central Kyushu passes from Mt. Hiko through the north of the
Chikushi Plain to Mt. Tara. The southern margin of central
Kyushu is the Usuki–Yatsushiro Tectonic Line, which is
considered as an extension of the Median Tectonic Line.
(1) Central Kyushu
Central Kyushu is characterized by numerous volcanoes,
normal faults, and seismic activity. This region is crossed by
a volcanic area and also contains an old volcanic mountainous area, a small non-volcanic area, and the Kumamoto
and Chikushi plains. The volcanic area contains volcanoes
such as Mt. Kuju, Mt. Aso, and Mt. Unzen, new and old
calderas formed post-Pliocene, a pyroclastic flow plateau,
and a lava plateau. The Chikushi Plain–Ariake Sea area is
the widest lowland in Kyushu and is considered to be a
sedimentary basin formed between the Beppu–Shimabara
graben and northern Kyushu.
(2) Northern Kyushu
Northern Kyushu consists of the Chikushi Mountains,
plains/basins, a western hilly low mountain area, and the
islands region. The plains/basins consist of the Fukuoka
Plain, the Ongagawa River lowland, and other areas. The
western hilly low mountain area consists of hills (Paleogene
and Miocene sedimentary rocks) and tableland composed of
basalt lava covering the Paleogene and Miocene rocks.
(3) Southern Kyushu
Southern Kyushu is subdivided into two parts: one is the
area having the geomorphological and geological features of
the “outer zone” of southwest Japan, and the other is the area
where the volcanoes are distributed. The former consists of
the Kyushu Mountains (accretionary complex), the Miyazaki
Plain, and the Osumi Peninsula (plutonic rocks). The latter
consists of the Kagoshima graben, ranging from the
Kobayashi basin to Mt. Kaimon, the Hisatsu/Kitasatu
mountainous area, and the Satsuma Peninsula. Numerous
calderas and pyroclastic flow plateaus originating from
volcanic activity are distributed in the Kagoshima graben.
(4) The Nansei Islands
The Nansei Islands are composed of the Satsunan Islands and
the Ryukyu Islands, which form the arcuate islands between
Kyushu and Taiwan (the Ryukyu Arc), and the Daito Islands,
which are located on the eastern side of the Ryukyu Arc and
consist of elevated coral reefs (Ota and Kawana 2001). The
Ryukyu Arc is divided into the following two chains by
topography and geology: (1) an island chain consisting of
volcanic islands from Iwo Jima to Iwo Tori Island through
the Tokara Islands (also known as the Tokara volcano island
chain); and (2) a non-volcanic island chain consisting of the
Satsunan Islands and the Ryukyu Islands excluding the
Tokara volcano island chain (Kato 2009). This non-volcanic
island chain consists of mountains and hills (accretionary
complex), hilly land (Neogene strata and Pleistocene calcareous sediment), and Holocene coral reefs.
10.1.2 Soil Distribution
The Kyushu–Okinawa region has an area of 45,000 km
2 ,
equal to 12% of Japan’s land area. Of the soil distributed
throughout the region, 34% are Andosols, 30% are Brown
Forest soils, 14% are Red-Yellow soils, 13% are Fluvic
soils, and 2% are Eutrosols (Table 2.4 in Chap. 2). The area
of cropland (paddy field, upland field, orchard, and tea field)
in the Kyushu–Okinawa region is about 568,000 ha, which
represents 15% of Japan’s arable land area (Statistics
Department, Minister’s Secretariat, Ministry of Agriculture,
Forestry and Fisheries 2016). Of the agricultural land in the
region, 44% is occupied by Fluvic soils, 28% by Andosols,
8% by Red-Yellow soils, and 5% by Eutrosols. Thus, the
croplands in the Kyushu–Okinawa region are characterized
by a high proportion of Fluvic soils, Red-Yellow soils, and
Andosols.
(1) Fluvic soils
This soil type is distributed in the lowlands of river basins
and is influenced by the geology around the plains and the
transportation and sedimentation by rivers. Among the soil
physicochemical properties reflected by these characteristics,
the mineral composition of the clay fraction and the particle
size fraction of the soil have great influences on the water
permeability, the nutrient supplying capacity, and other
factors. As volcanoes are distributed in Kyushu, the proportion of soil with an amorphous clay fraction is higher
there than in other regions (Soil Genesis and Classification
Laboratory, National Institute for Agro-Environmental Sciences, 1997). Based on their clay mineral composition, the
Fluvic soils in the Kyushu region are further classified into
the following four soil groups (Seino 1980). (1) Soils in the
reclaimed land around the Ariake Sea such as the Chikushi
Plain and the Kumamoto Plain. These soils have a fine
texture, are mainly composed of 2:1 clay minerals, and have
a high nutrient supplying capacity. Their productivity for
paddy rice is high, but drainage measures are required for
upland utilization. (2) Soils in the Nakatsu Plain and the
Miyazaki Plain. These soils have a medium texture and are
mainly composed of 1:1 clay minerals. (3) Soils in the
10 Kyushu and Okinawa Regions
331
Chikushi Plain to Mt. Tara. The southern margin of central
Kyushu is the Usuki–Yatsushiro Tectonic Line, which is
considered as an extension of the Median Tectonic Line.
