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III. Criteria Used in Classifying Organic Soils

III. Criteria Used in Classifying Organic Soils

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118



R. S. FARNHAM AND H. R. FINNEY



fact that the various schemes represent the efforts of workers, with different objectives in classification, from various fields of endeavor such as

botany, geology, and the several branches of soil science. In order to

review concepts used in the past, some representative classification

schemes are discussed under the several headings below. This review

is indeed not extensive in references listed, but it is extensive in the

criteria used in classification. Works reported below are placed in the

various topic headings because of the bias used in the highest category,

even though the scheme discussed may embrace characteristics from one

or more of the other criteria.

An important factor for the reader to consider in the various schemes

presented is that many of them classify kinds of peatland (as defined by

Heinselman, 1963) rather than kinds of organic soils. Pyavchenko (1963)

and Farnham (1963), for example, have emphasized the fact that the

classification of peatland and of organic soils should be two separate

endeavors. It can be noticed in some of the schemes reviewed that the

classes at one level in the scheme represent kinds of peatland, whereas

classes at some other level in the same scheme are kinds of organic

soil. Furthermore, some schemes deal with peatland or with organic

soils throughout. In this review, the terms peat or peat soils and

organic soils are used synonymously.

A. TOPOGRAPHICAL-GEOGRAPHICAL

Schemes based on topographical-geographical features are most often

ones that differentiate kinds of peatlands. Shaler (lSW), a geologist

engaged in early inventories of peat resources of the United States, used

the following scheme:

I. Marine marshes

A. Above meantide

1. Grass marshes

2. Mangrove marshes

B. Below meantide

1. Mud banks

2. Eel grass areas

11. Freshwater swamps

A. River swamps

1. Terrace swamps

2. Estuary swamps

B. Lake swamps

1. Lake margin

2. Quaking bogs

C. Upland swamps

1. Wet woods

2. Climbing bogs

D. Ablation swamps



CLASSIFICATION OF ORGANIC SOILS



119



Weber (1903), a German worker, divided bogs into three types

based on surface configuration. The types are low moor, transitional moor,

and high moor. Supposedly the central portion of the low moor is at

a lower elevation than the peat-mineral soil boundary, whereas the

central portion of the high moor occupies an elevation greater than the

peat-mineral soil boundary. The transition moor is intermediate in that

respect. Supposedly, in development, a bog begins in the low moor

stage, then passes to the transitional, and finally to the high moor stage.

In the low moor stage, it develops in the presence of ground water and

alluvial sediments rich in minerals. In the high moor stage, however,

the source of nutrients is the atmosphere.

The concepts introduced by Weber’s scheme have been utilized to

varying degrees by many workers since that time. For example, Instorf,

the Soviet Institute of Peat Industry, as reported by Kazakov (1953)

and Tyuremnov ( 1963), uses a scheme with the following categories of

peat classification:

I. Low moor type

A. Forest subtype

B. Forest swamp subtype

C. Swamp subtype

11. Transitional type

111. Mixed type

IV. High moor type



The various subtypes are essentially expressions of surface vegetation.

Also, these subtypes are further subdivided into a total of 22 classes

based on kind of peat and its stratigraphy. It might be noted that the

approach to peat classification used by Instorf is rather different from

that used by Soviet soil scientists (Section 111, F).

In the classification of the bogs of Ireland, Barry (1954) stated that

two great natural types of bogs occur. The first type comprises the

Raised Bogs of the central plains; and the second, the Blanket Bogs

of the west. To the latter is added the subtype High Level Blanket Bogs.

The Raised Bogs, a term synonymous with high moor, average 25 feet

in thickness. The Blanket Bogs, which occur on gently to strongly sloping

topography, average 8 feet in thickness. This latter class has some features

similar to Weber’s (1903) low moor.

In a study of surface patterns in boreal peatlands, Sjors (1961)

recognized two groups, namely patterns occurring in peatland areas

without permafrost, and patterns occurring in peatland areas with

permafrost. He further subdivided each of these classes into groups

based on source of nutrients, ombrotrophic and minerotrophic. The

ombrotrophic group receives nutrients from the air, and the minerotrophic

from the soil.



120



R. S. FARNHAM AND H. R. FINNEY



B. SURFACEVEGETATION

Ogg (1939) divided the peatlands of England into four categories

based on surface vegetation, namely fen, carr, moor, and heath. Plants

occurring on the fen are mostly sedges and grasses, on the carr mostly

trees and shrubs, on the heath mostly heather, and on the moor mostly

Sphagnum mosses and cotton grass.

