The criteria and guidelines used in differentiating classes
in the family and series categories are outlined in this
chapter. However, the numerous classes are not defined,
particularly for the soil series category (see Chapter
17 for definitions of terminology).
The family is a category of the system of soil classification
in the same sense as the order, great group, and subgroup.
However, the family is not yet as widely used as the
long-established categories such as the great group and series.
The soil family, as used in The Canadian System of Soil
Classification, was developed in the 1960s and the first
version was adopted in 1968 (National Soil Survey Committee
1968). At that time, terminology and class limits developed
in the US Soil Taxonomy were partially adopted but, in some
cases, applied somewhat differently to fit the needs of the
Canadian system.
Historically, the family category was needed because the
number of soil series was too great, and the higher categories
too heterogeneous, to be used for many objectives. Therefore,
the soil family is used to define and group soil series of the
same subgroup, which are relatively uniform in their physical
and chemical composition and environmental factors. At the
subgroup level all genetic factors are adequately taken care
of. At the family level, the practical physical factors that
affect plant growth and engineering uses of soils are taken
into account. The relative weight of engineering influences
versus agronomic influences on the choice of boundaries for
family classes is about equal. For example, in the
particle-size classes, the limits of 18% clay between coarse
and fine and loamy, reflect the change from nonplastic to
plastic limit. This is considered by engineers to be an
important distinction. Similar breaks occur at the 35% and
60% clay content. On the other hand, there is an important
agricultural difference between the coarse and fine silty
and loamy classes, especially in terms of capillary rise and
available moisture-holding capacity. Basically, the family
grouping is intended to allow groupings of soils that have a
similar response to management, and to some extent, for
engineering and related uses.
Therefore, soils in a family have in common a combination of
important specific properties adequate for broad
interpretations but inadequate for quantitative
interpretations. Soil series are better suited to that
purpose. Although the series category has been used
throughout the history of soil survey in Canada, it has
evolved to an increasingly specific category. Some of the
series, which were established before the family category
was introduced, can now be divided into several families.
In that way, the family level becomes a framework (correlation
yardstick) for checking and establishing proper limits for
soil series.
Subgroups are divided into families based on certain chemical,
physical, and other properties of the soil that reflect
environmental factors. The family differentiae are uniform
throughout the nine orders of mineral soils. Another set of
differentiae is used uniformly for soils of the Organic order.
The differentiating criteria for families of mineral soils are
particle size, mineralogy, reaction and calcareousness, depth,
soil temperature, and soil moisture regime. Those for families
of Organic subgroups are characteristics of the surface tier,
reaction, soil temperature, soil moisture regime, particle size
of terric layer, and the kind and depth of limnic layer. Many
of these properties are major ones with respect to the
suitability of the soil for various uses. An Orthic Regosol
might occur in fragmental or clayey material, or material of
some intermediate particle-size class. Particle size, which
affects many uses, is not diagnostic of soil classes above the
family category. A Rego Black Chernozem soil might have a
lithic contact at 15 cm or it might occur in deep
unconsolidated material. This important difference is not
recognized taxonomically above the family level.
The diagnostic criteria (reaction, calcareousness, and depth
classes) apply to the mineral control section as defined in
Chapter 2, whereas particle-size and mineralogical classes are
defined on a more restrictive control section (see
Control section of particle-size classes and substitute
classes later in this chapter).
The term 'particle size' refers to the grain size distribution
of the whole soil including the coarse fraction (>2 mm). It
differs from texture, which refers to the fine earth (≤2 mm)
fraction only. Also, textural classes are usually assigned to
specific horizons, whereas family particle-size classes
indicate a composite particle size of a part of the control
section that may include several horizons. These particle-size
classes may be regarded as a compromise between engineering and
pedological classifications. The limit between sand and silt
is 74 µm in engineering classifications and either 50 or
20 µm in pedological classifications. The engineering
classifications are based on weight percentages of the fraction
less than 74 mm, whereas textural classes are based on the
≤2 mm fraction.
