Chapter 14: Soil Family and Series

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.

Family Criteria and Guidelines for Mineral Soils

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).

Particle size classes

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:

Fragmental Stones (>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.

Sandy-skeletal 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.

Loamy-skeletal 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.

Clayey-skeletal 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.

Sandy 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).

Loamy 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).

Coarse-loamy 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.
Fine-loamy 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.
Coarse-silty 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.
Fine-silty 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.

Clayey The fine earth contains 35% or more (by weight) clay¹ and particles >2 mm occupy less than 35% (by volume).

Fine-clayey A clayey particle size that has 35-60% (by weight) clay¹ in the fine earth fraction.
Very-fine-clayey A clayey particle size that has 60% or more (by weight) clay¹ in the fine earth fraction.

Substitute classes for particle-size and Mineralogy

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.

Cindery 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.

Ashy 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.

Ashy-skeletal Particles >2 mm in diameter, other than cinders, occupy 35% or more (by volume); the fine earth fraction is ashy as defined above.

Thixotropic 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.

Thixotropic-skeletal Particles >2 mm in diameter, other than cinders, occupy 35% or more (by volume); the fine earth fraction is thixotropic as defined above.

Application of particle-size classes and substitute classes

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
1. a lithic contact, particle size is assessed in all of the mineral material above the lithic contact;
2. 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
1. a depth of 1 m;
2. a lithic contact; or
3. 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
1. 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;
2. 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;
3. 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
1. a depth of 1 m; or
2. a lithic contact, whichever is shallower.

Strongly contrasting particle-size classes and substitute classes

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.

Mineralogy classes

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

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:

Class	Depth (cm)
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

Reaction classes

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.

Class	pH
Acid	<5.5
Neutral	5.5-7.4
Alkaline	>7.4

Table 1. Strongly contrasting particle sizes

Loamy

Clayey

F
R
A
G
M
E
N
T
A
L

S
A
N
D
Y
-
S
K
E
L
E
T
A
L

L
O
A
M
Y
-
S
K
E
L
E
T
A
L

C
L
A
Y
E
Y
-
S
K
E
L
E
T
A
L

S
A
N
D
Y

C
O
A
R
S
E
-
L
O
A
M
Y

C
O
A
R
S
E
-
S
I
L
T
Y

F
I
N
E
-
L
O
A
M
Y

F
I
N
E
-
S
I
L
T
Y

F
I
N
E
-
C
L
A
Y
E
Y

V
E
R
Y

F
I
N
E
-
C
L
A
Y
E
Y

C
I
N
D
E
R
Y

A
S
H
Y

T
H
I
X
O
T
R
O
P
I
C

Over³

Fragmental

X¹

X²

Sandy-skeletal

Loamy-skeletal

Clayey-skeletal

Sandy

Loamy

Clayey

Cindery

Table 2 Key to mineralogy classes
Class	Definition	Determinant particle-size fraction
Classes applied to soil families of any particle-size class
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
Classes applied to soil families having a fragmental, sandy, sandy-skeletal, loamy, or loamy-skeletal particle-size class
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
Classes applied to soil families having a clayey² or clayey-skeletal particle-size class
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
1 = Percentages by weight are estimated from grain counts. Usually a count of one or two of the dominant size fractions of a conventional mechanical analysis is sufficient to place the soil.
2 = The clay mineralogy descriptions for clayey soils are based on the weighted average percentage of the particle-size control section of the fine earth fraction (≤2.0 mm).

Calcareous classes

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.

Class	CaCO₃ equivalent (%)
Weakly calcareous	1-6
Strongly calcareous	>6-40
Extremely calcareous	>40

The class extremely calcareous is redundant in soils with carbonatic mineralogy.

Soil climate classes and subclasses of mineral soils

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 and Guidelines for Organic Soils

Family criteria apply to the organic control section as defined in Chapter 2.

Characteristics of surface tier

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

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.

Class	pH
Euic	≥4.5
Dysic	<4.5

Soil climate classes and subclasses of organic soils

Table 3 Soil temperature classes
Class	Description
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
1 = MAST: mean annual soil temperature.
2 = Segment of the soil seasonally frozen and thawed.
3 = MSST: mean summer soil temperature.
4 = Dormant season <5°C.

Table 4 Soil moisture subclasses

REGIME/Subclass

Description

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

1 The term Climatic Moisture Index (CMI) expresses the growing season (>5°C) precipitation as a percentage of the potential water used by annual crops, when water is readily available from the soil.

CMI =	P	x 100
	P + SM + IR

P = growing season precipitation.

SM= water available to crops that is stored in the soil at the beginning of the growing season.

IR = irrigation requirements or water deficit for the growing season.

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.

Particle-size classes of terric layer

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

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

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.

Class	Depth (cm)
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

Nomenclature for Soil Families

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.

Table 5 Moisture subclasses as applied to organic soils
Soil moisture regime	Aqueous	Aquic			Moist soils
Classification	Aqueous	Peraquic	Aquic	Subaquic	Perhumid	Humid
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

Soil Series

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:
1. color, including mottling;
2. texture;
3. structure;
4. consistence;
5. thickness, relative arrangement of horizons, and degree of expression of horizons and of the solum;
6. abundance and size of coarse fragments;
7. depth to a lithic contact, permafrost, or contrasting material to a finer degree than used in higher categories;
8. depth to, and concentration of free carbonates;
9. depth to, and concentration of soluble salts;
10. reaction (pH);
11. lithology.
Soil series within families of Organic soils may be differentiated based on the following properties:
1. material composition - botanical origin of fibers and nature of terric layer, if any;
2. thickness, amount of decomposition and relative arrangement of layers;
3. abundance of woody material-logs and stumps;
4. calcareousness;
5. bulk density;
6. mineral content of organic material;
7. soil development in the terric layer;
8. mineralogy of terric or cumulic layers;
9. texture of terric or cumulic layers;
10. 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.

Links:
Learning Resources > CSSC > Chapter 14