3
Soil Taxonomic Systems Used in the Great
Lakes Coastal Zone
3.1
Soil Horizons
Genetic soil horizons are important role in describing and
classifying soils. A soil horizon is a layer that lies more or
less parallel to the land surface that results from the interplay
of the soil-forming factors described in the previous chapter.
Table 3.1 lists the master horizons and suffix symbols that
are used for soils in the Great Lakes region in the US and
Canadian soil classification systems. These symbols will be
referred to in the text.
3.2
Approaches to Soil Classification
During the first half of the twentieth century, soil classification systems were based on poorly understood
soil-forming processes, including soil classification systems
used in the USA from 1927 until the late 1950s (Marbut
1927; Baldwin et al. 1938). However, starting with the
‘‘Seventh Approximation’’ (Soil Survey Staff 1960) and
culminating with Soil Taxonomy (ST) (Soil Survey Staff
1975, 1999), soils in the USA and in countries adopting ST
were classified with quantitative properties, particularly
morphological properties, delineated as diagnostic epipedons
and horizons. Soil-forming processes were de-emphasized
and kept in the background. A similar approach was used by
the FAO-UNESCO (1974) and in the World Reference Base
(WRB) for Soil Resources (FAO 1998).
The movement away from an emphasis on soil processes
was predicated on the assumption that soil properties are
more readily quantifiable than soil processes and that soil
processes occur simultaneously in a given soil, reinforcing
or contradicting one another (Simonson 1959). It was also
assumed that polygenesis likely has occurred in most, if not
all soils, making genetic interpretations difficult. As
soil-forming factors change, soil-forming processes change,
resulting in a change in soil taxa. An additional criticism of
soil classification systems based on soil processes is that they
often contain insufficient taxa to satisfactorily delineate
global soils.
One of the creators of ST, Smith (1983, p. 43) emphasized: “The genesis per se, cannot be used to define soil taxa
and meet this objective. The processes that go on can rarely
be observed or measured. Nevertheless, the genesis of soils
is extremely important both to the taxonomy of soils and to
the mapping in the field. Genesis is important to the classification partly because it produces the observable or measureable differences that can be used as differentiae. Genesis
does not appear in the definitions of the taxa but lies behind
them.”
3.3
Soil Taxonomy
3.3.1 Hierarchical Levels
Soil Taxonomy (the full title is Soil Taxonomy: a Basic
System of Soil Classification for Making and Interpreting
Soil Surveys) was initially published in 1975 and revised in
1999. The system is hierarchical and includes six levels from
broadest to narrowest: order, suborder, great group, subgroup, family, and series (Table 3.2). The system is based on
diagnostic surface (epipedons) and subsurface horizons.
3.3.2 Diagnostic Horizons
Eight epipedons are defined on the basis of color, organic
carbon concentration, thickness, base saturation, presence of
andic properties, and evidence for human disturbance. In the
Great Lakes region, five of the epipedons are present,
including the ochric (thin or light colored and low organic
C), mollic (mineral enriched with organic C > 18 cm thick,
dark-colored, abundant organic C and bases), histic (organic > 30 cm thick), umbric (same as mollic except with
low base saturation), and folistic (organic horizon > 15 cm
thick that is saturated for less than 30 days). The ochric
© Springer Nature Switzerland AG 2021
J. G. Bockheim, Soils of the Laurentian Great Lakes, USA and Canada,
https://doi.org/10.1007/978-3-030-52425-8_3
35
Soil Taxonomic Systems Used in the Great
Lakes Coastal Zone
3.1
Soil Horizons
Genetic soil horizons are important role in describing and
classifying soils. A soil horizon is a layer that lies more or
less parallel to the land surface that results from the interplay
of the soil-forming factors described in the previous chapter.
Table 3.1 lists the master horizons and suffix symbols that
are used for soils in the Great Lakes region in the US and
Canadian soil classification systems. These symbols will be
referred to in the text.
3.2
Approaches to Soil Classification
During the first half of the twentieth century, soil classification systems were based on poorly understood
soil-forming processes, including soil classification systems
used in the USA from 1927 until the late 1950s (Marbut
1927; Baldwin et al. 1938). However, starting with the
‘‘Seventh Approximation’’ (Soil Survey Staff 1960) and
culminating with Soil Taxonomy (ST) (Soil Survey Staff
1975, 1999), soils in the USA and in countries adopting ST
were classified with quantitative properties, particularly
morphological properties, delineated as diagnostic epipedons
and horizons. Soil-forming processes were de-emphasized
and kept in the background. A similar approach was used by
the FAO-UNESCO (1974) and in the World Reference Base
(WRB) for Soil Resources (FAO 1998).
The movement away from an emphasis on soil processes
was predicated on the assumption that soil properties are
more readily quantifiable than soil processes and that soil
processes occur simultaneously in a given soil, reinforcing
or contradicting one another (Simonson 1959). It was also
assumed that polygenesis likely has occurred in most, if not
all soils, making genetic interpretations difficult. As
soil-forming factors change, soil-forming processes change,
resulting in a change in soil taxa. An additional criticism of
soil classification systems based on soil processes is that they
often contain insufficient taxa to satisfactorily delineate
global soils.
One of the creators of ST, Smith (1983, p. 43) emphasized: “The genesis per se, cannot be used to define soil taxa
and meet this objective. The processes that go on can rarely
be observed or measured. Nevertheless, the genesis of soils
is extremely important both to the taxonomy of soils and to
the mapping in the field. Genesis is important to the classification partly because it produces the observable or measureable differences that can be used as differentiae. Genesis
does not appear in the definitions of the taxa but lies behind
them.”
3.3
Soil Taxonomy
3.3.1 Hierarchical Levels
Soil Taxonomy (the full title is Soil Taxonomy: a Basic
System of Soil Classification for Making and Interpreting
Soil Surveys) was initially published in 1975 and revised in
1999. The system is hierarchical and includes six levels from
broadest to narrowest: order, suborder, great group, subgroup, family, and series (Table 3.2). The system is based on
diagnostic surface (epipedons) and subsurface horizons.
3.3.2 Diagnostic Horizons
Eight epipedons are defined on the basis of color, organic
carbon concentration, thickness, base saturation, presence of
andic properties, and evidence for human disturbance. In the
Great Lakes region, five of the epipedons are present,
including the ochric (thin or light colored and low organic
C), mollic (mineral enriched with organic C > 18 cm thick,
dark-colored, abundant organic C and bases), histic (organic > 30 cm thick), umbric (same as mollic except with
low base saturation), and folistic (organic horizon > 15 cm
thick that is saturated for less than 30 days). The ochric
© Springer Nature Switzerland AG 2021
J. G. Bockheim, Soils of the Laurentian Great Lakes, USA and Canada,
https://doi.org/10.1007/978-3-030-52425-8_3
35