SOIL ATLAS OF ASIA 2ND EDITORIAL BOARD MEETING RURAL DEVELOPMENT ADMINISTRATION, NATIONAL INSTITUTE OF AGRICULTURAL SCIENCES, JEONJU, REPUBLIC OF KOREA | 29 APRIL – 3 MAY 2019

1. Before
classification:
PROFILE
DESCRIPTION!!!

2. The capital letters like H, O, A, E, B, C and R represent the
master horizons and layers of soils.
The capital letters are the base symbols to which other
characters are added to complete the designation (i.e.
2Btg1).
Most are genetic soil horizons, reflecting a qualitative
judgement about the kind of changes which have taken
place.
Genetic horizons are not equivalent to diagnostic
horizons, although they may be identical in soil profiles.
Diagnostic horizons are quantitatively defined features
used in classification.
MASTER HORIZONS AND LAYERS

3. Code Determination
Mineral horizons
A Surface or near-surface mineral horizon with some organic accumulation, usually a darker
colour than underlying horizons and/or smaller clay content than underlying horizons.
E A near-surface mineral horizon characterized by a loss of clay, iron, aluminium, or some
combination of these; usually lighter in color (higher value and/or lower chroma) than the
overlying A and underlying B.
B A mineral horizon characterised by one or more of the following: a concentration of clay, iron,
aluminium, organic material or several of these; a structure and/or consistence unlike the
horizons above and below; stronger colours (higher chroma and/or redder hue) than the
horizons above and below.
C Consolidated or unconsolidated material, usually partly weathered, little affected by pedogenic
processes.
R Hard bedrock that cannot be cut with a spade.
Organic horizons
O Horizons dominated by organic material consisting of undecomposed organic materials that
have accumulated on the surface of either mineral or organic soils. O horizons are not saturated
with water for prolonged periods.
H These horizons dominated by organic material formed from accumulations of undecomposed or
partially decomposed organic material. All H horizons are saturated with water for prolonged
periods, or were once saturated but are now drained artificially.
MASTER HORIZONS AND LAYERS
full list in FAO book page 67

4. Suffix Short description Used for
b Buried genetic horizon mineral horizons
c Concretions or nodules mineral horizons
g* Stagnic conditions / *USA strong gley no restriction
h Illuvial accumulation of organic matter mineral horizons
i/*ss Slickensides / *USA mineral horizons
k Accumulation of pedogenetic carbonates no restriction
l* Capillary fringe mottling (gleying) *only in FAO no restriction
n Pedogenetic accumulation of exchangeable sodium no restriction
p Ploughing or other human disturbance
no restriction
E, B or C as Ap
r* Strong reduction *only in FAO no restriction
t Illuvial accumulation of silicate clay mineral horizons
w Development of colour or structure B horizons
z Pedogenic accumulation of salts more soluble than gypsum no restriction
d Dense layer (physically root restrictive)
x Fragipan characteristics no restriction
Subordinate distinctions
within master horizons
full list FAO book page 72

5. Discontinuities
In mineral soils, Arabic numerals are used
as prefixes to indicate discontinuities.
Numbering starts with the second layer of
contrasting material, which is designated
„2”. Underlying contrasting layers are
numbered consecutively.
Where two or more consecutive horizons
formed in one kind of material, the same
prefix number applies to all of the horizon
designations in that material.
In organic soils, discontinuities between
different kinds of layers are not identified.
A
B
2C
3C
4C
A
B
2C
3Bt
3C

6. Suffix Short description Used for
b Buried genetic horizon mineral horizons
Ap
C
Ab
C
Used in mineral soils to indicate
identifiable buried horizons with
major genetic features that
were formed before burial.
If the buried horizon formed in a
material lithological like that of
the overlying deposit, a number
prefix is not used.

7. Suffix Short description Used for
b Buried genetic horizon mineral horizons
Ap
AB
B
2Ab
2Blb
2Cl
Used in mineral soils to indicate
identifiable buried horizons with
major genetic features that
were formed before burial.
If the material in which a
horizon of a buried soil formed
is lithological unlike that of the
overlying material, the
discontinuity is designated by
number prefixes and the „b”
symbol for a buried horizon is
used as well.

8. Cr
Suffix Short description Used for
r* Strong reduction *only in FAO no restriction
Cr

9. Gleyic colour pattern Stagnic colour pattern
Gleization
A
E
Btg
C
A
Bl
Cr

10. Suffix Short description Used for
l*
Capillary fringe mottling (gleying)
*only in FAO
no restriction
Cl

11. Suffix Short description Used for
g* Stagnic conditions / *USA strong gley no restriction
Bg

12. Bc
Suffix Short description Used for
c Concretions or nodules mineral horizons

13. Bc

14. PAGE 79

15. RULES FOR CLASSIFICATION (three steps)
The expression, thickness and depth of layers are checked against the
requirements of WRB diagnostic categories, defined in terms of morphology
and/or analytical criteria.
(overlapping or coinciding possible)
Step 1 – the diagnostics

16. RULES FOR CLASSIFICATION
The combination of diagnostics compared with the WRB Key in order to find the
RSG, which is the first level of WRB classification.
The user should go through the Key systematically!!!!
The soil belongs to the first RSG for which it meets all specified requirements.
Step 2 – the key

17. RULES FOR CLASSIFICATION
For the second level of WRB classification, qualifiers are used.
Step 3 – the qualifiers
Principal qualifiers:
are regarded as being most significant for a further
characterization of soils of the particular RSG.
They are given in a ranked order.
Supplementary qualifiers:
All other qualifiers (further details about the soil).
They are not ranked, but listed alphabetically.

18. Base Saturation
Basic cations=∑ K+,Ca2+, Mg2+, Na+10 cmol (+)/kg
Basic cations
CEC
Base saturation % = x 100
MEASURED IN 1 M NH4OAc (pH 7)
WRB 2006

19. WRB2014/2015
Effective base saturation
Exchangeable (Ca+ Mg + K + Na)
Exchangeable (Ca + Mg+ K + Na)+ Al
exchangeable bases by 1 M NH4OAc (pH 7),
exchangeable Al by 1 M KCl (unbuffered)] of < 50%:

20. A
E
Bt
C
L
A
Y
ARGIC ARGIC
ARGIC ARGIC
CEC / kg clay
≥ 24 cmol+
CEC / kg clay
≥ 24 cmol+
CEC / kg clay
< 24 cmol+
CEC / kg clay
< 24 cmol+
eB ≥ 50 %
eB ≥ 50 %
eB < 50 %
eB < 50 %
Luvisol Alisols
Lixisols Acrisols
In major part
between
50-100 cm