Sanuki (20) and Matsuyama (21) plains are located along the
coast of this region. The upper parts of these plains are
alluvial fans and the lower parts are deltaic plains (Hirai
2004).
The Kinki triangle zone is a lowland area that includes the
Oumi (22), Kyoto (23), and Nara (24) basins and the Osaka
plain (25) and is surrounded by small mountains. This
lowland area is covered by alluvial sediments or marine
sediments of the late Quaternary Period. The Oumi basin
lowland includes Lake Biwa (26), the largest freshwater lake
in Japan, and alluvial plains are widely located from the east
to the south of the lake. The Osaka plain and the Kyoto and
Nara basins were submerged under a series of seas and lakes
until the middle of the Quaternary Period and were divided
by crustal movement in the late Quaternary Period (Sangawa
2004). In the Kyoto basin, alluvial fans are developed in the
northeastern part, natural levees in the western part, and back
marshes in the southern part. All of the rivers flowing into
the Kyoto basin merge in the south of the basin and flow into
the Osaka Bay. Due to the narrow exit of the Kyoto basin, a
large swamp area was developed upstream of the exit. Here,
land reclamation by drainage has been carried out for the
development of agricultural land since the fourth century
(Tanioka 1964). The central part of the Osaka plain includes
an alluvial plain surrounded by hills and the Uemachi plateau. During the Jomon transgression (7–5 kya), the sea area
extended to the east of the Uemachi plateau. After the sea
level fell, lakes and marshes emerged in this area. Since the
fourth century, flood control, land reclamation by drainage,
river improvements, and changes to river courses have been
conducted to expand agricultural lands. The development of
agricultural land was also conducted along the coastal area
of the Osaka plain, expanding it to the west.
As a result of the long history of human activity in these
regions, artificially changed lands are widely distributed, not
only in the Kinki triangle zone but also in the mountains of
the inner zone and the Setouchi region.
9.1.3 Soil Distribution
1. Soils of the whole area
The soil distribution area and ratio by soil great group in the
Kinki, Chugoku, and Shikoku regions, according to the Soil
Classification System of Japan (The Fifth Committee for
Soil Classification and Nomenclature 2017), are shown in
Table 9.1 (calculated based on Obara et al. 2016). The major
soil great groups distributed in these regions are Brown
Forest soils, Red-Yellow soils, and Fluvic soils, which
together occupy about 80% of the land area of the regions
(Institute for Agro-Environmental Sciences, NARO 2017).
Brown Forest soils account for 47.6% of the soil area in
these three regions, much higher than the national average
(33.2%), and are distributed widely in mountainous areas.
Red-Yellow soils account for 16.0% of the whole area in the
regions, which is also much higher than the national average
(7.6%), and are distributed in lower-elevation mountainous
areas such as plateaus. A total of 44% of the Red-Yellow
soils in Japan is distributed in these regions, and this soil can
therefore be regarded as one of the distinctive characteristic
soils there. Fluvic soils account for 14.2% of the whole area
in these regions, which is close to the national average
(13.7%). There are not many large alluvial plains or basins
in the regions, but a number of small basins and lowlands
along rivers are located throughout mountains in the inner
zone. Fluvic soils are distributed in these small basins and
lowlands. Andosols, which account for 30.3% of the soil
area in Japan, account for only 8.6% of the whole area in the
Kinki, Chugoku, and Shikoku regions. This is because only
a small number of volcanoes were active in the Quaternary
Period in these regions. The small distribution of Andosols is
related to the wide distributions of Brown Forest soils and
Red-Yellow soils in these regions. Non-allophanic Andosols
comprise 84% of the Andosols in these three regions, which
is much higher than the national average (23.9%) (Obara
et al. 2016). This is related to the fact that Andosols in this
region have poor depositions of Holocene tephra. Regosols
account for 7.9% of the whole area in these regions, which is
similar to the national average (6.9%). Among Regosols,
Terrestrial Regosols are dominant, with 36.6% of the Terrestrial Regosols in Japan being distributed in these regions
(Obara et al. 2016). This is related to the wide distribution of
“Masa” soil, which is derived from the residue of weathered
granite.
2. Soils of agricultural land
The soil distribution area and ratio by soil great group in
agricultural lands in the Kinki, Chugoku, and Shikoku
regions, according to the Soil Classification System of Japan
(The Fifth Committee for Soil Classification and Nomenclature 2017), are shown in Table 9.2 (calculated based on
Kanda et al. 2017). Fluvic soils are distributed most widely
and occupy 65.5% of agricultural land in these regions,
much higher than the national average (47.4%). Fluvic
Paddy soils, Gley Fluvic soils, and Gray Fluvic soils account
for 44.1%, 23.1%, and 21.3% of Fluvic soils in these
regions, respectively (Kanda et al. 2017). These three soil
groups are usually used as paddy fields, which is reflected in
the high ratio of paddy fields in the total agricultural land
area in the three regions (72.8%). In these regions, large
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J. Yanai et al.
coast of this region. The upper parts of these plains are
alluvial fans and the lower parts are deltaic plains (Hirai
2004).