The very fine sand fraction, 0.1-0.05 mm, is split in the
engineering classifications. The particle-size classes make
much the same split but in a different manner. A fine sand
or loamy fine sand normally has an appreciable content of
very fine sand, but most of the very fine sand fraction is
coarser than 74 µm. A silty sediment, such as loess,
also has an appreciable amount of very fine sand, but most
of it is finer than 74 µm. In particle-size classes the
very fine sand is allowed to 'float.' It is assigned to sand
if the texture is fine sand, loamy fine sand, or coarser and
to silt if the texture is very fine sand, loamy very fine
sand, sandy loam, silt loam, or a finer class.
The particle-size classes defined herein permit a choice of
either 7 or 11 classes depending upon the degree of refinement
desired. The broad class 'clayey', indicating 35% clay or more
in the fine earth of defined horizons, may be subdivided into
fine-clayey (35-60% clay) and very-fine-clayey (60% or more
clay) classes
(Figure 41).
Figure 41:
Family particle-size classes triangle (left) and soil texture classes triangle (right).
Abbreviations for the texture classes are HC, heavy clay; C, clay; SiC, silty clay; SiCL, silty
clay loam; CL, clay loam; SC, sandy clay; SiL, Silt Loam; L, loam; SCL, sandy clay loam; SL,
sandy loam; Si, silt; LS, loamy sand; S, sand.
The particle-size classes for family groupings are as follows:
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(>250 mm), cobbles (75-250 mm) and gravel (>2-75 mm),
comprise 90% or more of the soil mass (by volume), with too
little fine earth (<10% by volume) to fill interstices
larger than 1 mm.
Particles >2 mm occupy 35% or more but less than 90%
(by volume), with enough fine earth to fill interstices
larger than 1 mm; the fraction ≤2 mm is that defined for
the sandy particle-size class.
Particles >2 mm occupy 35% or more but less than 90%
(by volume), with enough fine earth to fill interstices
larger than 1 mm; the fraction ≤2 mm is that defined for
the loamy particle-size class.
Particles >2 mm occupy 35% or more but less than 90%
(by volume), with enough fine earth to fill interstices
larger than 1 mm; the fraction ≤2 mm is that defined for
the clayey particle-size class.
The texture of the fine earth includes sands and loamy sands,
exclusive of loamy very fine sand and very fine sand textures;
particles >2 mm occupy less than 35% (by volume).
The texture of the fine earth includes loamy very fine sand,
very fine sand, and finer textures with less than 35% (by
weight) clay1; particles >2 mm occupy less than
35% (by volume).
- A loamy
particle size that has 15% or more (by weight) of fine
sand (0.25-0.1 mm) or coarser particles, including
fragments up to 75 mm, and has less than 18% (by weight)
clay1 in the fine earth fraction.
- A loamy
particle size that has 15% or more (by weight) of fine
sand (0.25-0.1 mm) or coarser particles, including
fragments up to 75 mm, and has 18-35% (by weight)
clay1 in the fine earth fraction.
- A loamy
particle size that has less than 15% (by weight) of fine
sand (0.25-0.1 mm) or coarser particles, including
fragments up to 75 mm, and has less than 18% (by weight)
clay1 in the fine earth fraction.
- A loamy
particle size that has less than 15% (by weight) of fine
sand (0.25-0.1 mm) or coarser particles, including
fragments up to 75 mm, and has 18-35% (by weight)
clay1 in the fine earth fraction.
The fine earth contains 35% or more (by weight)
clay1 and particles >2 mm occupy less than 35%
(by volume).
- A clayey
particle size that has 35-60% (by weight) clay1
in the fine earth fraction.
