites, moles, groundhogs, and many
other animals move soil from lower horizons to the surface. In addition, they leave large
holes that water can flow into and through.