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VI. Bases for Proposed Classification System

VI. Bases for Proposed Classification System

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144



R. S. FARNHAM AND H. R. FINNEY



1. The main emphasis in this system is on morphological properties

of certain diagnostic horizons, not on botanical remains, geology, topography, or chemistry of bog waters.

2. The object classified is a three-dimensional body occurring on

organic terrain which has certain designated thickness limits.

3. The system uses as many semiquantitative to quantitative evaluations as necessary so that good precision is both possible and reproducible.

4. Classes are carefully selected which are clearly and repeatedly

distinguishable.

5. The system is basically designed for use in making detailed soil

surveys but is also useful for broad groupings of organic soils. This is

not necessarily an objective in many other organic soil classification

systems.

A. NOMENCLATURE

The system of nomenclature for a new classification system is important since it greatly affects its acceptance and utility. The nomenclature used in this system is based on that proposed by the Soil Survey

Staff (1960), which, according to G. D. Smith (1963), is based on the

following principles:

1. The formative elements were to come from the classical languages

insofar as possible, so that the names might be mnemonic and connote

some of the properties, and so that they would fit readily into as many

modern languages as possible and be distinctive.

2. The name should indicate the place of a taxon in the system.

From the name, one should be able to recognize both the category of the

taxon and the taxa in any of the higher categories to which it belongs.

3. The names should be as short as possible. This is critical in the

higher categories if the names of taxa in lower categories are to be

manageable in speech.

4. The names should be as euphonic as possible.

5. Existing terms were to be avoided.

Names used for organic horizons are taken from the classical Ianguages (Greek and Latin) with the suffixic to form adjectilles. The name

fibric comes from the Latin wQrd fibru (fiber containing); the name

mesic comes from the Greek word meso (intermediate), which implies

intermediate stage of decomposition; and the name sapric comes from

the Greek word supros (rotted), which implies a high degree of decomposition.



B. BASICPRECEPTS

The basic precepts or guidelines for the proposed organic soil classification system include the following:

1. Definition of organic soil (Histosol): a soil with over 20 to 30



CLASSIFICATION OF ORGANIC SOILS



145



per cent organic matter that is at least 12 inches in thickness. Organic

matter requirement depends on texture of mineral fraction; 20 per cent

if horizon contains no clay, and 30 per cent if horizon contains over 50

per cent clay, with proportional values for textures between the two

limits. This distinguishes organic soils from mineral soils.

2. For practical reasons an arbitrary control section is classified, not

the entire organic deposit. The thickness limits of the control section

are 40 inches if drained and 60 inches if undrained. These limits certainly

include that portion of these soils where maximum microbiological

activity occurs and where most of the roots of economic plants grow.

3. Organic horizons are diagnostic in the system if they are sufficiently homogeneous in respect to morphological features and are at

least 12 inches (30 cm.) in thickness [18 inches (45 cm.) if undrained].

4. Emphasis is given to the more stable subsurface (12 to 40 inches,

drained or 18 to 60 inches, undrained) part of the control section in the

higher taxa of the system because the surface horizon may change

rapidly through farming practices, drainage, etc.

5. In control sections with two diagnostic subsurface horizons the

most stable (most decomposed) horizon receives precedence in naming

classes at the Suborder level. Diagnostic sapric horizons take precedence

over mesic horizons, and mesic over fibric.

6. Nonorganic horizons occurring in the arbitrary control section of

an organic soil must be considered in the classification system at the

subgroup level. For example, limnic material, buried mineral soils, bog

iron, and volcanic ash are considered intergrades between organic and

mineral soils.

7. Surface horizons (epipedons) of organic soils are considered only

at the type level in the system. Morphological properties significant to use

of these soils form the basic differentiae for classes. Such features as kind

of fiber, decomposition stage, base status, and calcareousness are used.

In the highest category of the system, Order, the name Histosol is

used. This word is taken from the Greek word histos, which means tissue

and in this case implies plant tissue. Hence the name means a soil

containing varying amounts of plant tissue in contrast to mineral soils

which are generally devoid of plant tissue except in the surface horizons.