- A
clayey particle size that has 60% or more (by weight)
clay1 in the fine earth fraction.
|
|
Special terms are used for some soils in which particular
combinations of texture and mineralogy require special
emphasis. At present these include soils containing large
amounts of volcanic ash and cinders, and
thixotropic2 soils where particle-size class has
little meaning. The terms ashy and cindery apply to some
soils differentiated formerly as Andic3 subgroups
of Brunisolic soils. These terms replace both particle-size
and mineralogy family class terms.
|
At least 60% (by weight) of the whole soil consists of volcanic
ash and cinders; 35% or more (by volume) of cinders have a
diameter of >2 mm.
At least 60% (by weight) of the whole soil consists of
volcanic ash and cinders; less than 35% (by volume) has a
diameter of >2 mm.
Particles >2 mm in diameter, other than cinders, occupy
35% or more (by volume); the fine earth fraction is ashy as
defined above.
Particles >2 mm in diameter occupy less than 35% (by
volume); the fine earth fraction is thixotropic and the
exchange complex is dominated by amorphous materials.
Particles >2 mm in diameter, other than cinders, occupy
35% or more (by volume); the fine earth fraction is
thixotropic as defined above.
|
In assigning particle-size classes only a segment of the
mineral control section as defined in Chapter 2 is commonly
used. Surface layers are generally excluded and Bn and Bt
horizons are given special emphasis. To apply particle-size
classes, use the weighted average particle size of a segment
of the control section as defined below. The weighted average
can usually be estimated, but in marginal cases the weighted
average percentage of one or more size fractions may need to
be calculated. This is done by summing the products of size
fraction percentage times horizon depth for the applicable
segment of the control section and dividing by the total
thickness.
If there are strongly contrasting particle sizes, as shown
in Table 1, both are used, e.g., fine-loamy over sandy.
The following guidelines indicate the segment of the control
section used for establishing soil family particle-size
classes:
- In soils having within 35 cm of the mineral soil surface
- a lithic contact, particle size is assessed in all of
the mineral material above the lithic contact;
- a permafrost layer1, particle size is assessed in all
of the mineral material between the surface and a depth
of 35 cm.
- In other soils lacking a significant Bt or Bn
horizon2, particle size is assessed in that segment
of the control section between the lower boundary of an
Ap horizon or a depth of 25 cm from the mineral soil
surface, whichever is deeper, to either
- a depth of 1 m;
- a lithic contact; or
- a depth of 25 cm below the upper boundary of a
permafrost layer, whichever is shallower.
- In other soils that have a significant Bt or Bn
horizon3 extending deeper than 25 cm from the
mineral soil surface the particle size is assessed
- in the upper 50 cm of the Bt or Bn horizons (or the
entire horizon if thinner), if there are no strongly contrasting particle-size classes in or below these horizons and there is no lithic contact at a depth of less than 50 cm from the top of the Bt or Bn horizon;
- in that segment of the control section between the
top of the Bt or Bn horizon and the 1 m depth or to
a lithic contact, which ever is shallower, if the
Bt or Bn horizon contains strongly contrasting
particle-size classes;
- in the 25-100 cm depth, if there are no strongly
contrasting classes in or below the Bt or Bn horizon,
but there is a strongly contrasting A horizon more
than 50 cm thick.
- If the base of a significant Bt or Bn horizon, or the
segment of the mineral control section in which it occurs,
is shallower than 25 cm from the mineral soil surface,
particle size is assessed from the lower boundary of that
segment below the top of the Bt or Bn or below the base
of the Ap horizon, whichever is shallower, to either
- a depth of 1 m; or
- a lithic contact, whichever is shallower.
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These classes identify major variations within the control
section that affect properties such as water movement and
retention. They emphasize features that may not have been
identified at higher taxonomic levels.
The minimum significant thickness of a strongly contrasting
layer is 15 cm. The particle-size classes in Table 1 are
strongly contrasting if the transition is less than 12 cm
thick. For ashy-skeletal and thixotropic- skeletal classes,
enter the table at clayey-skeletal.
