4.4.8 Management and Use of Podzols
In Japan, most Podzols are limited to forestry areas. In
Podzols in the Kiso area (Fig. 4.21), forestry can produce
excellent cypress timber. Due to steep slopes, alpine climate,
and low productivity, Podzols are vulnerable to intensive
use. The removal of the O horizon and erosion can cause a
sharp decline in forest productivity or the failure of natural
regeneration. Podzols are preserved or managed in national
parks and non-private forests. This contrasts with the
intensive potato production that occurs in Podzols in Canada
(esp., Prince Edward Island). In Japan, Podzols provide
habitats for rare alpine plants and ptarmigan nesting under
Pinus pumila. Considering the uniqueness of Podzols, erosion management or preservation is required.
4.5 Fluvic Soils
4.5.1 Introduction
Fluvic soils are young soils developed from recent alluvial
deposits. They occur on alluvial plains, river fans, valleys,
and tidal marshes and occupy a significant proportion of the
land surface (about 5200 km
2 ), amounting to approximately
14% of Japan’s total land surface and 47% of its total crop
field land (Fig. 4.30). Fluvic soils are usually fertile with
weakly acidic to neutral soil reaction. These soils are used
widely as paddy fields, and some well-drained soils are used
for upland crops, vegetables, orchards, and grassland.
Fluvic soils are strongly affected by the variety of landform, relief, and moisture status of flood plains (Fig. 4.31).
Natural levees consisting of sandy sediments occur adjacent
to present or former river beds. Levees form the highest parts
of the surrounding landscape and are freely drained. Brown
Fluvic soils and Fluvic Paddy soils are widely found on
levees. Old levees are used for upland crop fields and residential areas. Additionally, in suburban areas, many kinds of
vegetables are grown on old levees.
Back swamp occurs behind the lower-lying levee area
and consists of heavier-textured particles. In back swamps,
the accumulation of organic matter is common, and Gley
Fluvic soils, Gray Fluvic soils, and Peat soils are distributed.
In Japan, back swamps are widely used for paddy fields,
except in cold regions in northern and eastern parts of
Hokkaido.
Fans (alluvial fans) are fan- or cone-shaped deposits of
sediment built up by streams and are widely distributed in
Japan. Fans are generally well-drained, have a
coarse-grained texture with gravel and boulders and have
gentle to medium slopes. On fans, mainly Brown Fluvic
soils and Regosolic Fluvic soils are distributed. Fans are
used for orchards, upland crops, and paddy fields with
irrigation water. Some fans in steep mountainous areas are
used for forest or left as wasteland.
Reclaimed land: Japan has a long history of marsh
reclamation: since the 1600s (the Edo era), wide areas of
paddy fields have been reclaimed from the sea. Gley Fluvic
soils are the major soils appearing on reclaimed lands. Lands
were reclaimed for paddy rice cultivation before the 1970s;
however, in the 1970s, when national self-sufficiency of rice
was attained, it was attempted to convert reclaimed lands
into multipurpose crop fields.
4.5.2 Soil Classification of Fluvic Soils
Paddy fields are widely distributed in alluvial plains in
Japan. Since rice is the most important cereal crop in Japan,
many studies have been conducted on paddy soil, and a
unique soil classification for paddy soil has emerged.
Paddy soils, both artificially and naturally, are submerged
at least 3–4 months a year. During most of this period, the
surface layer is kept in a reduced state, and the paddy soils
have unique characteristics compared with the upland soils.
However, these unique characteristics had not been recognized in the early soil classification system. For alluvial soils
in Japan, Kamoshita (1940) adopted a scientific soil classification. He introduced the groundwater soil type
(hydro-sequence system) developed in Germany for the
preparation of soil survey reports. Groundwater soil types in
this classification, i.e., Bog soil, Half-bog soil, Meadow soil,
Gray Lowland soil, and Brown Lowland soil, were the basis
of Japanese soil classification for alluvial soils under natural
aquic conditions, but his soil classification system did not
introduce any unique characteristics derived from the irrigation period specific to paddy fields. Uchiyama (1949)
published the first soil classification referring to the characteristics of the subsurface layer of paddy soil derived from
the submerged condition for a certain period. In his classification, aquic conditions resulting from continuous irrigation in well-drained paddy fields were found to promote the
development of unique soil profiles, i.e., iron and manganese
accumulation layers, in the subsurface layer. Following the
classification of Uchiyama, several soil classifications were
proposed for paddy field soils (Kanno 1957; Yamazaki
1960; Matsui et al. 1961). The characteristics developed
under the influence of artificial irrigation of paddy fields
were studied in detail, and a comprehensive classification
framework including soil development under groundwater
(natural) and artificial aquic conditions was proposed by
Mitsuchi (1974). Although this framework was adapted to
the soil classification system after Japan, some diagnostic
horizons and properties were adopted in the USDA Soil
Classification (1990) and World Reference Base for soil
resources (IUSS Working Group 1998).