Principal criteria used in various categories are summarized in Table XI,

and a list of names proposed for the various categories are shown in

Table XII.

In the next highest category, Suborder, the formative element of

histosol ist was chosen as the ending for names of the various classes.

Classes of the suborder include Fibrid, which is a soil containing a

diagnostic subsurface fibric type horizon but lacks a diagnostic subsur-



146



R. S. FARNHAM AND H. R. FINNEP



face mesic or sapric horizon; Mesist, which contains a diagnostic subsurface mesic horizon but lacks a diagnostic subsurface sapric horizon;

Saprist, which contains a diagnostic subsurface sapric horizon; and

Leptist, which lacks any diagnostic subsurface horizon either because the

organic subsurface portion of the control section is not thick enough

to be diagnostic or, in the case of a thick organic soil, is not sufficiently

homogeneous to have a diagnostic subsurface organic horizon.

TABLE XI

Principal Criteria in Various Categories of Histosols

Category

Order

Suborder

Great Group

Subgroup



Family

Series



Criteria

Minimum thickness 30 cm. (12 inches) drained or 45 cm. (18

inches) undrained; organic content 20 to 30 per cent

Presence or absence of diagnostic organic horizons and kinds of

subsurface horizons

Base status of diagnostic subsurface horizon or, if lacking,

dominant horizon type, permafrost, or cool summer temperatures

Kinds of control sections-all

organic (Typic) or contrasting

substrata such as organic upper portion in superposition over

mineral soil (Thaptic), lake deposits (Limnic), rock (Lithic),

or all organic with high mineral content (elastic)

Nature, texture, and mineralogy of substrata and gross fiber

composition

Base status, thickness, uniformity, and specific fiber composition

of subsurface horizons



In the next level, Great Group, classes have names, derived from

the classic languages, which denote or imply base status, climate, and

presence of certain specific botanical remains. The meaning of the prefixes dys and eu were discussed in Section V, A, 3. Classes with prefix

q o (from Greek word cryos meaning cold) are used for soils of cold

regions having mean summer soil temperatures at 20 inches less than

60°F. or that contain permafrost.

Two coined terms implying specific plant fiber are used in the

Fibrist group-sphgno and hypno. The Sphgnofibrist is a Fibrist organic soil containing a diagnostic subsurface sphagnofibric horizon composed chiefly of remains from Sphagnum mosses. It is always low in

bases, and the pH is extremely low. The Hypnofibrist is a fibrist soil

containing a diagnostic subsurface hypnofibric horizon composed of

Hypnum moss fibers. They are always high in bases, and the pH (1N

KCl) is above 5.0.

In the next lower level of the system, Subgroup, classes are distinguished essentially on the basis of whether the entire control section is

organic or not, of arrangement of organic horizons, and of kinds of



147

contrasting material below the organic portion of the control section. For

the Cyic classes, however, pH is also used. Following are the classes:

CLASSIFICATION OF ORGANIC SOILS



A. Soils with diagnostic subsurface organic horizons ( Saprists, Mesists, Fibrists)

1. Typic classes comprise soils with all organic control sections which are composed of only one kind of diagnostic subsurface organic horizons.

2. Clustic (from Greek word klnstos, meaning fragments of rock; geological definition: fragmental, composed of discrete grains that have been transported

to site of deposition) classes comprise soils that contain from 50 to 70 or 80

per cent (depending on texture) mineral matter.

3. Limnic (from Creek word limms, meaning lake) classes comprise soils that

have within the control section materials such as marl, sedimentary organics,

diatomite, pumicite, bog iron. These materials occur beneath the organic portion of the control section.

4. Thaptic (from Greek word thuptos, meaning buried) classes comprise soils

containing buried mineral soils within the control section; names used are the

same as those used in the proposed classification scheme of the Soil Survey

Staff ( 1960). An example is Thapto Aquollic EusuprNist.

5. Lithic (from Greek word Zithos, which implies rock) classes comprise soils

that contain (bed) rock within the control section.

6. Znteric (from Latin word inter, meaning among or between) classes comprise soils with two diagnostic subsurface horizons. An example is Interic

Mesic Eusaprist which has both diagnostic sapric and mesic subsurface

horizons.