Where three strongly contrasting layers occur within the
control section, the lowest layer and the thicker of the
overlying layers are used to establish contrasting classes.
Strongly contrasting particle-size classes are written as
follows: sandy over clayey, fragmental over sandy, etc.
Family mineralogy classes are based on the mineralogical
composition of selected particle-size fractions in that
segment of the control section used for the designation of
the particle-size class. If contrasting particle-size classes
are recognized, the mineralogy of only the upper contrasting
layer defines the family mineralogy. Like a key, soils are
placed in the first of the 13 mineralogy classes defined in
Table 2 that accommodates them, even though they may meet the
requirements of other classes. Thus a soil that has a
CaCO3 equivalent of more than 40% throughout the
control section, combined with a mixture of quartz, feldspar,
illite, and vermiculite, will be designated as a carbonatic
family mineralogy class.
In the absence of data, the placement of soils will commonly
depend on judgment. Many of the mineralogy family classes are
rare in Canada and relate to specific parent materials. Most
Canadian soils have mixed mineralogy; notable exceptions are
smectitic, clayey soils of the Interior Plains of western
Canada.
Depth classes are applicable only in mineral soils having a
lithic contact or permafrost within a depth of 1 m. In the
following classes for mineral soils, depth is measured
from the mineral soil surface to the contact:
| Extremely shallow lithic |
<20 |
| Very shallow lithic |
20-50 |
| Shallow lithic |
>50-100 |
| Extremely shallow cryic |
<20 |
| Very shallow cryic |
20-50 |
| Shallow cryic |
>50-100 |
It is assumed that the range of pH in the solum is
sufficiently well characterized in the subgroup category of
most soils and requires no special recognition at the family
level. Important differences in reaction in subgroups of
Gleysols and Gray Luvisols can be accommodated at the series
level. Family reaction classes are applicable only to the C
horizons of mineral soils. They are used in all subgroups
except where they would be redundant, as in the Chernozemic
and Solonetzic orders, Gray Brown Luvisol, Melanic Brunisol,
and Eutric Brunisol great groups, and soils of sulfurous
mineralogy family class.
Classes are based on the average pH in 0.01 M CaCl2
(2:1) of the C horizon (C, Ck, Cs, Cg) including IIC, etc.,
but excluding Csa and Cca. In the absence of a C horizon,
the horizon overlying the lithic contact, or 25 cm below the
top of a permafrost layer, is used.
| Acid |
<5.5 |
| Neutral |
5.5-7.4 |
| Alkaline |
>7.4 |
| Carbonatic |
More than 40% (by weight) carbonates
(expressed as CaCO3 equivalent) plus
gypsum, and the carbonates are >65% of the sum
of carbonates and gypsum |
Whole soil, particles ≤2 mm in
diameter, or whole soil ≤20 mm, whichever has
higher percentages of carbonates plus gypsum |
| Serpentinitic |
More than 40% (by weight) serpentine
minerals (antigorite, chrystile, fibrolite, and talc) |
Whole soil, particles ≤2 mm in diameter |
| Gypsic |
More than 40% (by weight) of
carbonates (expressed as CaCO3 equivalent)
plus gypsum, and the gypsum is >35% of the sum of
carbonates and gypsum |
Whole soil, particles ≤2 mm in
diameter, or whole soil ≤20 mm, whichever has
higher percentages of carbonates plus gypsum |
| Sulfurous |
Soils containing either iron sulfates,
commonly jarosite, if the pH after oxidation is less
than 3.5; or more than 0.75% sulfur in the form of
polysulfides if the soil contains less than three
times as much carbonate (expressed as CaCO3
equivalent) as sulfur |
Whole soil, particles ≤2 mm in
diameter |
