both soil groups are mainly used as paddy field. As mentioned below, Fluvic soils cover about 50% of Japanese
cultivated land, meaning that they are one of the most
important soil resources for Japanese food security.
(4) Red-Yellow Soils
Red-Yellow soils cover 7.6% of the total area of Japan and
are divided into two soil groups, namely Argic Red-Yellow
soils and Cambic Red-Yellow soils (refer to Cambisols).
Argic Red-Yellow soils are mainly distributed in the
southwestern part of Japan. Argic Red-Yellow soils correspond to several reference soil groups (Alisols, Acrisols,
Luvisols, and Lixisols) of the WRB2014 because our classification system definitions do not refer to the activity of
clay minerals and base saturation. Kanda et al. (2018)
reported that soils with low-activity clay are dominant in
western Kyushu (including Okinawa) and in Chubu,
whereas soils with high-activity clay are dominant in the
other regions. Thus, Argic Red-Yellow soils correspond to
Acrisols in western Kyushu and Chubu and to Alisols in all
the other regions (Kanda et al. 2018). In Japan, the distribution area of Cambic Red-Yellow soils is larger than that of
the argic soil group. However, this spatial distribution pattern is opposite in the western Kyushu and Chubu regions; in
these areas, argic horizons developed on stable landscape,
while cambic horizons developed on mountains or hill ranges. Takata et al. (2010) reported that in Japan, the
silt-to-clay ratio and cation exchange capacity (1 kg clay
base) of argic horizons are significantly lower than those of
cambic horizons in Red-Yellow soils. These results indicate
that the development of argic horizons requires long pedogenetic time and landscape stability and could be an indicator of soil weathering in Japan.
(5) Other Soil Groups
Regosols cover 6.9% of Japanese territory. This soil great
group is divided into four soil groups, namely Volcanogenous Regosols, Sandy Regosols, Lithosols, and Terrestrial Regosols. Volcanogenous Regosols are found at
active volcanic mountains/islands, Sandy Regosols are distributed in coastal dunes, and Lithosols are mainly distributed in high mountainous areas. Terrestrial Regosols
frequently occur in areas with landslides, especially those
where weathered granite is distributed; in general, granitic
Fig. 3.3 Distribution of volcanic tephra and Soil Groups in Kanto
district. Data source of active volcanic mountains: Japan Meteorological Agency website (https://www.data.jma.go.jp/svd/vois/data/tokyo/
STOCK/kaisetsu/katsukazan_toha/katsukazan_toha.html). Data source
of the depth volcanic ash: Uesugi et al. (1983). (Figure supplied by
Yusuke Takata)
3 Soil Classification and Distribution
65
cultivated land, meaning that they are one of the most
important soil resources for Japanese food security.
(4) Red-Yellow Soils
Red-Yellow soils cover 7.6% of the total area of Japan and
are divided into two soil groups, namely Argic Red-Yellow
soils and Cambic Red-Yellow soils (refer to Cambisols).
Argic Red-Yellow soils are mainly distributed in the
southwestern part of Japan. Argic Red-Yellow soils correspond to several reference soil groups (Alisols, Acrisols,
Luvisols, and Lixisols) of the WRB2014 because our classification system definitions do not refer to the activity of
clay minerals and base saturation. Kanda et al. (2018)
reported that soils with low-activity clay are dominant in
western Kyushu (including Okinawa) and in Chubu,
whereas soils with high-activity clay are dominant in the
other regions. Thus, Argic Red-Yellow soils correspond to
Acrisols in western Kyushu and Chubu and to Alisols in all
the other regions (Kanda et al. 2018). In Japan, the distribution area of Cambic Red-Yellow soils is larger than that of
the argic soil group. However, this spatial distribution pattern is opposite in the western Kyushu and Chubu regions; in
these areas, argic horizons developed on stable landscape,
while cambic horizons developed on mountains or hill ranges. Takata et al. (2010) reported that in Japan, the
silt-to-clay ratio and cation exchange capacity (1 kg clay
base) of argic horizons are significantly lower than those of
cambic horizons in Red-Yellow soils. These results indicate
that the development of argic horizons requires long pedogenetic time and landscape stability and could be an indicator of soil weathering in Japan.
(5) Other Soil Groups
Regosols cover 6.9% of Japanese territory. This soil great
group is divided into four soil groups, namely Volcanogenous Regosols, Sandy Regosols, Lithosols, and Terrestrial Regosols. Volcanogenous Regosols are found at
active volcanic mountains/islands, Sandy Regosols are distributed in coastal dunes, and Lithosols are mainly distributed in high mountainous areas. Terrestrial Regosols
frequently occur in areas with landslides, especially those
where weathered granite is distributed; in general, granitic
Fig. 3.3 Distribution of volcanic tephra and Soil Groups in Kanto
district. Data source of active volcanic mountains: Japan Meteorological Agency website (https://www.data.jma.go.jp/svd/vois/data/tokyo/
STOCK/kaisetsu/katsukazan_toha/katsukazan_toha.html). Data source
of the depth volcanic ash: Uesugi et al. (1983). (Figure supplied by
Yusuke Takata)
3 Soil Classification and Distribution
65