7. Dysic classes comprise only C y i c soils. They contain subsurface organic horizons with a p H (KC1) of 5.0 or less.

8. Euic classes comprise only Cryic soils. They contan subsurface organic horizons with a pH (KC1) of more than 5.0. It should b e noted that the names

of Cryic soils at this level will consist of three words. For example, there

would be both a Typic Dysic Cryosuprist and a Typic Euic Cryosap7ist. This

may well not b e the best way of handling these, and pH might best be a

differentia at the family level for these soils.

B. Soils lacking diagnostic subsurface horizons (Leptists)

1. Typic classes comprise thin, less than 24 inches drained and 36 inches undrained, organic soils overlying mineral material or a limnic horizon; they

contain only one kind of organic horizon, which is 12 inches or more thick.

The kind of organic horizon is indicated in the Great Group name. In addition, they lack a lithic contact in the control section, and the organic portion

of the control section contains less than 50 per cent mineral matter.

2. Thaptic classes comprise thin, less than 24 inches drained and 36 inches

undrained, organic soils overlying a mineral soil; they contain two or more

organic horizons aggregating 12 inches or more, one of which dominates as

indicated by the Great Group name. They lack either a limnic horizon or a

lithic contact in the control section, and the organic horizons contain less

than 50 per cent mineral matter.

3. Clastic classes comprise thin, less than 24 inches drained and 36 inches undrained, organic soils overlying a mineral soil or a limnic horizon. They lack

a lithic contact, and the organic portion of the control section contains 50

to 70 (to 80) per cent mineral matter.

4. Limnic classes comprise thin organic soils like those of the Thaptic class, but

they are underlain by a limnic horizon instead of a mineral soil.



TABLE XI1

Proposed Names for the Higher Categories of Histosols



Order

10 Histosols



Suborder

A. Soils with diagnostic

subsurface horizons

10.1 Saprists



Great Group



10.11 Cryosaprists

10.12 Dysaprists

10.13 Eusaprists



Subgroup

(terms used as adjectives

with Great Group names)



Typic

Clastic

Limnic

Thaptic

Lithic

Interic

Dysic

Euic



10.2 Mesists



10.21 Cryomesists

10.22 Dysmesists

10.23 Eumesists



Typic

Ciastic

Limnic

Thaptic

Lithic

Interic

Dysic

Euic



10.3 Fibrists



10.31 Cryofibrists

10.32 Sphagnofibrists

10.33 Hypnofibrists

10.34 Dysfibrists

10.35 Eufibrists



E



m

v,

R1



I

4



3

m



I



Cryomesists only



Typic

Clastic

Limnic

Thaptic

Lithic

Interic

Cryofibrists only



TABLE XI1 (continued)



Order

10 Histosols

(continued)



Suborder



Great Group



Subgroup

(terms used as adjectives

with Great Group names)



B. Soils lacking diagnostic

subsurface horizons

10.4 Leptists



P

km



3n



*



10.41 Crysaproleptists

10.42 Crymesoleptists

10.43 Cryfibroleptists

10.44 Dysaproleptists

10.45 Dysmesoleptists

10.46 Dysfibroleptists

10.47 Eusaproleptists

10.48 Eumesoleptists

10.49 Eufibroleptists



g



Typic

Clastic

Limnic

Thaptic

Stratic

Cumulic

Lithic



8

80



*2:



ri

Crysaproleptists,

Crymesoleptists,

and Cryfibroleptists

only



v1



8



150



R. S. FARNHAM AND H. R . FINNEY



5. Strutic classes comprise thick organic soils, 40 inches drained and 60 inches



undrained, lacking diagnostic horizons, that is, horizons less than 12 inches

drained and 18 inches undrained. They have thin alternating layers of

organic horizons occupying the entire control section, which is dominated

by the particular organic horizon designated in the Great Group name.

6. Cumulic classes comprise thick organic soils lacking limnic or thaptic horizons

and a lithic contact, and they consist of strata of thin organic and mineral

layers to the base of the control section.