| Micaceous |
More than 40% (by weight)1
mica |
0.02-2 mm |
| Siliceous |
More than 90% (by weight)1
of silica minerals (quartz, chalcedony, or opal) and
other extremely durable minerals that are resistant
to weathering |
0.02-2 mm |
| Mixed |
All others that have <40% (by
weight)1 of any one mineral other than
quartz or feldspars |
0.02-2 mm |
| Kaolinitic |
More than 50% (by weight) kaolinite,
tabular halloysite, dickite, and nacrite by weight
and smaller amounts of other 1:1 or nonexpanding 2:1
layer minerals or gibbsite and <10% (by weight)
smectite |
≤0.002 mm |
| Smectitic |
More than 50% (by weight) smectite
(montmorillonite or nontronite) or a mixture that
has more smectite than any other clay mineral |
≤0.002 mm |
| Illitic |
More than 50% (by weight) illite
(hydrous mica) and commonly >4% K2O |
≤0.002 mm |
| Vermiculitic |
More than 50% (by weight) vermiculite
or more vermiculite than any other clay mineral |
≤0.002 mm |
| Chloritic |
More than 50% (by weight) chlorite
or more chlorite than any other mineral |
≤0.002 mm |
| Mixed |
Other soils |
≤0.002 mm |
It is assumed that carbonate (expressed as CaCO3
equivalent) levels in the solum are sufficiently well
understood from the subgroup classification of most soils and
require no special recognition at the family level. Important
differences in carbonate content in subgroups of Gleysols and
Gray Luvisols can be accommodated at the series level.
Therefore, family calcareous classes are applicable only to
C horizons of mineral soils, the mineral horizon overlying a
lithic contact, or the mineral material that occurs 25 cm
below the top of a permafrost layer, as described under
reaction classes. They are used in all soils with Ck or Cca
horizons.
| Weakly calcareous |
1-6 |
| Strongly calcareous |
>6-40 |
| Extremely calcareous |
>40 |
The class extremely calcareous is redundant in soils with
carbonatic mineralogy.
The soil climate classes and subclasses are applicable to
all soils and the criteria used are those of the map
Soil Climates of Canada (Clayton et al. 1977). In
this system soils can be grouped according to soil temperature
classes (Table 3) and soil moisture subclasses (Table 4).
Rather than relying upon the map designations for a given
area, soil sites need to be individually assessed on the
basis of observations of local climatic and microclimatic
variations. Extrapolation from local meteorological station
data should allow for any unrepresentative site features such
as vegetation and exposure. A useful estimate of mean summer
soil temperature (MSST) can be obtained by averaging the
three mid-monthly readings of soil temperature at 50 cm taken
in July, August, and September.
Family criteria apply to the organic control section
as defined in Chapter 2.
Characteristics of the surface tier may be recognized by
using one of the following:
- Organic surface tier; fennic, silvic, sphagnic (each used
only for fibric surface tiers), mesic, humic.
- Mineral surface tier1, 15-40 cm thick; sandy,
coarse-loamy, coarse-silty, fine-loamy, fine-silty, clayey.
1 = Definitions for the mineral surface tier
classes are the same as those of the particle-size classes.
|
Reaction classes are based on the average pH in 0.01 M
CaCl2 (4:1) in some part (Euic) or all parts
(Dysic) of the organic materials in the organic control
section.
The soil climate classes and subclasses are applicable to
all soils and the criteria used are those of the map Soil
Climates of Canada (Clayton et al. 1977). In this system
soils can be grouped according to soil temperature classes
(Table 3) and soil moisture subclasses (Table 4). These
classes were designed for well-drained mineral soils in
temperate areas.
