natural climax vegetation under these climatic conditions is
basically forest, except in high mountains and wet lowlands,
where the vegetation is grassland or sphagnum.
1.1.2 Landscapes and Geology
The Japanese islands are covered with volcanic ejecta along
its volcanic belt, which is part of the orogenic belt, and have
a lot of earthquakes and volcanic activity. The Japanese
islands are part of the circum-Pacific volcanic belt and
contain two distinct volcanic belts. One is the East Japan
volcanic belt, which runs from east to west through Hokkaido, the west side of Tohoku, the northern part of
Koushinetsu to the Izu Islands and Iou Islands, and to the
Mariana Trench. The other is the West Japan volcanic belt,
which runs from the Sea of Japan side of the Chugoku
region (San’in area), through Kyushu and to the Nansei
Islands. Volcanic rocks are generally composed of silica-rich
andesite and rhyolite, although alkaline basalts are seen in
Kyushu. Terrain changes, such as mountain erosion and
plain formation due to sedimentation in flat areas, are fast
and intense under the humid monsoon climate.
1.1.3 Soils
The soils of Japan are immature soils of about 10,000 years
in age. Their parent materials are volcanic tephra or ejecta or
eroded or deposited materials. In 2017, Japanese Society of
Pedology developed a new soil classification system, the
“Soil Classification System of Japan,” to consider these
factors (Fifth Committee for Soil Classification and
Nomenclature 2017). According to that classification system, Brown Forest soils cover 33.2% of the country, and
Andosols, Fluvic soils, Red-Yellow soils, and Regosols
cover 30.3%, 13.7%, 7.6%, and 6.9%, respectively. Peat
soils are also distributed around the rivers and coasts of
Hokkaido and cover 3% of that island’s area. Brown Forest
soils do not have andic properties, and although those rock
structures are lost, clay formation and soil structure development are observed. Brown Forest soils mainly correspond
to Cambisols in the World Reference Base for Soil
Resources (WRB). Andosols are derived from volcanic ash,
have andic properties, and correspond to Andosols in the
WRB. Fluvisols correspond to Fluvisols in the WRB; their
parent materials are sediment deposits in rivers, seas, and
lakes. Paddy field soils are also classified as Fluvisols in the
Japanese taxonomic system, but those soils are classified as
Anthrosols in the WRB. Red-Yellow soils are well weathered and relatively developed soils in Japan. Some
Red-Yellow soils have argic horizons and also include soils
that have cambic horizons. The criterion of cation exchange
capacity per 1 kg of clay is not defined in our system, and
so, there is no soil group corresponding to Acrisols, Lixisols,
Alisols, or Luvisols in the WRB. Regosols correspond to
Regosols and Lithosols in the WRB, and Peat soils to Histosols. Japanese soils are generally acidic, since the basic
cations of soils are leached by the high precipitation of the
monsoon climate.
The crystalline clay mineral composition of Fluvisols
tends to be 2:1 in Northern Japan and 1:1 in Southern Japan.
Minerals with a size of 1.4 nm are dominant in the Hokkaido, Tohoku, and Hokuriku regions, and minerals with a
size of 0.7 nm are dominant in the Chugoku, Shikoku, and
Kyushu regions, and the composition of those minerals are
balanced in the Kanto, Tokai, and Kinki regions (Soil
Genesis and Classification Laboratory 1996). Andosols have
a high phosphate fixation capacity and are divided into
allophanic Andosols and non-allophanic Andosols, the latter
of which have low pH. allophanic Andosols are distributed
in the Hokkaido, Tohoku, Kanto, and Kyushu regions,
where Holocene volcanic ejecta are deposited, whereas
non-allophanic Andosols are distributed in the Tokai,
Hokuriku, Kinki, Chugoku, and Shikoku regions, where
Holocene volcanic ejecta is absent.
1.2 Material Cycling and Environmental
Problems in Agriculture
(1) Material cycling through soil
In ecosystems, energy, water, and materials constantly enter
and leave, and produce soil (shown schematically in
Fig. 1.2). In plants, solar energy is consumed by photosynthesis and transpiration, atmospheric carbon dioxide (CO 2 ) is
absorbed via the leaves, water and nutrients are absorbed via
the roots and plant growth occurs. The nutrients absorbed by
plants include ammonia (NH 3 ) synthesized from nitrogen
gas (N 2 ) in the atmosphere by nitrogen-fixing bacteria and
minerals supplied by the hydrolysis of rock minerals (CO 2
dissolved in rainwater acts as a weathering agent by supplying protons from carbonic acid). When a plant dies and is
decomposed by microorganisms in the soil, CO 2 is discharged, and weathering is accelerated in the soil. At the
same time, NH 3 and minerals are released into the soil. The
NH 3 dissolves in the soil solution to form ammonium ions
(NH 4
+
), and a part of it is converted into nitrate ions (NO 3
– )
by nitrifying bacteria and is reabsorbed by plants. Inorganic
nitrogen, minerals that are not absorbed by plants, and
bicarbonate ions produced by the dissolution of CO 2 are
subsequently leached out due to the penetration of water in
the soil, before moving into groundwater and flowing out to
rivers.