Radforth (1952, 1953) devised a scheme for classifying “organic

terrain” (peatland) in Canada. This scheme was assembled because of

problems associated with trafficability, construction, and foundation

TABLE I

Summary of Properties Designating Nine Pure Coverage Classesa

~~



Stature

(approx.

height)



Texture

(where .

required)



Woody



15 ft. or over



-



Woody



5 to 15 ft.



-



Nonwoody



2 to 5 ft.



-



Woody



2 to 5 ft.



-



Woody



0 to 2 ft.



-



Nonwoody



0 to 2 ft.



-



Nonwoody



0 to 2 ft.



-



Nonwoody



0 to 4 in.



Leathery to

crisp



Nonwoody



0 to 4 in.



Soft or

velvety



Coverage Woodiness vs.

type nonwoodiness



~



a



From Radforth (1952).



Growth

habit

Tree form

Young or

dwarfed,

tree or

bush

Tall grasslike

Tall shrub

or very

dwarfed

tree

Low

shrub

Mats,

clumps, or

patches,

sometimes

touching

Singly

or loose

association

Mostly

continuous

mats

Often

continuous

mats, sometimes in

hummocks



Example

Spruce,

larch

Spruce,

larch,

willow,

birch

Grasses

Willow,

birch,

Labrador

tea

Blueberry,

laurel

Sedges,

grasses



Orchid,

pitcher

plant

Lichens



Mosses



CLASSIFICATION OF ORGANIC SOILS



121



engineering on organic terrain. His system has nine coverage classes

based on quality of vegetation (Table I ) which includes woody nature

of vegetation, height, texture of vegetation, and growth habit. The “organic terrain” is further characterized by subsurface (upper 6 inches)

features of the peat as indicated by pollen analysis, topographical features, and Munsell color designation of aerial photograph tone. Radforth

(1955,1958) has developed means of determining and mapping coverage

classes by aerial photograph interpretation.

In studies of the peatlands occupying the eastern extent of glacial

Lake Agassiz in Minnesota, Heinselman ( 1963) presented a classification

based on ( 1 ) water movement pattern, ( 2 ) physical features of the

peatland itself, ( 3 ) peat characteristics, and ( 4 ) natural vegetation.

However, the differentiating features of his classes are essentially vegetation; the kind of plants, density, and pattern, and the other differentiating

features are inferred from the vegetation. His types are:



1. Mineral-influenced (soligenous ) swamp

2. Transitional bog

3. Weakly soligenous poor bog

4. Muskeg ( semiombrogenous “mosses”)

5. String bog (strangmoor)

6. String bog and island complex

7. Poor fens and treeless bogs lacking strange

8. Disturbed peatlands

C. CHEMICAL

PROPERTIES

Either measured or inferred chemical properties have been used as

criteria of classification. Sukachev (1926) classified Soviet bogs into two

broad types : ground-nourished bogs and atmospherically nourished bogs.

The ground-nourished bogs include the low moors of the grassy, hypnoid,

and forest types; transition bogs of the grassy intermediary and forest

intermediary types. Atmospherically nourished bogs comprise the high

moors composed of mosses, mostly Sphagnum.

In Minnesota, Alway (1920) grouped organic soils into high-lime and

low-lime types on the basis of their need for lime application. The highlime type did not respond to lime, but the low-lime type did, On the

basis of pH, Harmer (1941) classified organic soils into three groups,

namely ( 1 ) low-lime with pH of 4.5 or less, high-lime with pH of 7.0

to 4.6, and alkaline with pH of 7.1 or higher. Nygard (1954) classified

organic soils into lime-sufficient and lime-deficient types. The lime-s&cient soils contained 1.2 per cent or more CaO, whereas the lime-deficient

group contained less than 0.6 per cent CaO. He further stated that low



122



R. S. FARNHAM AND H. R. FINNEY



pH values, 4.5 or below, were not reliable indicators of lime deficiency,

but lime content was a completely reliable indicator. Furthermore, in

his Minnesota studies, he found that no reliable bog indicator plants

existed for lime deficiency.

