3.1.2 Latest Soil Classification System in Japan
This system defines the following categories: soil great
group, soil group, and soil subgroup, using the key-out rule.
The keys employed are defined as diagnostic horizons,
diagnostic properties, and diagnostic materials that are
determined objectively and quantifiably. Their main characteristics can be summarized as follows.
(1) Diagnostic Horizon
Albic horizon: An eluvial horizon with a light color from
which clay and/or free Fe oxides have been removed.
Albic paddy epipedon: A plowed epipedon in paddy
fields with bleaching.
Anthraquic-gray horizon: A subsurface horizon with
epiaquic properties that has formed under irrigation in paddy
fields. Commonly found in clayey paddy fields with shallow
groundwater.
Anthraquic-iron horizon: A subsurface horizon with Fe
illuviation typically developed in paddy fields with good
percolation of water. Usually accompanied by Mn
illuviation.
Argic horizon: A subsurface horizon with a significantly
higher percentage of clay than the overlying soil material.
Cambic horizon: A subsurface horizon resulting from
physical alterations, chemical transformations, or removals,
or from a combination of two or more of these processes.
Dark Eutric epipedon: A dark-colored epipedon enriched
in bases and organic matter.
Gley horizon: A horizon which is saturated with water for
the majority of the time in normal years and showing a
blue-gray color with the rapid positive dipyridyl reaction.
Humic epipedon: A dark-colored epipedon with high
organic matter content.
Hyperhumic epipedon: A humic epipedon that has particularly high organic matter content.
Paddy epipedon: A plowed epipedon in paddy fields
without bleaching.
Pseudogley horizon: A horizon naturally saturated with
water for some time in a year and under reduced conditions
with epiaquic properties.
Red-Yellow cambic horizon: A cambic horizon with
red-color or yellow-color weathering.
Spodic horizon: A subsurface horizon that has formed as
a result of podsolization. It shows a darker and/or more
reddish color than the underlying horizon due to the presence of organic matter and/or Fe and Al oxides leached from
the overlying horizon.
Thapto-humic horizon: A dark subsurface horizon with
organic matter that was buried by newly deposited materials
such as Fluvic and eolian sediments.
(2) Diagnostic Properties
Andic soil properties: Properties that show low bulk density,
large phosphorus fixation and accumulation of organic
matter due to the presence of active Al typically formed
during weathering of volcanic glass.
Endoaquic properties: Properties that appear when soil is
saturated with groundwater for some time in a year. They are
exclusive from gley properties and show mottles of the
oxidized form of Fe on the surfaces of peds and voids.
Epiaquic properties: Properties that show reduced conditions from saturation with surface water for part of the
year.
Gley properties: Properties that show a blue-gray color
due to the presence of the reduced form of Fe under saturated conditions.
Non-allophanic andic soil properties: Properties characterized by the predominance of 2:1 type clay minerals in
addition to andic soil properties. Active Al is derived from
Al–humus complexes. Soil with non-allophanic andic soil
properties exhibits strong acidity due to the presence of large
amounts of exchangeable Al.
Physical immaturity: Properties that rarely undergo
dehydration process after sediments under water become
land.
Red-Yellow soil properties: Properties that show reddish
or yellowish soil color and low organic matter content due to
the large extent of weathering processes.
Regosolic andic soil properties: Properties that show
weathering of volcanogenous materials and accumulation of
organic matter to some extent.
Thionic soil properties: Properties that exhibit strong
acidity with pale yellow mottles of jarosite. The strong
acidity is a result of the oxidation of lacustrine and marine
sediments containing sulfides.
(3) Diagnostic Materials
Artefacts: Human-made materials that are not naturally
present on the Earth’s surface.
Calcaric sediments: Unconsolidated sediments containing
carbonates equivalent to or more than 40% CaCO 3 .
Fluvic materials: Fluvic, marine, and lacustrine unconsolidated sediments of Holocene age.
Hetero-soil materials: Soil materials classified as a soil
great group other than that of the bulk soil materials.
Organic materials: Materials mainly composed of
decomposed or undecomposed plant litter on the land surface. The materials should contain 20% or more of organic
carbon and should not show andic soil properties.