7. Lithic classes comprise other thin organic soils with a lithic contact within

the control section.

8. Dysic and Euic classes are used only with the Cryic soils as described in items

7 and 8 under soils with diagnostic subsurface horizons.



C. APPLICATIONOF THE SYSTEM

This proposed classification system for organic soils (Histosols) is

specifically designed for field use, especially in making soil maps. Decisions concerning various differentiae can be made in the field by the soil

surveyor using conventional survey equipment, such as augers, color

books, pH kits, and in addition a spot plate for making sodium pyrophosphate tests.

In order to distinguish one soil from another it is necessary to examine

the organic soil to only 40 inches drained or 60 inches undrained. Identification of diagnostic horizon types in these arbitrary control sections

is made by determining the homogeneity and thickness of a particular

horizon, its fiber content, pH, stage of decomposition as measured by

sodium pyrophosphate, and other morphological features significant to

classification.

Like soils are separated from unlike soils on the map by drawing

boundaries. Thus the various cartographic units are separated from one

another, and the bases for the distinction represent an expression of

different morphological features diagnostic in the taxonomic system.

Several sites within a given area are examined carefully in order to

determine the homogeneity and juxtaposition of specific kinds of horizons

within the control section.

Descriptions of five representative organic soils are given:

ORGANIC

SOILNo. 1

Typic Sphagnofibrist

Location:



NE 1/4, Sec. 2, T42N, R22W Aitkin Co., Minnesota, along U.S. No. 2

near Wawina



Physiography: Raised portion of large bog in glacial Lake Upham basin

Surface vegetation:



Stunted black spruce (Picea muriona), leather leaf (Chumuedaphne calyculata ) , Labrador tea ( Ledum groenlundicum ) ,

and several species of Sphagnum mosses



CLASSIFICATION OF ORGANIC SOILS



151



Description: Undrained (60” control section)

0-6”: Brown (lOYR 4/3, moist), light gray ( lOYR 7/2) when pressed firmly;

relatively unaltered plant remains, fiber content 95 per cent, chiefly from

Sphagnum mosses; few leaves and wood fragments from Labrador tea

and leather leaf; sodium pyrophosphate extract on white filter paper

lOYR 8/2; pH ( 1 N KCl) 2.8

6-78”: Dark reddish brown (5YR 3/2, moist), pinkish gray (7.5YR 6/2) when

pressed firmly; slightly altered plant remains from Sphagnum mosses

with fiber content over 90 per cent; few small roots of heath plants and

bark and cones of black spruce; very thin (less than 2”) strata of more

decomposed plant remains near top of horizon; sodium pyrophosphate

extract on white filter paper is lOYR 8/3; p H ( 1 N KCl) 2.6

Key to classification

0-18” surface:

18-60” subsurface:



Surface sphagnofibric horizon p H (1.0 N KCl) 2.8

Diagnostic sphagnofibric horizon pH ( 1 N KCI) 2.6

Fiber content 90 per cent, sodium pyrophosphate extract on

white filter paper is higher in value or lower in chroma than

lOYR 7/3 (Munsell)

Taxonomic classification

Order level:

10 Histosol

Suborder level:

10.3 Fibrist

Great Croup level: 10.32 Sphagnofibrist

Subgroup level:

10.320 Typic Sphagnofibrist

ORGANICSOIL No. 2



Typic Dysmesist

SW 1/4, Sec. 31, T48N, R26W, 5 miles N of Aitkin, north of flood control

canal-Aitkin Co., Minnesota

Physiography: Large open bog in glacial Lake Aitkin

Location:



Description: Drained ( 40” control section)

0-10“: Dark reddish brown (5YR 2/2, moist) base fiber color, very dark gray

(5YR 3/1) to dark reddish brown (5YR 3/2) rubbed; fiber content 40

to 50 per cent of total organic material; streaks of sapric material are

black (5YR 2/1, moist) and discontinuous; many fine roots of modem

flora (sedges and grasses) in upper part of horizon; sodium pyrophosphate extract on white filter paper is lOYR 8/2; pH ( 1 N KCl) 4.9

