year is not well weathered and is classified as Volcanogenous Regosol. In the southern half of Hokkaido,
volcanic ash soils or Volcanogenous Regosols are generally
distributed. The texture of the deposited volcanic ash typically changes according to the distance from volcanoes.
(3) Soil distributions
The cultivated area of Hokkaido is approximately
1,146,000 ha (2016 estimate). This accounts for 13.7% of
the total area of Hokkaido (8,342,000 ha) and for 25.6% of
the total cultivated area in Japan. The area of paddy field is
relatively low, at 223,000 ha, as is the net area of cultivated
paddy rice, at 105,000 ha. The area of upland field is
924,000 ha and is composed of ordinary upland field
(416,000 ha), orchard land (3000 ha), and grassland
(505,000 ha).
A 1:200,000 soil map, which includes non-cultivated
area, was published by the Land Bureau (National Land
Agency 1975–1979). However, in this map, the soil classification system is not consolidated for different land uses.
Kanda et al. (2016) attempted to reclassify soil names under
a single new soil classification system. Based on this system,
Andosols occupy 43.1% of Hokkaido, brown forest soils
30.2%, and fulvic soils 11.1%. A 1:50,000 soil map of
cultivated land was published in 1959–1979 based on as part
of a national soil survey project and is widely used. Kanda
et al. (2017) reclassified the original data from this map into
the new soil classification system and reported that Andosols
occupied 40.9% of the total cultivated area of Hokkaido and
Fulvic soils 28.7%. Soil distribution areas can now be
determined based on the new Soil Classification System of
Japan (Fifth Committee for Soil Classification and Nomenclature of the Japanese Society of Pedology, 2017)
(Table 5.1). Local governmental engineers use four divided
soil types, namely volcanic ash soils, terrace soils, lowland
soils, and peat soils, when developing new fertility techniques and leading farmers. The volcanic ash soil type in
Hokkaido includes Volcanogenous Regosols.213. These
relationships are shown in Table 5.1.
(4) Soil improvement
The soil drying period is shorter in Hokkaido than in the
other areas of Japan. This fact means that upland crops can
be cultivated without irrigation and that there is no risk of
salt accumulation in surface soils. However, excessive
rainfall on poorly drained soils usually results in a high
water table or periodic flooding. This results in poor soil
aeration, which may reduce crop growth. Therefore, drainage has been the most important countermeasure for upland
crop fields. In paddy fields, drainage is important for
producing high-quality rice or cultivating upland crops
(under the paddy upland rotation). For these purposes,
underground drainage pipes or open-channel drainage have
been set in many fields for a long time. Thus, poorly drained
soils have been converted to well-drained soils.
Soil improvement projects have been conducted in order
to increase soil productivity. One major improvement program, involving soil-dressing, was carried out for paddy
fields, which were covered by peat soils. After the 1980s,
soil-dressing was widely carried out in upland fields with the
objective of improving soil character—for example,
increasing the depth of the plow layer or changing soil
texture. More recently, soil-dressing has been carried out by
national or local governmental land improvement projects.
Mixing tillage, which mixed surface with subsoil, has been
carried out in volcanic ash soil. Gravel removal has been
performed in stony soils, which cover 12% of the cultivated
area in Hokkaido. Subsoil breaking has also been carried
out. Hardpan has formed directly under a surface layer with
plowing or rotary tillage operations. Calcium or phosphate
application has been continued. The inherent soil properties
have been changed due to these improvement actions, now
that appropriate fertilizations can be chosen based on the soil
properties of individual fields.
5.2 Paddy Fields
5.2.1 Paddy Soil
(1) Soil groups and characteristics of paddy fields in
Hokkaido
Of the total area of paddy fields in Hokkaido (ca.
223,000 ha), about 80% is located in the Ishikari, Sorachi,
and Kamikawa areas. Gray Fluvic soils are most widely
distributed in these areas, followed in order by Gley Fluvic
soils, Peat soils, and Brown Fluvic soils. These four soil
groups account for 80% of total paddy field area.
Gley Fluvic soils are mainly distributed in low wetlands
and swampy areas of river basins, which are common in the
Ishikari, Sorachi, and Kamikawa areas. These areas are
characterized by a high groundwater level, clayey soils, and
extremely low permeability. Gray Fluvic soils have a lower
groundwater level than Gley Fluvic soils and slightly inferior
drainage. These soils are mainly distributed in the middle
and lower reaches of river basins and are common in the
Sorachi and Kamikawa areas. Brown Fluvic soils are widely
distributed in Hokkaido, mainly in natural levees and alluvial fans. These soils have good drainage, low groundwater
level, and more oxidized condition. Brown Fluvic soils are
widely used as uplands and grasslands, and in the Kamikawa
138
T. Nakatsuji et al.
volcanic ash soils or Volcanogenous Regosols are generally
distributed. The texture of the deposited volcanic ash typically changes according to the distance from volcanoes.