(1) Central Kyushu
Central Kyushu is characterized by numerous volcanoes,
normal faults, and seismic activity. This region is crossed by
a volcanic area and also contains an old volcanic mountainous area, a small non-volcanic area, and the Kumamoto
and Chikushi plains. The volcanic area contains volcanoes
such as Mt. Kuju, Mt. Aso, and Mt. Unzen, new and old
calderas formed post-Pliocene, a pyroclastic flow plateau,
and a lava plateau. The Chikushi Plain–Ariake Sea area is
the widest lowland in Kyushu and is considered to be a
sedimentary basin formed between the Beppu–Shimabara
graben and northern Kyushu.
(2) Northern Kyushu
Northern Kyushu consists of the Chikushi Mountains,
plains/basins, a western hilly low mountain area, and the
islands region. The plains/basins consist of the Fukuoka
Plain, the Ongagawa River lowland, and other areas. The
western hilly low mountain area consists of hills (Paleogene
and Miocene sedimentary rocks) and tableland composed of
basalt lava covering the Paleogene and Miocene rocks.
(3) Southern Kyushu
Southern Kyushu is subdivided into two parts: one is the
area having the geomorphological and geological features of
the “outer zone” of southwest Japan, and the other is the area
where the volcanoes are distributed. The former consists of
the Kyushu Mountains (accretionary complex), the Miyazaki
Plain, and the Osumi Peninsula (plutonic rocks). The latter
consists of the Kagoshima graben, ranging from the
Kobayashi basin to Mt. Kaimon, the Hisatsu/Kitasatu
mountainous area, and the Satsuma Peninsula. Numerous
calderas and pyroclastic flow plateaus originating from
volcanic activity are distributed in the Kagoshima graben.
(4) The Nansei Islands
The Nansei Islands are composed of the Satsunan Islands and
the Ryukyu Islands, which form the arcuate islands between
Kyushu and Taiwan (the Ryukyu Arc), and the Daito Islands,
which are located on the eastern side of the Ryukyu Arc and
consist of elevated coral reefs (Ota and Kawana 2001). The
Ryukyu Arc is divided into the following two chains by
topography and geology: (1) an island chain consisting of
volcanic islands from Iwo Jima to Iwo Tori Island through
the Tokara Islands (also known as the Tokara volcano island
chain); and (2) a non-volcanic island chain consisting of the
Satsunan Islands and the Ryukyu Islands excluding the
Tokara volcano island chain (Kato 2009). This non-volcanic
island chain consists of mountains and hills (accretionary
complex), hilly land (Neogene strata and Pleistocene calcareous sediment), and Holocene coral reefs.
10.1.2 Soil Distribution
The Kyushu–Okinawa region has an area of 45,000 km
2 ,
equal to 12% of Japan’s land area. Of the soil distributed
throughout the region, 34% are Andosols, 30% are Brown
Forest soils, 14% are Red-Yellow soils, 13% are Fluvic
soils, and 2% are Eutrosols (Table 2.4 in Chap. 2). The area
of cropland (paddy field, upland field, orchard, and tea field)
in the Kyushu–Okinawa region is about 568,000 ha, which
represents 15% of Japan’s arable land area (Statistics
Department, Minister’s Secretariat, Ministry of Agriculture,
Forestry and Fisheries 2016). Of the agricultural land in the
region, 44% is occupied by Fluvic soils, 28% by Andosols,
8% by Red-Yellow soils, and 5% by Eutrosols. Thus, the
croplands in the Kyushu–Okinawa region are characterized
by a high proportion of Fluvic soils, Red-Yellow soils, and
Andosols.
(1) Fluvic soils
This soil type is distributed in the lowlands of river basins
and is influenced by the geology around the plains and the
transportation and sedimentation by rivers. Among the soil
physicochemical properties reflected by these characteristics,
the mineral composition of the clay fraction and the particle
size fraction of the soil have great influences on the water
permeability, the nutrient supplying capacity, and other
factors. As volcanoes are distributed in Kyushu, the proportion of soil with an amorphous clay fraction is higher
there than in other regions (Soil Genesis and Classification
Laboratory, National Institute for Agro-Environmental Sciences, 1997). Based on their clay mineral composition, the
Fluvic soils in the Kyushu region are further classified into
the following four soil groups (Seino 1980). (1) Soils in the
reclaimed land around the Ariake Sea such as the Chikushi
Plain and the Kumamoto Plain. These soils have a fine
texture, are mainly composed of 2:1 clay minerals, and have
a high nutrient supplying capacity. Their productivity for
paddy rice is high, but drainage measures are required for
upland utilization. (2) Soils in the Nakatsu Plain and the
Miyazaki Plain. These soils have a medium texture and are
mainly composed of 1:1 clay minerals. (3) Soils in the
10 Kyushu and Okinawa Regions
331