Dark brown to brown (7.5YR 3/2-4/4, moist) base fiber color; content

10-16“:

of fibers 50 to 60 per cent; very dark gray (lOYR 3/1, moist) rubbed;

most fibers destroyed on rubbing; few fine wood fragments; p H

( 1 N KC1) 4.7

16-22”: Dark brown, brown to strong brown (7.5YR 3/2, 4/4, 5/6 moist) base

fiber colors, dark brown (7.5YR 3/2) rubbed; fiber content 80 per cent

before rubbing; fibers easily disintegrate on rubbing; pH ( 1 N KCl) 4.5

22-44”: Dark brown and dark yellowish brown (lOYR 3/3 and 4/4) base fiber

colors; very dark gray (10YR 3/1) rubbed; fiber content 60 per cent;

few thin black (lOYR 2/1) layers; color becomes darker and fiber content is less with depth; sodium pyrophosphate extract on white filter

paper is higher in value and lower in chroma than lOYR 7/3; pH

( 1 N KCl) 4.9



152



R. S . FARNHAM AND H. R. YINNEY



Key to classification

0-10”: Surface mesic horizon, pH (KCl) 4.9 fiber content 40 to 50 per cent

10-40”: Subsurface diagnostic mesic horizon, p H ( KCl) 4.5-4.9, fiber content

50 to 80 per cent, fibers decrease in chroma when rubbed wet

Taxonomic classification

10 Histosol

Order level:

Suborder level:

10.2 Mesist

Great Group level: 10.22 Dysmesist

Subgroup level:

10.220 Typic Dysmesist



ORGANICSOIL No. 3

Thapto Aquollic Dysmesist

Location:



SW 1/4, NW 1/4, Sec. 12, T47N, R26W, Aitkin Co., Minnesota. Photo

AIT-3-81



Description: Drained bog (40” control section)

0-10”: Black (lOYR 2/1, moist) matrix of well decomposed organic material

with fibers of very dark brown (lOYR 2/2, moist); fiber constitutes 15

to 20 per cent of total material; rubbed color (wet) black ( lOYR 2/1);

pH ( 1 N KCl) 4.8

10-34”: Very dark brown (lOYR 2/2, moist) matrix with fibers of dark brown

(IOYR 3/3 and 7.5YR 3/3, moist); fiber content 50 to 60 per cent of

total; fiber easily disintegrates on rubbing wet and becomes finely divided and structureless, also darkens slightly on rubbing; pH ( 1 N KCl)

4.8

34-48”: Clay loam; buried mineral soil has 4” A1 and gley horizon (probably

Aquoll); p H ( 1 N KC1) 6.5

Key to classification

0-10: Sapric surface horizon, pH 4.8 (KCl) fiber content 15 to 20 per cent

10-34”: Diagnostic subsurface mesic horizon, pH 4.8 (KCl) fiber content 50 to

60 per cent, fibers darken on rubbing

Buried

clay loam mineral soil, high base saturation, pH 6.5 (KCl)

34-40”:

Taxonomic classification

10 Histosol

Order level:

Suborder level:

10.2 Mesist

Great Group level: 10.22 Dysmesist

10.22-5.3 Thupto Aquollic Dysrnesist

Subgroup level:

(Organic soil intergrading to wet mineral soil)

ORGANIC

SOILNo. 4



Thapto Aquollic Eusaproleptist

Location:



NE 1/4, NW 1/4, Sec. 8, T103N, RlQW, Freeborn Co., Minnesota



Physiography:



Large drained and cultivated level bog area in glacial lake plain.

