Changing concepts in soil classification. The structure of

Szent István
U n i v e rs i t y
Erika Michéli
H u n g a r y

Changing concepts
in soil classification

Unlike plants and animals
soil is a continuum

1927

As classification is result
of human thinking
It reflects the current knowledge and need

Most soil classification schemes developed on
genetic basis

Vasili Dokuchaev
The Russian School
Soil forming factors
Soil forming processes
Different Soils

Mendelejev Dokuchaev
Sibirtsev Glinka
The Russian School

Hans Jenny:
Factors of soil formation
(1941)
S = ƒ (cl, o, r, p, t..)
(climate, organisms, topography, parent material, time) time

Guy Smiths
‘‘The processes that go on can rarely be observed or measured. Nevertheless, the
genesis of soils is extremely important both to the taxonomy of soils and to the mapping
in the field. Genesis is important to the classification partly because it produces the
observable or measureable differences that can be used as differentiae. Genesis does
not appear in the definitions of the taxa but lies behind them.’’

In 1952 G. Smith presented his diagnostic approach in Belgium
“time zero of modern soil classification”

Richard Arnold Peter Schad
“Soil processes are poorly understood……
Soil properties result from soil processes and are more
readily quantifiable than soil processes”

Atkár

Soil processes are poorly understood, and
specific pedogenic processes occur simultaneously
in a given soil, reinforcing or contradicting one
another.
It is also assumed that polygenesis likely has
occurred in most, if not all soils, making genetic
interpretations difficult.
Soil properties result from soil processes and
are more readily quantifiable than soil
processes.

Starting with the ‘‘Seventh Approximation’’, 1960
and culminating with Soil Taxonomy, 1975
(Soil Survey Staff, USDA) soils were classified with
quantitative properties, particularly morphological
properties, delineated as diagnostic horizons and
properties.
Soil-forming processes were de-emphasized and kept
in the background.

soil-forming factors
↓
soil-forming processes
↓
diagnostic horizons, properties, materials
↓
soil taxonomic system

A similar approach was used by the
FAO-UNESCO system (1974), (1988)
World Reference Base for Soil Resources WRB, 1998
and are used in most new national systems (Russian,
Check, Chinese, etc.)

World Soil Resources Reports 84
1988
WORLD REFERENCE BASE FOR
SOIL RESOURCES
RUSSIAN SOIL
CLASSIFICATION
SYSTEM
Moscow
2001

History of WRB (1)
In the past decades there has been an increased
interest in soil information for global environmental
studies.
The 20 year old, but still the only available
harmonized global soil map, the FAO-UNESCO
Soil Map of the World (1:5 M), is based on
information collected thirty or more years ago.

History of WRB (2)
The original FAO Map legend ( FAO, 1974) was
based on diagnostic horizons and properties
borrowed from USDA Soil Taxonomy
26 Major Soil Units, 152 Soil Units
Revised legends (FAO-Un esco-ISRIC, 1988; 1990)

History of WRB (3)
Based on conclusions of several meetings
international agreement on major soil groups, and
common language was necessary.
WRB , World Reference Base for Soil Resources
– based on the FAO Revised legend
– new pedological, ecological knowledge incorporated
(World Reference Base for Soil Resources, FAO/ISRIC/ISSS, 1998)

WRB is designed as…
an easy means of communication among scientists to
identify, characterize and name major types of soils.
It is not meant to replace national soil classification
systems, but be a tool for better correlation between
national systems.
It aims to help in improving national systems

History of WRB (4)
In 1998 the Internationa l Union of Soil Science
endorsed the WRB as the recommended soil
correlation system for all soil scientists.
The European Commission selected WRB as
correlation scheme for harmonized soil maps and
databases for Europe.

The 1 st official maps published with WRB units (1)
Soil Digital Data Base
for Europe, 1:1 M

The 1 st official maps published with WRB units (2)

Current structure and principles
The taxonomic units of the WRB are based on
diagnostic (reference) horizons, soil properties
and/or soil materials.
First level: 30 Reference Soil Groups (defined by
key)
Lower level (s) are defined by set of prefixes as
unique qualifiers added to the reference soil
groups.

Current structure and principles…cont
Qualifiers are listed in priority sequence for each
reference soil groups.
Two qualifiers may be used in soil unit names.
If additional qualifiers are needed, those follow
the Reference Soil Group name between brackets.
e.g.: Sapri-cryic Histosol (Dystric)

Histic or Folic horizon > 40 cm deep
↓no
Cryic horizon
↓ no
Human modifications
↓ no
Depth < 25 cm
↓ no
> 35% clay, vertic horizon
↓ no
Fluvic materials
↓ no
Salic horizon
↓ no
Gleyic properties
↓ no
Andic or vitric horizon
↓ no
Spodic horizon
yes
→
yes
→
yes
→
yes
→
yes
→
yes
→
yes
→
yes
→
yes
→
yes
→
HISTOSOLS
CRYOSOLS
ANTHROSOLS
LEPTOSOLS
VERTISOLS
FLUVISOLS
SOLONCHAKS
GLEYSOLS
ANDOSOLS
PODZOLS