Along the same approach, Godwin (1941) proposed the following

scheme for the classification of Britain’s bogs:

I. Topogenous mires or fens

A. Eutrophic fen

B. Oligotrophic fen

11. Ombrogenous mires

A. Blanket bogs

B. Raised bogs



D. BOTANICAL

ORIGIN

One of the more influential early workers in peat studies was Post

(19243).He stated that the following points must be considered in studying and classifying organic soils:

1. Definition of both macro- and microbotanical properties

2. Degree of humidity (wetness) during formation

3. Nutrients available to plants growing in peat bogs

4. Nature of decomposition processes

5. Deposition of peat, formed in place or transported in

6. Structural properties must be defined

He is perhaps most famous for his scheme of determining the extent

of decomposition. This was expressed by the symbol H. Thus little-decomposed, fibrous, light-colored peat was defined as HI, whereas well

decomposed, colloidal, dark-colored material was Hlo. R was used to

designate the presence of root fibers (scale 0-3); V, wood residues

(0-3); and B, the degree of moisture (0-3).

In classifying the peats of Finland (Kivinen, 1954), botanical composition is the first consideration. The degree of decomposition of each

of the classes is then rated according to Post’s scale. The higher categories

in the Finnish scheme follow:

Botanical origin



Main group



Moss (or Sphagnum) peat

Carex moss peat

Wood moss peat



Moss peat



Moss carex peat

Eutrophic moss carex peat

Wood carex peat

Carex peat

Bryales carex peat



Fen peat



CLASSIFICATION OF ORGANIC SOILS



123



Several American workers have used botanical origin as a basis of

organic soil classification. J. H. Davis (1946) in studies of Florida peats,

Rigg (1958) in studies of Washington peats, and J. F. Davis and Lucas

(1959) in discussing Michigan’s organic soils, for example, used this

criterion as the basis of taxa at the highest category. The lowest category was the established soil series. Incidentally, botanical origin is perhaps the most widely used criterion in organic soil classification.



E. MORPHOLOGY

Few schemes based exclusively on morphological properties have

been devised. However, one might argue that schemes based on botanical

origin essentially reflect morphology. This may be correct when the peat

is only slightly decomposed, but, for example, when an organic horizon

is indicated as moss peat, Post H7, a bias exists. That is to say that the

finely divided matrix may or may not have arisen from moss. In a key

to soils of Michigan, Veatch (1953) subdivided organic soils in the

following manner:

I. Organic matter, more advanced stage of decomposition

A. Highest organic matter content

B. High proportion of admixed mineral matter

11. Organic matter, less advanced stage of decomposition

A. Highest organic matter content

B. Admixed organic and inorganic matter



The lowest categories comprised 12 soil series.

Dachnowski-Stokes ( 1940) emphasized the importance of structure as

a morphological feature of organic soils. Four main kinds of structural

units were observed, namely ( 1 ) horizontal, ( 2 ) vertical, ( 3 ) fragmental

or blocky, and (4)granular.

One of the most comprehensive systems of describing organic soil

horizons was presented by Troels-Smith (1955), a Danish worker. He

considered three features: ( 1) physical features (appearance and mechanical qualities); ( 2 ) humicity (degree of decomposition); and ( 3 )

component parts. Most of the features were rated on a 5-point scale, 0

indicating a lack of the feature and 4 indicating maximum expression of

that feature. Under physical properties he considered the following

features:

1. Degree of darkness; 0, white, to 4,black

2. Degree of stratification: 0, breaks with equal ease in all directions,

to 4,very thin layers that split easily

3. Degree of elasticity: 0, plastic clay, to 4, fresh sphagnum

4. Degree of dryness; 0, cleanvater, to 4, air dry



124



R. S. FARNHAM AND H. R. FINNEY



5. Spectral color

6. Structure

7. Boundary: 0, boundary area

0.5 mm.



>



lcm., to 4, boundary area



<



In the consideration of humicity, 0 indicates undecomposed plant material, whereas 4 indicates that plant structure is hardly discernible or

completely absent. In determining component deposit elements, the

following classes are employed (note, the names are Latin derivatives) :



1. Substantia humosa (humous substance consisting of completely

or almost completely disintegrated materials)

2. Turfa (macroscopic plant tissues, further subdivided on kinds

present )

3. Detritus (mostly superterranean parts > 2 mm. further subdivided on kinds present)

4. Limus ( mudlike homogeneous, nonplastic deposits consisting of

particles < O.lmm., further subdivided on kinds present)

5. Argilla (mineral particles < 0.06 mm., further subdivided into

clay and silt size)

6. Grana (mineral particles > 0.06 mm., further subdivided on grain

size)

7. Accessory elements (animal shells, tree roots, artifacts, etc.)

It might be noted that some features are described qualitatively, and

others quantitatively. Also, Troels-Smith devised no classification scheme

for placement of horizons or profiles.