Surrounding upland soils developed on highly calcareous glacial till,

sands, and gravels



153



CLASSIFICATION OF ORGANIC SOILS



Description: Drained bog (40” control section)

0-12”: Black (lOYR 2/1, moist) to very dark brown (lOYR 2/2, moist) rubbed

color same; finely divided organic material; fiber content less than 15

per cent; pH 8.3 (1 N KCl); sodium pyrophosphate extract on white

filter paper lOYR 5/3, moist

12-18: Dark reddish brown (5YR 3/3-3/4, moist) with lenses of black (lOYR

2/1, moist) rubbed color of wet fiber is black (lOYR 2/1); finely divided organic material between fibers; fiber content about 50 to 60 per

cent; most fibers disintegrate when rubbed; pH 8.2 ( 1 N KCl)

18-22”: Very dark gray (2.5Y 3/1, moist) silt loam with distinct yellowish brown

(lOYR 5/8, moist) mottles and dark brown (7.5YR 3/4) filled root

channels; massive; friable; slight to moderate effervescence; p H 7.5

(1 N KCl)

22-40”: Gray (lOYR 4/1, moist) silt loam with common, medium distinct yellowish brown (lOYR 5/8, moist) mottles; massive; friable; strong effervescence with dilute HCI, pH 8.0 ( 1 N KCl)

.



I



Key to classification

0-12”: Surface sapric horizon, fiber less than 15 per cent, sodium pyrophosphate

test indicates high degree of decomposition, pH 8.3 ( 1 N KCl)

12-18”: Thin nondiagnostic (less than 12”) subsurface mesic horizon, fiber content 50 to 80 per cent, fibers darken on rubbing; p H 8.2 ( 1 N KCl)

18-22”: Buried surface horizon of silt loam mineral soil with high base saturation

22-40”: Buried gley horizon of mineral soil (Aquoll)

Taxonomic classification

Order level:

10 Histosol

Suborder level:

10.4 Leptist

Great Group level: 10.47 Eusuproleptist

10.47-5.3 Thupto Aquollic Eusaproleptist

Subgroup level:

(Organic soil intergrading to wet mineral soil)



ORGANICSOIL No. 5

Typic Eusuprist



Location:



NW 1/2, NW 1/2, Sec. 12, T103N, R20W, Freeborn Co., Minnesota



Physiography:



Large drained and cultivated level bog area in glacial lake plain.

Area cropped to vegetables such as potatoes, onions, and asparagus



Description: Drained bog (40” control section)

0-10”: Black (lOYR 2/1, moist), very dark gray (lOYR 3/1, dry) finely divided

organic material; fiber content less than 10 per cent; mineral content

about 30 to 40 per cent; sodium pyrophosphate extract on white filter

paper lOYR 4/3, moist; p H 6.6 ( 1 N KCl)

1&40”: Black (lOYR 2/1, moist) to very dark brown (lOYR 2/2, moist), very

dark gray (lOYR 3/1, dry) finely divided organic material; fiber content 10 to 20 per cent; mineral content about 20 to 30 per cent; pH

8.3 ( 1 N KC1); sodium pyrophosphate extract on white filter paper

lOYR 3/4, moist



154



R. S. FARNHAM AND H. R. FINNEY



Key to classification

0-10: Surface sapric horizon; high base status pH 6.6 ( 1 N KCl); fiber

content less than 33 1/3 per cent; highly decomposed as measured by

sodium pyrophosphate test

10-40”: Diagnostic subsurface sapric horizon; high base status, pH 6.3 ( 1 N

KC1); fiber content less than 33 1/3 per cent highly decomposed as

measured by sodium pyrophosphate test; low mineral content organic

horizon

Taxonomic classification

10 Histowl

Order level:

Suborder level:

10.1 Sapfist

Great Group level: 10.13 Eusuprht

Subgroup level:

10.130 Typic Eusaprist



A trial application of the proposed organic soil classification system

in undeveloped areas of the glacial Lake Agassiz basin which still contain

their original vegetation was made by the authors. Figure 2 shows the

soil boundaries drawn on an aerial photograph base map. Tonal patterns



FIG. 2. An area of peatland in the glacial lake Agassiz basin, Koochiching

County, northern Minnesota. Note the tonal patterns which give a clue to different

kinds of organic soils. Soils occurring in cartographic units I, 2, and 3 are discussed

in Section VI, C. The dark tone and stippled pattern in unit 3 is from dense black

spruce with an understory of Sphagnum species and heath plants. Vegetation in unit

2 is a stunted, open stand of black spruce, heaths and Sphagnum species, and in

unit I, it is reeds, sedges, and heath plants. A cross section along A-A’ is shown

in Fig. 3.



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