1 Overview
5
basically forest, except in high mountains and wet lowlands,
where the vegetation is grassland or sphagnum.
1.1.2 Landscapes and Geology
The Japanese islands are covered with volcanic ejecta along
its volcanic belt, which is part of the orogenic belt, and have
a lot of earthquakes and volcanic activity. The Japanese
islands are part of the circum-Pacific volcanic belt and
contain two distinct volcanic belts. One is the East Japan
volcanic belt, which runs from east to west through Hokkaido, the west side of Tohoku, the northern part of
Koushinetsu to the Izu Islands and Iou Islands, and to the
Mariana Trench. The other is the West Japan volcanic belt,
which runs from the Sea of Japan side of the Chugoku
region (San’in area), through Kyushu and to the Nansei
Islands. Volcanic rocks are generally composed of silica-rich
andesite and rhyolite, although alkaline basalts are seen in
Kyushu. Terrain changes, such as mountain erosion and
plain formation due to sedimentation in flat areas, are fast
and intense under the humid monsoon climate.
1.1.3 Soils
The soils of Japan are immature soils of about 10,000 years
in age. Their parent materials are volcanic tephra or ejecta or
eroded or deposited materials. In 2017, Japanese Society of
Pedology developed a new soil classification system, the
“Soil Classification System of Japan,” to consider these
factors (Fifth Committee for Soil Classification and
Nomenclature 2017). According to that classification system, Brown Forest soils cover 33.2% of the country, and
Andosols, Fluvic soils, Red-Yellow soils, and Regosols
cover 30.3%, 13.7%, 7.6%, and 6.9%, respectively. Peat
soils are also distributed around the rivers and coasts of
Hokkaido and cover 3% of that island’s area. Brown Forest
soils do not have andic properties, and although those rock
structures are lost, clay formation and soil structure development are observed. Brown Forest soils mainly correspond
to Cambisols in the World Reference Base for Soil
Resources (WRB). Andosols are derived from volcanic ash,
have andic properties, and correspond to Andosols in the
WRB. Fluvisols correspond to Fluvisols in the WRB; their
parent materials are sediment deposits in rivers, seas, and
lakes. Paddy field soils are also classified as Fluvisols in the
Japanese taxonomic system, but those soils are classified as
Anthrosols in the WRB. Red-Yellow soils are well weathered and relatively developed soils in Japan. Some
Red-Yellow soils have argic horizons and also include soils
that have cambic horizons. The criterion of cation exchange
capacity per 1 kg of clay is not defined in our system, and
so, there is no soil group corresponding to Acrisols, Lixisols,
Alisols, or Luvisols in the WRB. Regosols correspond to
Regosols and Lithosols in the WRB, and Peat soils to Histosols. Japanese soils are generally acidic, since the basic
cations of soils are leached by the high precipitation of the
monsoon climate.
The crystalline clay mineral composition of Fluvisols
tends to be 2:1 in Northern Japan and 1:1 in Southern Japan.
Minerals with a size of 1.4 nm are dominant in the Hokkaido, Tohoku, and Hokuriku regions, and minerals with a
size of 0.7 nm are dominant in the Chugoku, Shikoku, and
Kyushu regions, and the composition of those minerals are
balanced in the Kanto, Tokai, and Kinki regions (Soil
Genesis and Classification Laboratory 1996). Andosols have
a high phosphate fixation capacity and are divided into
allophanic Andosols and non-allophanic Andosols, the latter
of which have low pH. allophanic Andosols are distributed
in the Hokkaido, Tohoku, Kanto, and Kyushu regions,
where Holocene volcanic ejecta are deposited, whereas
non-allophanic Andosols are distributed in the Tokai,
Hokuriku, Kinki, Chugoku, and Shikoku regions, where
Holocene volcanic ejecta is absent.
1.2 Material Cycling and Environmental
Problems in Agriculture
(1) Material cycling through soil
In ecosystems, energy, water, and materials constantly enter
and leave, and produce soil (shown schematically in
Fig. 1.2). In plants, solar energy is consumed by photosynthesis and transpiration, atmospheric carbon dioxide (CO 2 ) is
absorbed via the leaves, water and nutrients are absorbed via
the roots and plant growth occurs. The nutrients absorbed by
plants include ammonia (NH 3 ) synthesized from nitrogen
gas (N 2 ) in the atmosphere by nitrogen-fixing bacteria and
minerals supplied by the hydrolysis of rock minerals (CO 2
dissolved in rainwater acts as a weathering agent by supplying protons from carbonic acid). When a plant dies and is
decomposed by microorganisms in the soil, CO 2 is discharged, and weathering is accelerated in the soil. At the
same time, NH 3 and minerals are released into the soil. The
NH 3 dissolves in the soil solution to form ammonium ions
(NH 4
+
), and a part of it is converted into nitrate ions (NO 3
– )
by nitrifying bacteria and is reabsorbed by plants. Inorganic
nitrogen, minerals that are not absorbed by plants, and
bicarbonate ions produced by the dissolution of CO 2 are
subsequently leached out due to the penetration of water in
the soil, before moving into groundwater and flowing out to
rivers.
1 Overview
5