4 Major Soil Types
99
In Japan, most Podzols are limited to forestry areas. In
Podzols in the Kiso area (Fig. 4.21), forestry can produce
excellent cypress timber. Due to steep slopes, alpine climate,
and low productivity, Podzols are vulnerable to intensive
use. The removal of the O horizon and erosion can cause a
sharp decline in forest productivity or the failure of natural
regeneration. Podzols are preserved or managed in national
parks and non-private forests. This contrasts with the
intensive potato production that occurs in Podzols in Canada
(esp., Prince Edward Island). In Japan, Podzols provide
habitats for rare alpine plants and ptarmigan nesting under
Pinus pumila. Considering the uniqueness of Podzols, erosion management or preservation is required.
4.5 Fluvic Soils
4.5.1 Introduction
Fluvic soils are young soils developed from recent alluvial
deposits. They occur on alluvial plains, river fans, valleys,
and tidal marshes and occupy a significant proportion of the
land surface (about 5200 km
2 ), amounting to approximately
14% of Japan’s total land surface and 47% of its total crop
field land (Fig. 4.30). Fluvic soils are usually fertile with
weakly acidic to neutral soil reaction. These soils are used
widely as paddy fields, and some well-drained soils are used
for upland crops, vegetables, orchards, and grassland.
Fluvic soils are strongly affected by the variety of landform, relief, and moisture status of flood plains (Fig. 4.31).
Natural levees consisting of sandy sediments occur adjacent
to present or former river beds. Levees form the highest parts
of the surrounding landscape and are freely drained. Brown
Fluvic soils and Fluvic Paddy soils are widely found on
levees. Old levees are used for upland crop fields and residential areas. Additionally, in suburban areas, many kinds of
vegetables are grown on old levees.
Back swamp occurs behind the lower-lying levee area
and consists of heavier-textured particles. In back swamps,
the accumulation of organic matter is common, and Gley
Fluvic soils, Gray Fluvic soils, and Peat soils are distributed.
In Japan, back swamps are widely used for paddy fields,
except in cold regions in northern and eastern parts of
Hokkaido.
Fans (alluvial fans) are fan- or cone-shaped deposits of
sediment built up by streams and are widely distributed in
Japan. Fans are generally well-drained, have a
coarse-grained texture with gravel and boulders and have
gentle to medium slopes. On fans, mainly Brown Fluvic
soils and Regosolic Fluvic soils are distributed. Fans are
used for orchards, upland crops, and paddy fields with
irrigation water. Some fans in steep mountainous areas are
used for forest or left as wasteland.
Reclaimed land: Japan has a long history of marsh
reclamation: since the 1600s (the Edo era), wide areas of
paddy fields have been reclaimed from the sea. Gley Fluvic
soils are the major soils appearing on reclaimed lands. Lands
were reclaimed for paddy rice cultivation before the 1970s;
however, in the 1970s, when national self-sufficiency of rice
was attained, it was attempted to convert reclaimed lands
into multipurpose crop fields.
4.5.2 Soil Classification of Fluvic Soils
Paddy fields are widely distributed in alluvial plains in
Japan. Since rice is the most important cereal crop in Japan,
many studies have been conducted on paddy soil, and a
unique soil classification for paddy soil has emerged.
Paddy soils, both artificially and naturally, are submerged
at least 3–4 months a year. During most of this period, the
surface layer is kept in a reduced state, and the paddy soils
have unique characteristics compared with the upland soils.
However, these unique characteristics had not been recognized in the early soil classification system. For alluvial soils
in Japan, Kamoshita (1940) adopted a scientific soil classification. He introduced the groundwater soil type
(hydro-sequence system) developed in Germany for the
preparation of soil survey reports. Groundwater soil types in
this classification, i.e., Bog soil, Half-bog soil, Meadow soil,
Gray Lowland soil, and Brown Lowland soil, were the basis
of Japanese soil classification for alluvial soils under natural
aquic conditions, but his soil classification system did not
introduce any unique characteristics derived from the irrigation period specific to paddy fields. Uchiyama (1949)
published the first soil classification referring to the characteristics of the subsurface layer of paddy soil derived from
the submerged condition for a certain period. In his classification, aquic conditions resulting from continuous irrigation in well-drained paddy fields were found to promote the
development of unique soil profiles, i.e., iron and manganese
accumulation layers, in the subsurface layer. Following the
classification of Uchiyama, several soil classifications were
proposed for paddy field soils (Kanno 1957; Yamazaki
1960; Matsui et al. 1961). The characteristics developed
under the influence of artificial irrigation of paddy fields
were studied in detail, and a comprehensive classification
framework including soil development under groundwater
(natural) and artificial aquic conditions was proposed by
Mitsuchi (1974). Although this framework was adapted to
the soil classification system after Japan, some diagnostic
horizons and properties were adopted in the USDA Soil
Classification (1990) and World Reference Base for soil
resources (IUSS Working Group 1998).
4 Major Soil Types
99