The Kinki triangle zone is a lowland area that includes the
Oumi (22), Kyoto (23), and Nara (24) basins and the Osaka
plain (25) and is surrounded by small mountains. This
lowland area is covered by alluvial sediments or marine
sediments of the late Quaternary Period. The Oumi basin
lowland includes Lake Biwa (26), the largest freshwater lake
in Japan, and alluvial plains are widely located from the east
to the south of the lake. The Osaka plain and the Kyoto and
Nara basins were submerged under a series of seas and lakes
until the middle of the Quaternary Period and were divided
by crustal movement in the late Quaternary Period (Sangawa
2004). In the Kyoto basin, alluvial fans are developed in the
northeastern part, natural levees in the western part, and back
marshes in the southern part. All of the rivers flowing into
the Kyoto basin merge in the south of the basin and flow into
the Osaka Bay. Due to the narrow exit of the Kyoto basin, a
large swamp area was developed upstream of the exit. Here,
land reclamation by drainage has been carried out for the
development of agricultural land since the fourth century
(Tanioka 1964). The central part of the Osaka plain includes
an alluvial plain surrounded by hills and the Uemachi plateau. During the Jomon transgression (7–5 kya), the sea area
extended to the east of the Uemachi plateau. After the sea
level fell, lakes and marshes emerged in this area. Since the
fourth century, flood control, land reclamation by drainage,
river improvements, and changes to river courses have been
conducted to expand agricultural lands. The development of
agricultural land was also conducted along the coastal area
of the Osaka plain, expanding it to the west.
As a result of the long history of human activity in these
regions, artificially changed lands are widely distributed, not
only in the Kinki triangle zone but also in the mountains of
the inner zone and the Setouchi region.
9.1.3 Soil Distribution
1. Soils of the whole area
The soil distribution area and ratio by soil great group in the
Kinki, Chugoku, and Shikoku regions, according to the Soil
Classification System of Japan (The Fifth Committee for
Soil Classification and Nomenclature 2017), are shown in
Table 9.1 (calculated based on Obara et al. 2016). The major
soil great groups distributed in these regions are Brown
Forest soils, Red-Yellow soils, and Fluvic soils, which
together occupy about 80% of the land area of the regions
(Institute for Agro-Environmental Sciences, NARO 2017).
Brown Forest soils account for 47.6% of the soil area in
these three regions, much higher than the national average
(33.2%), and are distributed widely in mountainous areas.
Red-Yellow soils account for 16.0% of the whole area in the
regions, which is also much higher than the national average
(7.6%), and are distributed in lower-elevation mountainous
areas such as plateaus. A total of 44% of the Red-Yellow
soils in Japan is distributed in these regions, and this soil can
therefore be regarded as one of the distinctive characteristic
soils there. Fluvic soils account for 14.2% of the whole area
in these regions, which is close to the national average
(13.7%). There are not many large alluvial plains or basins
in the regions, but a number of small basins and lowlands
along rivers are located throughout mountains in the inner
zone. Fluvic soils are distributed in these small basins and
lowlands. Andosols, which account for 30.3% of the soil
area in Japan, account for only 8.6% of the whole area in the
Kinki, Chugoku, and Shikoku regions. This is because only
a small number of volcanoes were active in the Quaternary
Period in these regions. The small distribution of Andosols is
related to the wide distributions of Brown Forest soils and
Red-Yellow soils in these regions. Non-allophanic Andosols
comprise 84% of the Andosols in these three regions, which
is much higher than the national average (23.9%) (Obara
et al. 2016). This is related to the fact that Andosols in this
region have poor depositions of Holocene tephra. Regosols
account for 7.9% of the whole area in these regions, which is
similar to the national average (6.9%). Among Regosols,
Terrestrial Regosols are dominant, with 36.6% of the Terrestrial Regosols in Japan being distributed in these regions
(Obara et al. 2016). This is related to the wide distribution of
“Masa” soil, which is derived from the residue of weathered
granite.
2. Soils of agricultural land
The soil distribution area and ratio by soil great group in
agricultural lands in the Kinki, Chugoku, and Shikoku
regions, according to the Soil Classification System of Japan
(The Fifth Committee for Soil Classification and Nomenclature 2017), are shown in Table 9.2 (calculated based on
Kanda et al. 2017). Fluvic soils are distributed most widely
and occupy 65.5% of agricultural land in these regions,
much higher than the national average (47.4%). Fluvic
Paddy soils, Gley Fluvic soils, and Gray Fluvic soils account
for 44.1%, 23.1%, and 21.3% of Fluvic soils in these
regions, respectively (Kanda et al. 2017). These three soil
groups are usually used as paddy fields, which is reflected in
the high ratio of paddy fields in the total agricultural land
area in the three regions (72.8%). In these regions, large
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J. Yanai et al.