(1) Contains more than 12% organic carbon; and
(2) Does not have andic soil properties, except when plant
fibers comprise more than one sixth of the volume after
rubbing in the hands.
Therefore, all of the soils under Organic soils are classified in the Peat soil group. Most of these soils are classified
as Histosols in the USDA Soil Taxonomy. However, it
requires the thickness of “organic soil material” to be more
than 40 cm, and therefore, some of the Peat soils may not be
classified as Histosols under Soil Taxonomy (Soil Survey
Staff 2014). This is because Japanese Peat soils are strongly
affected by inputs of inorganic material from the flooding of
rivers and volcanic ash deposition, as will be discussed later
(refer to Sect. 4.2.2).
Peat soils have received dressings of mineral soils for
improving the chemical and physical characteristics of rice
paddies and grasslands in Hokkaido, where large areas are
occupied by Organic soils (refer to Sect. 4.2.4). When the
thickness of dressed soil is less than 35 cm and organic soil
material extends below the layer, a soil is classified as
Organic soil because of the large influence of organic soil
material. A soil is classified as Human-made soil when the
thickness of the dressed soil layer is more than 35 cm.
In Japan, Peat soils had been classified as High-moor Peat
soils, Transitional-moor Peat soils, and Low-moor Peat soils
according to the formation process and the types of plant
species included in their composition. This system was
based on the peat soil classification of Germany, and the
subsequent translations. Peat soils are additionally classified
by their nutrient status into Eutrophic Peat soils and Oligotrophic Peat soils, as well as Mesotrophic Peat soils, which
are intermediate between the previous two. Low-moor Peat
soils correspond to Eutrophic Peat soils and High-moor Peat
soils correspond to Oligotrophic Peat soils.
The Soil Classification System of Japan is based on the
degree of decomposition of Peat soils and the type of
component plant species and is divided into the following
four soil subgroups:
• Sapric Peat soils: Peat soils that have soil layers of organic soil material with the highest fraction of sapric soil
material being between the soil surface and a depth of
50 cm; or
• High-moor Peat soils: other Peat soils in which the
uppermost 25 cm of soil layers is composed of
High-moor organic soil material; or
• Transitional-moor Peat soils: other Peat soils in which the
uppermost 25 cm of soil layers is composed of organic
soil material with transitional-moor soil materials; or.
• Low-moor Peat soils: other Peat soils.
The organic soil materials mentioned above are defined
based on the degree of decomposition of Peat soils as well as
the type of component plant species.
• Fibric soil materials: those that contain three quarters or
more by volume of fibers after rubbing.
• Sapric soil materials: those that contain less than
one-sixth by volume of fibers after rubbing.
• Hemic soil materials: other organic soil materials that are
not classified as fibric soil materials or sapric soil
materials.
• High-moor soil materials: those that have the highest
fraction (area) of the combination of Sphagnum, Horomui
sedge (Carex middendorffii), small cranberry (Vaccinium
oxycoccos), whitebeak sedge (Rhynchospora alba), and
Rannoch-rush (Scheuchzeria palustris).
• Transitional-moor soil materials: those that have the
highest fraction (area) of Japanese moor grass (Moliniopsis japonica), hare’s-tail cottongrass (Eriophorum
vaginatum), Myrica gale (Myrica gale var. tomentosa),
and Sakhalin spruce (Picea glehnii) combined in organic
soil materials.
• Low-moor soil materials: other organic soil materials that
are not classified as high-moor organic soil materials or
transitional-moor organic soil materials.
Under the classical Japanese soil classification system, the
Classification of Cultivated Soils in Japan (Cultivated Soil
Classification Committee 1995), Sapric Peat soils were classified as Muck soils, which have highly decomposed organic
soil materials and a high degree of humification, which makes
it difficult to identify plant fibers, and the soil colors appear
black to dark brown. These soils are classified as Saprists in
the USDA Soil Taxonomy based on plant fiber content and
sodium pyrophosphate index (PI; Soil Survey Staff 2014). In
Japan, the input of inorganic soil materials from the flooding
of rivers and from volcanic ash deposition is often observed,
accelerating the decomposition of Peat soils above and below
the incorporated inorganic soil materials.
High-moor, Transitional-moor, and Low-moor Peat soils
are composed of fibric or hemic soil materials and classified
into three soil subgroups according to the type of component
plant species. In the USDA Soil Taxonomy, peat soils that are
composed of fibric soil materials are classified as Fibrists and
other peat soils that are composed of hemic soil materials are
classified as Hemists (Soil Survey Staff 2014). In Japan, much
of the peatlands are formed in the back swamp of an alluvial
plain. Low-moor Peat soils dominate and are mainly composed of common reed (Phragmites australis) and Japanese
alder (Alnus japonica). The areas occupied by High-moor or
Transitional-moor Peat soils are relatively small.