F. GENETIC

PROCESSES

Veatch (1927) stated that an abstract scientific classification of peat

should deal with origin and evolution and should have a geologicalbotanical basis. He proposed four “great classes” of soils: ( 1 ) Communizems (common mineral soils); ( 2 ) Lithozems (indurated rock soils);

( 3 ) Hydrozems (water soils); and ( 4 ) Plantazems (organics with low

specific gravity and great water-holding capacity). The Plantazems were

further subdivided into two classes: ( a ) Old-mature and ( b ) Youngrecent or geologic. Dachnowski ( 1924), Kazakov ( 1953), and Kubiena

(1953) recognized two major divisions of organic soils based on origin,

The first comprised soils that developed in water basins and under conditions of poor drainage; and the second, those that developed on moist

flat land under conditions of a rising or fluctuating water table. Waksman

(1942) used a similar approach. The two classes in his highest category

were ( 1) autochthonous formations or true peat and ( 2 ) allochthonous

peats or sedimentary formation.



125



CLASSIFICATION OF ORGANIC SOILS



Auer (1930); a worker who investigated many bogs in Canada, indicated that materials composing the peat bogs may be classified according

to origin and botanical composition. The classes comprising his highest

categories reflect both of these criteria. His eight classes are: ( 1 ) inorganic ooze, ( 2 ) organic ooze (limnetic), ( 3 ) limy ooze (limnetic),

( 4 ) jellylike ooze (limnetic), (5) Carex peat, ( 6 ) Amblystegium peat

TABLE I1

A Sample of U.S.S.R. Soil Classification Schemea

Class V. Taiga forested nnn-podzolized and podzolized soils

Boreal soil formation-short growing season, long cryogenic

period, slowed down siallific weathering

Continental type

Automorphic

of soil formation Leaching out

water regime,

fulvic mobile

humus



Semihydromorphic

Half-boggy water

regime with longlasting seasonally

frozen layer



Subclass 2



Type 1

Podzolic soils



Type 3

Podzolic halfboggy soils



Biogenic soils



Type 2

Gray forest



Type 4

Gray forest

gley soils



Subclass 2

Biolithogenic

soils



Type 5

Demo carbonatic

soil



Type 6

Demo gley

saturated soils



Subclass 3

Biohydrogenic

soils

a



Hydromorphic

Boggy water

regime with longlasting seasonally

frozen layer



Type 7

Boggy low moor

saturated soils

Type 8

Boggy high moor

soils



From Ivanova and Rozov ( 1980).



(telmatic), ( 7 ) Sphagnum peat, and ( 8 ) grass-herb-forest peat (terrestrial).

A Scottish peat worker, Fraser (1943, 1954) indicated that the genetical or developmental relationships of objects of classification become

more important than primary morphological properties. His classification

uses the following categories in the upper levels:

I. Climatic or Zonal Bogs

A. Bogs of cool temperate regions formed under maritime

rainfall at lower elevations-blanket bogs

B. Peat bogs of hill and mountain masses developed under

high rainfall and low temperature, particularly on high

plateaus-hill peat

C. Sub-arctic climatic bogs of tundra regions

D. Arctic-alpine climatic bogs of some alpine plateaus



126



R. S . FARNHAM AND H. R. FINNEY



11. Intrazonal Bogs

A. Peat developing in or on free water

1. Lake basin peat, basal deposition

2. Shallow lakes with swamp vegetation basal deposits

B. Peat developing on water-logged or intermittently flooded

mineral soil and vegetation

1. Valley bog

2. Flush bog



According to Ivanova and Rozov (1960), the latest scheme of soil

classification in the U.S.S.R. envisages the unification of 75 genetic types

occurring in that country into 12 classes. An example of a portion of

this scheme is shown in Table 11. A total of 14 genetic types of organic

soils occur in the scheme.

Pons (1960) has proposed a classification for the Netherlands that

places special emphasis on changes occurring in peat soils after drainage

(Table 111). A molded organic Al is a layer more than 15 cm. thick conTABLE I11

Classification of Organic Soils in the Netherlandsa



1. Organic soils



0



11. Soils with prominent

molded (organic) A,



111. Soils with a moder A,

and an organic B

112. Other soils with a

moder A,

113. Soils with a mull A,



12. Other soils



121. Physically “unripe”

soils

122. Other soils with an

organic B

123. Other soils



From Pons ( 1960).



taining less than 15 per cent original peat particles. A mull A, developed

in an eutrophic molding environment, whereas a moder Al developed in

an oligotrophic molding environment. An organic B horizon is at least

5 cm. thick, occurs within a depth of 120 cm. from the surface, and contains dispersed humus that has moved down from upper horizons. It

occurs mainly in oligotrophic peats.