| Extremely cold |
MAST1<-7°C
Continuous permafrost usually occurs below the active2 layer within 1 m of the surface
Very short growing season, <15 days >5°C
Remains frozen within the lower part of the control section
Cold to very cool summer, MSST3 <5°C
No warm thermal period >15°C |
| Very cold |
MAST -7-<2°C
Discontinuous permafrost may occur below the active layer within 1 m of the surface
Soils with Aquic regimes usually remain frozen within part of the control section
Short growing season, <120 days >5°C
Degree-days >5°C are <555
Moderately cool summer, MSST 5-<8°C
No warm thermal period >15°C |
| Cold |
MAST 2--<8°C
No permafrost
Undisturbed soils are usually frozen in some part of the control section for a part of the dormant season4
Soils with Aquic regimes may remain frozen for part of the growing season
Moderately short to moderately long growing season, 120-220 days >5°C
Degree-days >5°C are 555-<1250
Mild summer, MSST 8-<15°C
An insignificant or very short, warm thermal period, 0-50 days >15°C
Degree-days >15°C are <30 |
| Cool |
MAST 5-<8°C
Undisturbed soils may or may not be frozen in part of the control section for a short part of the dormant season
Moderately short to moderately long growing season, 170-220 days >5°C
Degree-days >5°C are 1250-<1720
Mild to moderately warm summer, MSST 15-<18°C
Significant very short to short warm thermal period, <120 days >15°C
Degree-days >15°C are 30-220 |
| Mild |
MAST 8-<15°C
Undisturbed soils are rarely frozen during the dormant season
Moderately long to nearly continuous growing season, 200-365 days >5°C
Degree-days >5°C are 1720-2775
Moderately warm to warm summer, MSST 15-<22°C
Short to moderately warm thermal period, <180 days >15°C
Degree-days >15°C are 170-670 |
| AQUEOUS |
Free water standing continuously on the soil surface |
| AQUIC |
Soil is saturated for significant periods of the growing season |
| Peraquic |
Soil is saturated for very long periods
Ground water level is at or within the capillary reach of the surface |
| Aquic |
Soil is saturated for moderately long periods |
| Subaquic |
Soil is saturated for short periods |
| MOIST UNSATURATED |
Varying periods of intensities of water deficits during the growing season |
| Perhumid |
No significant water deficits in the growing season
Water deficits <2.5 cm; CMI1 >84 |
| Humid |
Very slight deficits in the growing season
Water deficits 2.5-<6.5 cm; CMI1 74-84 |
| Subhumid |
Significant deficits in the growing season
Water deficits 6.5-<13 cm; CMI1 59-73 |
| Semiarid |
Moderately severe deficits in the growing season
Water deficits 13-<19 cm; CMI1 46-58 |
| Subarid |
Severe deficits in the growing season
Water deficits 19-<38 cm in cool and cold regimes; 19-51 cm in mild regimes; CMI1 25-45 |
| Arid |
Very severe deficits in the growing season
Water deficits ≥38 cm in cool regimes and ≥51 cm in mild regimes; CMI1 <25 |
Therefore, Organic soils in mild regimes may have temperatures
equivalent to associated mineral soils. Elsewhere, Organic
soils probably are at least one temperature class colder than
associated imperfectly to well drained mineral soils.
The moisture subclasses in Table 4 are defined imprecisely
based on of the degree and duration of saturation. Table 5
gives guidelines for selecting the appropriate moisture
subclass in organic soils. These criteria apply to the surface
tier.
The particle-size classes that are to be recognized at the
family level for mineral material in Terric1
subgroups of Organic soils are fragmental, sandy,
sandy-skeletal, loamy, loamy-skeletal, clayey, and
clayey-skeletal.
1 = An unconsolidated mineral layer at least 30 cm thick
beneath the surface tier.
Limnic layer classes apply only to the Limnic subgroups of
Organic soils and are marl, diatomaceous earth, and
coprogenous earth. The definitions of these materials may
be found in Chapter 2 under "Named layers and materials of
Organic soils." Note the exclusion from the Organic order
of soils in which mineral sediment, marl, or diatomaceous
earth layers thicker than 40 cm occur at the surface or
that have mineral sediment, marl, or diatomaceous earth
layers thicker than 40 cm within the upper 80 cm of the
control section.