4 Major Soil Types
75
(2) Does not have andic soil properties, except when plant
fibers comprise more than one sixth of the volume after
rubbing in the hands.
Therefore, all of the soils under Organic soils are classified in the Peat soil group. Most of these soils are classified
as Histosols in the USDA Soil Taxonomy. However, it
requires the thickness of “organic soil material” to be more
than 40 cm, and therefore, some of the Peat soils may not be
classified as Histosols under Soil Taxonomy (Soil Survey
Staff 2014). This is because Japanese Peat soils are strongly
affected by inputs of inorganic material from the flooding of
rivers and volcanic ash deposition, as will be discussed later
(refer to Sect. 4.2.2).
Peat soils have received dressings of mineral soils for
improving the chemical and physical characteristics of rice
paddies and grasslands in Hokkaido, where large areas are
occupied by Organic soils (refer to Sect. 4.2.4). When the
thickness of dressed soil is less than 35 cm and organic soil
material extends below the layer, a soil is classified as
Organic soil because of the large influence of organic soil
material. A soil is classified as Human-made soil when the
thickness of the dressed soil layer is more than 35 cm.
In Japan, Peat soils had been classified as High-moor Peat
soils, Transitional-moor Peat soils, and Low-moor Peat soils
according to the formation process and the types of plant
species included in their composition. This system was
based on the peat soil classification of Germany, and the
subsequent translations. Peat soils are additionally classified
by their nutrient status into Eutrophic Peat soils and Oligotrophic Peat soils, as well as Mesotrophic Peat soils, which
are intermediate between the previous two. Low-moor Peat
soils correspond to Eutrophic Peat soils and High-moor Peat
soils correspond to Oligotrophic Peat soils.
The Soil Classification System of Japan is based on the
degree of decomposition of Peat soils and the type of
component plant species and is divided into the following
four soil subgroups:
• Sapric Peat soils: Peat soils that have soil layers of organic soil material with the highest fraction of sapric soil
material being between the soil surface and a depth of
50 cm; or
• High-moor Peat soils: other Peat soils in which the
uppermost 25 cm of soil layers is composed of
High-moor organic soil material; or
• Transitional-moor Peat soils: other Peat soils in which the
uppermost 25 cm of soil layers is composed of organic
soil material with transitional-moor soil materials; or.
• Low-moor Peat soils: other Peat soils.
The organic soil materials mentioned above are defined
based on the degree of decomposition of Peat soils as well as
the type of component plant species.
• Fibric soil materials: those that contain three quarters or
more by volume of fibers after rubbing.
• Sapric soil materials: those that contain less than
one-sixth by volume of fibers after rubbing.
• Hemic soil materials: other organic soil materials that are
not classified as fibric soil materials or sapric soil
materials.
• High-moor soil materials: those that have the highest
fraction (area) of the combination of Sphagnum, Horomui
sedge (Carex middendorffii), small cranberry (Vaccinium
oxycoccos), whitebeak sedge (Rhynchospora alba), and
Rannoch-rush (Scheuchzeria palustris).
• Transitional-moor soil materials: those that have the
highest fraction (area) of Japanese moor grass (Moliniopsis japonica), hare’s-tail cottongrass (Eriophorum
vaginatum), Myrica gale (Myrica gale var. tomentosa),
and Sakhalin spruce (Picea glehnii) combined in organic
soil materials.
• Low-moor soil materials: other organic soil materials that
are not classified as high-moor organic soil materials or
transitional-moor organic soil materials.
Under the classical Japanese soil classification system, the
Classification of Cultivated Soils in Japan (Cultivated Soil
Classification Committee 1995), Sapric Peat soils were classified as Muck soils, which have highly decomposed organic
soil materials and a high degree of humification, which makes
it difficult to identify plant fibers, and the soil colors appear
black to dark brown. These soils are classified as Saprists in
the USDA Soil Taxonomy based on plant fiber content and
sodium pyrophosphate index (PI; Soil Survey Staff 2014). In
Japan, the input of inorganic soil materials from the flooding
of rivers and from volcanic ash deposition is often observed,
accelerating the decomposition of Peat soils above and below
the incorporated inorganic soil materials.
High-moor, Transitional-moor, and Low-moor Peat soils
are composed of fibric or hemic soil materials and classified
into three soil subgroups according to the type of component
plant species. In the USDA Soil Taxonomy, peat soils that are
composed of fibric soil materials are classified as Fibrists and
other peat soils that are composed of hemic soil materials are
classified as Hemists (Soil Survey Staff 2014). In Japan, much
of the peatlands are formed in the back swamp of an alluvial
plain. Low-moor Peat soils dominate and are mainly composed of common reed (Phragmites australis) and Japanese
alder (Alnus japonica). The areas occupied by High-moor or
Transitional-moor Peat soils are relatively small.
4 Major Soil Types
75