G. SUMMARY

Some summarizing statements concerning this section are perhaps

in order. One of the more disturbing features of this review is that of

ambiguous terminology. That is, some workers have used or inferred

similar criteria, but have used different terms to indicate them. Then

the fact that many terms have not been quantitatively defined allows

them to be used to describe a wide range of conditions. Another short-



CLASSIFICATION OF ORGANIC SOILS



127



coming is the failure of the classifiers to get at the basic morphology of

organic soils in a quantitative manner. It is the opinion of the writers

that few if any shortcuts exist for determining the characteristics of

organic soils. For example, inferring the characteristics of an organic

horizon by determining the kind of pollen occurring in it, just does not

get at the problem at hand,

In a general review of organic soils, Dawson (1956) summarizes important shortcomings in organic soil classification. He states that a taxonomic system of classifying peat soils that clearly brings out the similarities as well as the differences between these soils is needed. Also, the

present system being used in the U.S. soil survey does less than is needed.

He further indicates difficulties inherent in the present system. First, too

much emphasis is placed on surface layers, which are the layers most

subject to change. Secondly, such sediments as sedimentary peat and

gyttja have been described as muck, or mucky peat, yet they are not

actually highly decomposed. Finally, a system of organic soil classification

should be based on kinds of soil organic materials, and the sequence of

these materials that occur.

In the authors’ opinion, the most significant fault of most of the classification schemes is their failure to provide taxa, especially in the lower

categories that lend themselves to mapping. Seemingly, derivable mapping or cartographic units have not been considered in some schemes.

They are essentially theoretical taxonomic schemes that have little value

in making accurate maps of important land resources. Finally, for a classification scheme to be actually meaningful, it must be tested in the

field by mapping. Then the question is, how many of the schemes have

been tested in this fashion?

IV. Properties of Organic Soils



In this section certain properties that seem presently most useful as

criteria in classification and characterization are considered. They are,

generally, properties that can be rather easily determined, yet inferences

derivable from them may have significant implications in terms of

genesis and use and management. Unfamiliar terminology of organic

soils used in this section is defined in Sections V and VI.



A. PHYSICAL PROPERTIES

Three physical properties, namely water relationships, bulk densities,

and fiber characteristics are considered in this section. Although water

relationships are not diagnostic in the proposed classification scheme,

they are such an important characteristic of organic soils that a section

is devoted to them.



128



R. S . FARNHAM AND H. R. FINNEY



1 . Water Relationships

The various means of determining the water contents of organic soils

as well as the variation in these characteristics among the different kinds

of organic soils have given data with quite different orders of magnitude.

To emphasize these points, data by three different methods and approaches will be considered. Based on the descriptions provided by these

workers, the data presented below would be for fibric, mesic, and sapric

horizons in the proposed system (see Section V ) . Data from Feustel and

Byers (1936) are presented in Table IV. The maximum moisture-holdTABLE IV

The Comparative Water-Absorbing and Water-Retaining Capacities

of Three Organic Soil Horizonsa



Kind of

organic

soil

horizon

Fibric

( Sphagno

Mesic

SaDric

a



Water

required

Water

for

required

moisture

to saturate

equivalent

100 cm3 of

of100 cm3

dry material dry material



Maximum

moistureholding

capacity



Moisture

equivalent



(%I



(%I



(g.)



(n.1



(a.1



1057

374

289



166

112

110



101

91

99



16

27

38



11

27

39



Weight

100 cms

dry

material



From Feustel and Byers (1936).



ing capacity of the three peats shows an appreciable range of values.

In fact, values as high as 3000 per cent have been recorded for fibric

horizons (the maximum moisture or water-holding capacity is the amount

of water the soil retains against gravity, based on the oven dry weight).

Another determination was the moisture equivalent. It is determined by

placing the wet soil in a perforated box and centrifuging at lo00 times

gravity for 40 minutes. The range in moisture equivalent values is much

les than the values of maximum moisture-holding capacity. Also, the

difference between the amount of water required to saturate the dry peat

and the amount required for the moisture equivalent is much greater

for the fibric and least for the sapric. The bulk density values were derived from a standard packing procedure and they, thus, do not represent

values as they occur in the field.

Dyal (1960) reported that pressure plate and pressure membrane

procedures as used in mineral soils, satisfactorily measure water retention

properties of organic soils (Table V). His data emphasize the fact that

fibric horizons release a much greater amount of water at low suctions



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