2:1 to 2:1:1 clay minerals are the main components of clay
minerals, leading to the presence of exchangeable Al
3+ under
base-unsaturated conditions. Soil showing the unique properties
of Andosols and containing almost no allophane was formerly
reported by Uchiyama et al. (1960) and Kato (1962). The report
by Shoji and Ono (1978) of non-allophanic Andosols in the
Tohoku region in Japan became the driving force for modifying
the central property of Andosols in the domestic and worldwide
soil classification systems. The origin of the 2:1 to 2:1:1 clay
minerals which are the main clay mineral components of
non-allophanic Andosols is considered to be aeolian dust from
inland China (Inoue 1981), the alteration of volcanic glass by
weathering, and secondary deposition after hydrothermal alteration in a closed environment. Aeolian dust contains fine-grained
quartz as well as 2:1 clay minerals. Based on the oxygen isotope
ratio of fine quartz in Japanese Andosols, the 2:1 clay minerals in
Andosols are assumed to be derived from aeolian dust from the
drylands of inland China (Mizota et al. 1991).
4.3.2 Classification of Andosols and Related
Soils
(1) Outline of Andosols in the Soil Classification System
of Japan
In Japan, several soil classification systems are used, such as
the Classification of Cultivated Soils in Japan (1995) for
arable land soil and the Classification of Forest Soils in
Japan (1976) for forest soil. This section will explain the
position of Andosols in the up-to-date soil classification
system (The Fifth Committee for Soil Classification and
Nomenclature 2017), which does not depend on land use
type. This classification system includes three categories—
10 great groups, 26 groups, and 120 subgroups—and adopts
a “key-out” system by using diagnostic horizons and characteristics, and places emphasis on compatibility with the
WRB soil classification system.
For the great groups and groups, soils having distinctive
characteristics and soils whose locations are easily specified
due to the significant effect of specific soil-forming factor are
keyed out earlier. Diagnostic horizons and characteristics are
defined using distinctive characteristics and properties that
can greatly affect crop productivity, and based on this, the
unique soils are keyed out. Andosols are keyed out as the
third great group, after Human-made soils, which are
strongly influenced by humans and do not occur naturally,
and Organic soils affected by water.
The central concept of an Andosol is a soil whose main
parent material is volcanic ejecta and is weathered to some
degree or a soil where large amounts of active Al and/or Fe,
which are highly reactive with phosphate, are produced by
in situ weathering. According to the Soil Classification System of Japan (The Fifth Committee for Soil Classification and
Nomenclature 2017) or Comprehensive Soil Classification
System (Obara et al. 2011), Andosols are soils that have a
layer of 25 cm or more in thickness within 50 cm of the soil
surface that has regosolic andic soil properties, representing
weak pedogenetic horizontation mainly derived from volcanic ejecta, or that has andic soil properties, representing the
presence of large amounts of active Al and/or Fe.
Regosolic andic soil properties meet all of the following
requirements:
(1) consists of non-weathered volcanic gravel comprising
less than 50% (by area); and
(2) more than 60% (by weight) of the soil consists of
volcanic ejecta (volcanic ash, pumice, scoria, etc.); and
(3) has a phosphate absorption coefficient of between 3.00
and 15.0 mg P 2 O 5 /g (phosphate retention of at least 25%
but less than 85%, or Al plus 1/2 Fe content (by acid
ammonium oxalate) of at least 0.4% but less than 2.0%)
or an organic carbon content of 3% or more if the phosphate absorption coefficient is less than 3.00 mg P 2 O 5 /g
(phosphate retention of less than 25%, or Al plus 1/2 Fe
content (by acid ammonium oxalate) of less than 0.4%).
Andic soil properties meet all of the following
requirements:
(1) a phosphate absorption coefficient of 15.0 mg P 2 O 5 /g or
more (phosphate retention of 85% or more, or Al plus
1/2 Fe content (by acid ammonium oxalate) of 2.0% or
more); and
(2) a fiber content of less than one sixth of the original
volume after rubbing.
In this classification system, the following soil groups are
defined: “Podzolic Andosols,” representing Podzols derived
from volcanic ash (Fig. 4.14); “Regosolic Andosols,” representing poorly weathered soils derived from volcanic ash
(Fig. 4.15); “Gleyed Andosols,” having gleyic properties;
“Wet Andosols,” having a groundwater–gley property
(Fig. 4.16); “non-allophanic Andosols,” representing acidic
soils without allophanic minerals (Fig. 4.17); and “Allophanic Andosols,” representing typical Andosols (Fig. 4.18).