(3) Soil distributions
The cultivated area of Hokkaido is approximately
1,146,000 ha (2016 estimate). This accounts for 13.7% of
the total area of Hokkaido (8,342,000 ha) and for 25.6% of
the total cultivated area in Japan. The area of paddy field is
relatively low, at 223,000 ha, as is the net area of cultivated
paddy rice, at 105,000 ha. The area of upland field is
924,000 ha and is composed of ordinary upland field
(416,000 ha), orchard land (3000 ha), and grassland
(505,000 ha).
A 1:200,000 soil map, which includes non-cultivated
area, was published by the Land Bureau (National Land
Agency 1975–1979). However, in this map, the soil classification system is not consolidated for different land uses.
Kanda et al. (2016) attempted to reclassify soil names under
a single new soil classification system. Based on this system,
Andosols occupy 43.1% of Hokkaido, brown forest soils
30.2%, and fulvic soils 11.1%. A 1:50,000 soil map of
cultivated land was published in 1959–1979 based on as part
of a national soil survey project and is widely used. Kanda
et al. (2017) reclassified the original data from this map into
the new soil classification system and reported that Andosols
occupied 40.9% of the total cultivated area of Hokkaido and
Fulvic soils 28.7%. Soil distribution areas can now be
determined based on the new Soil Classification System of
Japan (Fifth Committee for Soil Classification and Nomenclature of the Japanese Society of Pedology, 2017)
(Table 5.1). Local governmental engineers use four divided
soil types, namely volcanic ash soils, terrace soils, lowland
soils, and peat soils, when developing new fertility techniques and leading farmers. The volcanic ash soil type in
Hokkaido includes Volcanogenous Regosols.213. These
relationships are shown in Table 5.1.
(4) Soil improvement
The soil drying period is shorter in Hokkaido than in the
other areas of Japan. This fact means that upland crops can
be cultivated without irrigation and that there is no risk of
salt accumulation in surface soils. However, excessive
rainfall on poorly drained soils usually results in a high
water table or periodic flooding. This results in poor soil
aeration, which may reduce crop growth. Therefore, drainage has been the most important countermeasure for upland
crop fields. In paddy fields, drainage is important for
producing high-quality rice or cultivating upland crops
(under the paddy upland rotation). For these purposes,
underground drainage pipes or open-channel drainage have
been set in many fields for a long time. Thus, poorly drained
soils have been converted to well-drained soils.
Soil improvement projects have been conducted in order
to increase soil productivity. One major improvement program, involving soil-dressing, was carried out for paddy
fields, which were covered by peat soils. After the 1980s,
soil-dressing was widely carried out in upland fields with the
objective of improving soil character—for example,
increasing the depth of the plow layer or changing soil
texture. More recently, soil-dressing has been carried out by
national or local governmental land improvement projects.
Mixing tillage, which mixed surface with subsoil, has been
carried out in volcanic ash soil. Gravel removal has been
performed in stony soils, which cover 12% of the cultivated
area in Hokkaido. Subsoil breaking has also been carried
out. Hardpan has formed directly under a surface layer with
plowing or rotary tillage operations. Calcium or phosphate
application has been continued. The inherent soil properties
have been changed due to these improvement actions, now
that appropriate fertilizations can be chosen based on the soil
properties of individual fields.
5.2 Paddy Fields
5.2.1 Paddy Soil
(1) Soil groups and characteristics of paddy fields in
Hokkaido
Of the total area of paddy fields in Hokkaido (ca.
223,000 ha), about 80% is located in the Ishikari, Sorachi,
and Kamikawa areas. Gray Fluvic soils are most widely
distributed in these areas, followed in order by Gley Fluvic
soils, Peat soils, and Brown Fluvic soils. These four soil
groups account for 80% of total paddy field area.
Gley Fluvic soils are mainly distributed in low wetlands
and swampy areas of river basins, which are common in the
Ishikari, Sorachi, and Kamikawa areas. These areas are
characterized by a high groundwater level, clayey soils, and
extremely low permeability. Gray Fluvic soils have a lower
groundwater level than Gley Fluvic soils and slightly inferior
drainage. These soils are mainly distributed in the middle
and lower reaches of river basins and are common in the
Sorachi and Kamikawa areas. Brown Fluvic soils are widely
distributed in Hokkaido, mainly in natural levees and alluvial fans. These soils have good drainage, low groundwater
level, and more oxidized condition. Brown Fluvic soils are
widely used as uplands and grasslands, and in the Kamikawa
138
T. Nakatsuji et al.