Depth classes are applicable only in organic soils having a
lithic contact or permafrost within a depth of 160 cm and
are measured from the surface to the contact layer.
| Extremely shallow lithic |
10-40 |
| Very shallow lithic |
40-100 |
| Shallow lithic |
100-160 |
| Extremely shallow cryic |
10-40 |
| Very shallow cryic |
40-100 |
| Shallow cryic |
100-160 |
The technical soil family name is descriptive and consists
of the subgroup name followed by several adjectives
designating the mineral or organic family classes and
subclasses, and should be terminated by the term family.
The classes and subclasses are listed in the following
order:
- Mineral soils; particle size, mineralogy, depth, reaction, calcareousness, soil temperature, and soil moisture regime.
- Organic soils; characteristics of surface tier, reaction, soil temperature, soil moisture regime, particle-size of terric layer, limnic material, and depth.
Some of the modifiers are not necessary for some subgroups;
for example, the reaction class should not be indicated for
Alkaline Solonetzs. Some examples of family names are
- Orthic Humo-Ferric Podzol, coarse-loamy, mixed, acid, cool, perhumid family.
- Orthic Eutric Brunisol, coarse-silty over sandy, mixed, shallow, strongly calcareous, cold humid family.
- Terric Mesisol, humic, dysic, cool, aquic, loamy-skeletal family.
- Limnic Humisol, humic, euic, mild, aquic, coprogenous family.
A family thus described is a taxonomic entity within which
from one to a large number of series may be established.
Like the series, its suitability as a basis for naming pure
or complex mapping units varies from region to region and
according to the scale of mapping.
In some instances it is useful to indicate phases of families
(see Chapter 15, Soil Phase). This is done by adding,
after the term family, the appropriate phase terms and
"phase." An example is
- Orthic Humo-Ferric Podzol, coarse-loamy, mixed, acid, cool, perhumid family; peaty, level phase.
For convenience and brevity the name of a common series may
be used to designate a family. For example, it is acceptable
to refer to "Breton family" to indicate the Orthic
Gray Luvisol, fine-loamy, mixed, neutral, cold, subhumid
family.
| Descriptive condition |
Free surface water |
Saturated for very long periods |
Saturated for moderately long periods |
Saturated for short periods |
Moist with no significant seasonal deficit |
Moist with no significant seasonal deficit |
| Drainage class |
|
Very poorly drained |
Poorly drained |
Imperfectly drained |
Imperfectly to moderately well drained |
Moderately well drained |
| Suggested criteria |
| Saturated period |
Continuous |
Very long |
Long to moderately short |
Short to very short |
Very short |
Very short to insignificant |
| Months per year |
11.5-12 |
>10 |
4-10 |
<4 |
<2 |
<0.5 |
| Moist period |
insignificant |
Very short |
Short to moderately long |
Long to very long |
Long to very long |
very long |
| Months per year |
<0.5 |
<2 |
2-8 |
8-11.5 |
8-11.5 |
>11.5 |
| |
| Associated native vegetation |
Hydrophytic |
Hydrophytic |
Hydrophytic to mesophytic |
Hydrophytic to mesophytic |
Mesophytic |
Mesophytic |
| |
Nymphaea, Potamogeton, Scirpus, Typha, Phragmites, Drepanocladus |
Scirpus, Typha, Carex, Drepanocladus, Feather mosses, Larix |
Wet black spruce forest, mixed feather and sphagnum mosses, Ericaceous shrubs |
Wet to very moist black spruce forest, sphagnum mosses, Ericaceous shrubs |
Moist black spruce forest, mixed sphagnum and feather mosses, Ericaceous shrubs, lichens |
Disturbed species, Cultivated species |
| |
| Associated peat landform |
Wetlands, marsh, floating fen, collapse scars |
Flat fens, patterned fens, spring fens, swamps |
Blanket bogs, transitional bogs |
Domes bogs, plateaus |
Frozen plateaus, frozen palsas, frozen peat polygons |
Drained peat land, Folisols |
The concept of the soil series has changed greatly since the
early 1900s when a series was somewhat analogous to a
geological formation. Now the series is a category in the
system of soil taxonomy in the same way that order, great
group, subgroup, and family are categories. A soil series
is a conceptual class that has, or should have, defined
limits in the same way as a great group. The link between
the conceptual entity, soil series, and real bodies of soil
is the pedon. Any pedon may be classified as a unique soil
series, but series have been named for only a very small
proportion of the kinds of pedons that occur.