(2) Classification of Podzols derived from volcanic ash
The pedogenetic soil formation process of Andosols is
essentially different from that of Podzols. Andosols are
formed by andosolization—the in situ formation of
short-range-order minerals and/or Al(Fe)–humus complexes;
Podzols are formed by podzolization—the formation of
4 Major Soil Types
85
minerals, leading to the presence of exchangeable Al
3+ under
base-unsaturated conditions. Soil showing the unique properties
of Andosols and containing almost no allophane was formerly
reported by Uchiyama et al. (1960) and Kato (1962). The report
by Shoji and Ono (1978) of non-allophanic Andosols in the
Tohoku region in Japan became the driving force for modifying
the central property of Andosols in the domestic and worldwide
soil classification systems. The origin of the 2:1 to 2:1:1 clay
minerals which are the main clay mineral components of
non-allophanic Andosols is considered to be aeolian dust from
inland China (Inoue 1981), the alteration of volcanic glass by
weathering, and secondary deposition after hydrothermal alteration in a closed environment. Aeolian dust contains fine-grained
quartz as well as 2:1 clay minerals. Based on the oxygen isotope
ratio of fine quartz in Japanese Andosols, the 2:1 clay minerals in
Andosols are assumed to be derived from aeolian dust from the
drylands of inland China (Mizota et al. 1991).
4.3.2 Classification of Andosols and Related
Soils
(1) Outline of Andosols in the Soil Classification System
of Japan
In Japan, several soil classification systems are used, such as
the Classification of Cultivated Soils in Japan (1995) for
arable land soil and the Classification of Forest Soils in
Japan (1976) for forest soil. This section will explain the
position of Andosols in the up-to-date soil classification
system (The Fifth Committee for Soil Classification and
Nomenclature 2017), which does not depend on land use
type. This classification system includes three categories—
10 great groups, 26 groups, and 120 subgroups—and adopts
a “key-out” system by using diagnostic horizons and characteristics, and places emphasis on compatibility with the
WRB soil classification system.
For the great groups and groups, soils having distinctive
characteristics and soils whose locations are easily specified
due to the significant effect of specific soil-forming factor are
keyed out earlier. Diagnostic horizons and characteristics are
defined using distinctive characteristics and properties that
can greatly affect crop productivity, and based on this, the
unique soils are keyed out. Andosols are keyed out as the
third great group, after Human-made soils, which are
strongly influenced by humans and do not occur naturally,
and Organic soils affected by water.
The central concept of an Andosol is a soil whose main
parent material is volcanic ejecta and is weathered to some
degree or a soil where large amounts of active Al and/or Fe,
which are highly reactive with phosphate, are produced by
in situ weathering. According to the Soil Classification System of Japan (The Fifth Committee for Soil Classification and
Nomenclature 2017) or Comprehensive Soil Classification
System (Obara et al. 2011), Andosols are soils that have a
layer of 25 cm or more in thickness within 50 cm of the soil
surface that has regosolic andic soil properties, representing
weak pedogenetic horizontation mainly derived from volcanic ejecta, or that has andic soil properties, representing the
presence of large amounts of active Al and/or Fe.
Regosolic andic soil properties meet all of the following
requirements:
(1) consists of non-weathered volcanic gravel comprising
less than 50% (by area); and
(2) more than 60% (by weight) of the soil consists of
volcanic ejecta (volcanic ash, pumice, scoria, etc.); and
(3) has a phosphate absorption coefficient of between 3.00
and 15.0 mg P 2 O 5 /g (phosphate retention of at least 25%
but less than 85%, or Al plus 1/2 Fe content (by acid
ammonium oxalate) of at least 0.4% but less than 2.0%)
or an organic carbon content of 3% or more if the phosphate absorption coefficient is less than 3.00 mg P 2 O 5 /g
(phosphate retention of less than 25%, or Al plus 1/2 Fe
content (by acid ammonium oxalate) of less than 0.4%).
Andic soil properties meet all of the following
requirements:
(1) a phosphate absorption coefficient of 15.0 mg P 2 O 5 /g or
more (phosphate retention of 85% or more, or Al plus
1/2 Fe content (by acid ammonium oxalate) of 2.0% or
more); and
(2) a fiber content of less than one sixth of the original
volume after rubbing.
In this classification system, the following soil groups are
defined: “Podzolic Andosols,” representing Podzols derived
from volcanic ash (Fig. 4.14); “Regosolic Andosols,” representing poorly weathered soils derived from volcanic ash
(Fig. 4.15); “Gleyed Andosols,” having gleyic properties;
“Wet Andosols,” having a groundwater–gley property
(Fig. 4.16); “non-allophanic Andosols,” representing acidic
soils without allophanic minerals (Fig. 4.17); and “Allophanic Andosols,” representing typical Andosols (Fig. 4.18).
(2) Classification of Podzols derived from volcanic ash
The pedogenetic soil formation process of Andosols is
essentially different from that of Podzols. Andosols are
formed by andosolization—the in situ formation of
short-range-order minerals and/or Al(Fe)–humus complexes;
Podzols are formed by podzolization—the formation of
4 Major Soil Types
85