World Reference Base for Soil Resources
HISTOSOLS
CRYOSOLS
ANTHROSOLS
LEPTOSOLS
VERTISOLS
FLUVISOLS
SOLONCHAKS
GLEYSOLS
ANDOSOLS
PODZOLS
PLINTHOSOLS
FERRALSOLS
SOLONETZ
PLANOSOLS
CHERNOZEMS
KASTANOZEMS
PHAEOZEMS
GYPSISOLS
DURISOLS
CALCISOLS
ALBELUVISOLS
ALISOLS
NITISOLS
ACRISOLS
LUVISOLS
LIXISOLS
UMBRISOLS
CAMBISOLS
ARENOSOLS
REGOSOLS

EXAMPLE
Velence
Diagnostics
Mollic horizon
Cambic horizon
Calcic horizon
Based on
the key
Chernozems

Chernic
Vertic
Gleyic
Luvic
Glossic
Calcic
Siltic
Vermic
Haplic
A Chernozems referenciacsoport minősítői
(qualifiers) prioritási sorrendben
CHERNOZEMS
Silti-
Calcic Chernozem (Vermic)

Major points of debate
Disagreements on definitions of diagnostic
categories
Terminology questions
Listing / ranking of qualifiers?
(“strong expression qualifiers’, “intergrade
qualifiers”, “secondary characteristics qualifiers”)
How many qualifiers (levels)?

The WRB publications :
World Reference Base for Soil Resources: Introduction
(Working Group RB,1998a);
World Reference Base for Soil Resources: Atlas
(Working Group RB, 1998b);
World Reference Base for Soil
Resources:(FAO/ISRIC/ISSS, 1998).
http://www.fao.org/ag/agl/agll/wrb

Soil Reference Groups of WRB (and
related diagnostic criteria)
Discussion of Reference Groups will be based on the
FAO World Soil Resources Report # 94
“LECTURE NOTES ON THE MAJOR SOILS OF THE WORLD”
available also:
http://www.
http:// www.fao fao.org/ .org/ag ag/agl agl/agll agll/wrb wrb/

The 30 Reference Soil Groups are aggregated
in 10 ‘sets’ on the basis of 'dominant
identifiers', i.e. those soil forming factor(s)
which most clearly influenced soil formation.

SET # 1
Organic soils. Soils with more than a
defined quantity of 'organic soil materials'.
Reference Soil Group: the HISTOSOLS.

SET # 2
Soils of set # 2 vary widely in properties
and appearance and can occur in any
environment but have in common that their
properties are strongly affected by
human activity.
Reference Soil Group: ANTHROSOLS.

SET #3
Mineral soils whose formation is conditioned by the
particular properties of their parent material.
Reference Soil Groups (3)
ANDOSOLS of volcanic regions
the sandy ARENOSOLS
the swelling and shrinking heavy clayey
VERTISOLS

SET #4
Mineral soils whose formation was influenced mainly by
their topographic/physiographic setting.
Reference Soil Groups (4):
In low terrain positions:
Young alluvial FLUVISOLS, which show stratification recent
sedimentation
Non-stratified GLEYSOLS in waterlogged areas.
In elevated and/or eroding areas:
Shallow LEPTOSOLS over hard rock or highly calcareous
material,
Deeper REGOSOLS, which occur in unconsolidated materials.

SET #4

SET # 5
Soils that are only moderately developed on
account of their limited pedogenetic age or
because of rejuvenation of the soil material.
They have not more in common than 'signs of
beginning soil formation'
Reference Soil Group: the CAMBISOLS.

SET #6
Red and yellow soils of wet tropical and subtropical
regions.
PLINTHOSOLS on old weathering surfaces with ‘plinthite’
deeply weathered FERRALSOLS that have a very low cation
exchange capacity
ALISOLS with high cation exchange capacity and much
exchangeable aluminium,
deep NITISOLS in relatively rich parent material
strongly leached, red and yell ow ACRISOLS on acid parent
rock
LIXISOLS with a low cation exchange capacity but high
base saturation percentage.

SET #7
Soils in arid and semi-arid regions..
Soluble salts may accumulate at some depth or, in
areas with shallow ground-water, near the soil
surface.
– SOLONCHAKS with a high content of soluble salts,
– SOLONETZ with a high percentage of adsorbed
sodium ions,
– GYPSISOLS with a horizon of secondary gypsum
enrichment,
– DURISOLS with a layer or nodules of soil material
that is cemented by silica, and
– CALCISOLS with secondary carbonate enrichment.

SET #8
soils in the steppe zone
CHERNOZEMS with deep, very dark surface soils and
carbonate enrichment in the subsoil,
KASTANOZEMS with less deep, brownish surface soils
and carbonate and/or gypsum accumulation at some depth
PHAEOZEMS, the dusky red soil s of prairie regions with
high base saturation but no visible signs of secondary
carbonate accumulation.

SET #9
soils of humid temperate regions with evidence of
redistribution of clay and/or or-ga-nic matter.
acid PODZOLS with a bleached eluviation horizon over
an accumula-tion horizon of organic matter with aluminium
and/or iron,
PLANOSOLS with a bleached topsoil over dense, slowly
permeable subsoil,
base-poor ALBELUVISOLS with a bleached eluviation
horizon tonguing into a clay-enriched subsurface horizon,
base-rich LUVISOLS with a distinct clay accumulation
horizon, and
UMBRISOLS with a thick, dark, acid surface horizon that
is rich in organic matter.

SET #10
CRYOSOLS - Soils formed in a permafrost
environment.