Soil series are subdivisions of soil families based upon
relatively detailed properties of the pedon within the depth
of the control section. The range of variability of the
differentiating characteristics is narrower for the series
than for the family. Series cannot transgress soil climatic
and particle-size classes, or other boundaries recognized in
family separations. The significance of differences in the
properties of the different kinds of pedons that fall within
a soil family depends on how these properties combine. No
specific property, or group of properties, has been assigned
limits and been used consistently from family to family and
within families to define series. Each potential soil series
is treated as an individual case and the decision on whether
or not it should be recognized as a separate taxon involves
a judgment based on the following guidelines:
- The properties that distinguish a particular series from
other series must be sufficiently recognizable that
qualified pedologists can identify the series
consistently.
- The properties used to differentiate series must be
within the control section (see 4 and 5 below).
- Soils of a series must occupy at least a few hundred
hectares. Establishing a series to classify a few pedons
that occupy a few hectares is not justified even if the
pedons have unique properties.
- Soil series within families of mineral soils are usually
differentiated based on the following properties:
- color, including mottling;
- texture;
- structure;
- consistence;
- thickness, relative arrangement of horizons, and
degree of expression of horizons and of the solum;
- abundance and size of coarse fragments;
- depth to a lithic contact, permafrost, or contrasting
material to a finer degree than used in higher
categories;
- depth to, and concentration of free carbonates;
- depth to, and concentration of soluble salts;
- reaction (pH);
- lithology.
- Soil series within families of Organic soils may be
differentiated based on the following properties:
- material composition - botanical origin of fibers
and nature of terric layer, if any;
- thickness, amount of decomposition and relative
arrangement of layers;
- abundance of woody material-logs and stumps;
- calcareousness;
- bulk density;
- mineral content of organic material;
- soil development in the terric layer;
- mineralogy of terric or cumulic layers;
- texture of terric or cumulic layers;
- reaction (pH).
Few series of Organic soils have been established and it is
likely that other series criteria will emerge.
Pedons classified as a given soil series have a similar
number and arrangement of horizons whose color, texture,
structure, consistence, thickness, reaction, or some
combination of these properties are within a defined range.
In the case of soils without genetic horizons, the above
statement applies to the C horizons to the depth of the
control section.
The concept of the soil series has been refined progressively
in Canada throughout the last half century. Many
"series" established 30 or more years ago might
include pedons that belong to several subgroups or families
today. Years ago soil taxonomy was focused on the series
and the great group; much less attention was given to other
categories. Series were differentiated without reference to
family criteria, which were not developed until recently.
Thus many of the "series" used today still include,
to a degree, the attributes of the more generalized series of
several years ago. In the process of establishing new series
and refining old series today, the pedologist should work
downward in soil taxonomy considering the differentiation
of soil properties at the order, great group, subgroup, and
family levels before subdividing the family into series.
Taxonomy will probably not be extended to the series level
in many medium- to small-scale soil surveys. For more detailed
work, the series is a category of paramount importance because
it is the most specific level in soil taxonomy and the one
used for most interpretations. Sound judgments, based upon
the guidelines stated, on the part of soil mappers and
correlators are essential in decisions on establishing series.
The definition of a series implies a statement of the limits
of its properties.
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