Agriculture Reference
In-Depth Information
developed by Canada, France, the Former Soviet Union, China, Australia, and
other countries. Each recognizes a different number of major soil groups or
soil orders.
Two basic concepts are used in developing the naming of different soils. First
is the idea that a soil's characteristics will determine which group it falls into
and its name.Another idea is that soils will be related to a reference soil. In both
cases the natural soil horizons are used in the soil description. In Soil Taxon-
omy horizons used for naming the soil are called
diagnostic horizons
. In the ref-
erence soils the horizons are called
reference horizons
.The general concepts are
similar in all systems, and so are many names for soil characteristics. The names
are often descriptive in that they give an idea of the characteristic of the soil.
In the FAO soil system and Soil Taxonomy several soils have the same or
similar names or names that can easily be seen as being related to each other.
Examples would be Histosols and Vertisols, which carry the same name in both
systems. Andosols and Andisols only differ by only one letter. Ferralsols and
Oxisols should be understood as being similar if one knows a little about
highly weathered soils. If one is working on an international scale or wishes
to work globally, it is important to know that there are different ways of
naming soils and that familiarity with the characteristics of various soil types
is necessary. This is particularly important if one is developing a soil testing
method or instrumental method, which might be either inadvertently or inten-
tionally used on an international scale.
1.5.
THE LANDSCAPE
In a landscape, the scientist differentiates one soil from another by the soils'
physical, including horizonation, and chemical characteristics. The smallest
unit that can be considered a soil, called a
pedon
, has an area of 1-10 m
2
and
is normally 1.5-2 m deep. If an area contains contiguous pedons of similar
characteristics, it is said to be a
polypedon
(multipedon) region.
In the USDA Soil Taxonomy and in field reports of soils the description
given is that of a pedon—considered the “typical” pedon. In the first case the
field description is that of a pedon, and when mapping soils the soil mapping
unit strives to capture the distribution of similar polypedons. A soil mapping
unit applied to the field may contain “inclusions” of dissimilar ploypedons.
Both the Soil Taxonomy and the soil mapping unit nomenclature contain the
terminology likely to be associated with soil samples that the soil chemist,
environmental analyst, or instrument procedure developer will encounter.
Knowing where the soil comes from, its Soil Taxonomy designation, and field
description give the soil researcher and analyst a great deal of information
about the chemical characteristics of the soil. In addition, reporting the soil
name and its analysis together provide the reader with information that is
invaluable in applying the results to that particular soil as well as other
environmental conditions.