Peat materials: Materials mainly composed of decomposed or undecomposed plant litter accumulated under
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H. Shinjo and Y. Takata
This system defines the following categories: soil great
group, soil group, and soil subgroup, using the key-out rule.
The keys employed are defined as diagnostic horizons,
diagnostic properties, and diagnostic materials that are
determined objectively and quantifiably. Their main characteristics can be summarized as follows.
(1) Diagnostic Horizon
Albic horizon: An eluvial horizon with a light color from
which clay and/or free Fe oxides have been removed.
Albic paddy epipedon: A plowed epipedon in paddy
fields with bleaching.
Anthraquic-gray horizon: A subsurface horizon with
epiaquic properties that has formed under irrigation in paddy
fields. Commonly found in clayey paddy fields with shallow
groundwater.
Anthraquic-iron horizon: A subsurface horizon with Fe
illuviation typically developed in paddy fields with good
percolation of water. Usually accompanied by Mn
illuviation.
Argic horizon: A subsurface horizon with a significantly
higher percentage of clay than the overlying soil material.
Cambic horizon: A subsurface horizon resulting from
physical alterations, chemical transformations, or removals,
or from a combination of two or more of these processes.
Dark Eutric epipedon: A dark-colored epipedon enriched
in bases and organic matter.
Gley horizon: A horizon which is saturated with water for
the majority of the time in normal years and showing a
blue-gray color with the rapid positive dipyridyl reaction.
Humic epipedon: A dark-colored epipedon with high
organic matter content.
Hyperhumic epipedon: A humic epipedon that has particularly high organic matter content.
Paddy epipedon: A plowed epipedon in paddy fields
without bleaching.
Pseudogley horizon: A horizon naturally saturated with
water for some time in a year and under reduced conditions
with epiaquic properties.
Red-Yellow cambic horizon: A cambic horizon with
red-color or yellow-color weathering.
Spodic horizon: A subsurface horizon that has formed as
a result of podsolization. It shows a darker and/or more
reddish color than the underlying horizon due to the presence of organic matter and/or Fe and Al oxides leached from
the overlying horizon.
Thapto-humic horizon: A dark subsurface horizon with
organic matter that was buried by newly deposited materials
such as Fluvic and eolian sediments.
(2) Diagnostic Properties
Andic soil properties: Properties that show low bulk density,
large phosphorus fixation and accumulation of organic
matter due to the presence of active Al typically formed
during weathering of volcanic glass.
Endoaquic properties: Properties that appear when soil is
saturated with groundwater for some time in a year. They are
exclusive from gley properties and show mottles of the
oxidized form of Fe on the surfaces of peds and voids.
Epiaquic properties: Properties that show reduced conditions from saturation with surface water for part of the
year.
Gley properties: Properties that show a blue-gray color
due to the presence of the reduced form of Fe under saturated conditions.
Non-allophanic andic soil properties: Properties characterized by the predominance of 2:1 type clay minerals in
addition to andic soil properties. Active Al is derived from
Al–humus complexes. Soil with non-allophanic andic soil
properties exhibits strong acidity due to the presence of large
amounts of exchangeable Al.
Physical immaturity: Properties that rarely undergo
dehydration process after sediments under water become
land.
Red-Yellow soil properties: Properties that show reddish
or yellowish soil color and low organic matter content due to
the large extent of weathering processes.
Regosolic andic soil properties: Properties that show
weathering of volcanogenous materials and accumulation of
organic matter to some extent.
Thionic soil properties: Properties that exhibit strong
acidity with pale yellow mottles of jarosite. The strong
acidity is a result of the oxidation of lacustrine and marine
sediments containing sulfides.
(3) Diagnostic Materials
Artefacts: Human-made materials that are not naturally
present on the Earth’s surface.
Calcaric sediments: Unconsolidated sediments containing
carbonates equivalent to or more than 40% CaCO 3 .
Fluvic materials: Fluvic, marine, and lacustrine unconsolidated sediments of Holocene age.
Hetero-soil materials: Soil materials classified as a soil
great group other than that of the bulk soil materials.
Organic materials: Materials mainly composed of
decomposed or undecomposed plant litter on the land surface. The materials should contain 20% or more of organic
carbon and should not show andic soil properties.
Peat materials: Materials mainly composed of decomposed or undecomposed plant litter accumulated under
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H. Shinjo and Y. Takata