with eluvial and illuvial horizons are formed. In Japanese
beech forest at elevations of 400–800 m, Brown Andosols
are formed. At similar elevations (400–600 m), Melanic
Andosols appear in areas strongly influenced by grass vegetation such as Miscanthus sinensis.
On the Shimokita Peninsula of Aomori Prefecture, different types of Andosols are formed depending on vegetation under similar climatic conditions (Takahashi et al.
1989). Brown Andosols are observed in the Japanese beech
forest, while Podzolic Andosols are formed under Thujopsis
dolabrata (cypress family; conifer), showing that this tree is
a strong podzolizer.
(ii) Distribution pattern of Allophanic Andosols and
Non-allophanic Andosols
Andosols can be divided into allophanic and non-allophanic
types based on their dominant clay mineralogical composition. In Allophanic Andosols, the clay fraction is dominated
by allophane and imogolite, and the potential for Al toxicity
is low. Conversely, in Non-allophanic Andosols, the clay
fraction is dominated by 2:1 minerals and soils are strongly
acidic. In the Tohoku region, Allophanic Andosols cover
856,000 ha, which is equal to 48% of the region’s total
Andosol land area, while Non-allophanic Andosols cover
935,000 ha, equal to 52% of its total Andosol land area.
Allophanic Andosols preferentially form in thick Holocene
tephra deposits, while Non-allophanic Andosols form in
areas with minimal Holocene tephra deposition (Saigusa and
Matsuyama 1998).
(2) Characteristics of Andosols and their use for
agriculture
(1) Soil properties relating to productivity
Andosols have several unique properties, such as thick black
horizons, high phosphorus retention, and low bulk density
(Shoji et al. 1985). The high humus content of Andosols is
associated with low bulk density and high water retention.
These unique physical properties provide good conditions
for upland crops. One of the most important factors limiting
crop growth in Andosols is their low phosphorus availability, which is due to the presence of high amounts of active
Al. Consequently, the heavy application of phosphate fertilizer is necessary to achieve a high yield of upland crops in
Andosols. Because Non-allophanic Andosols have large
amounts of exchangeable Al, they often cause symptoms of
serious aluminum toxicity in sensitive crops. It is important
that liming be carried out appropriately in both types of
Andosols, due to the soil acidity and the requirement of
calcium for crop nutrition.
(2) Utilization and management of Andosols
As already noted, Andosols are mainly used for upland crops
in Japan. The Towada area in Aomori Prefecture is a large
production center for root crops (Chinese yam, edible burdock, Japanese radish, and carrot). In particular, the Towada
region is Japan’s largest producer of Chinese yam (contributing about 40% of the total national production) and
edible burdock (about 35% of the total national production).
The reason that Towada is such a large producer of these
crops is mainly due to the soil properties of Allophanic
Andosols (i.e., a thick A horizon, low bulk density, friable
consistency, and weakly acidic pH). On the other hand, in
the Tsugaru area of Aomori Prefecture, apple is widely
cultivated in Allophanic Andosols, with the production
being the highest in Japan (about 60% of the total national
production of apples). Andosols are considered to be
unsuitable soils for apple cultivation due to their high water
retention, low temperature, and slow nitrogen mineralization
pattern; however, the development of a unique cultivation
technique for Andosols has made such cultivation possible
in the Tsugaru area (Sekiya 1982).
(3) Soil degradation by agriculture
In the Tohoku region, about 10% of total arable land is
estimated to be at risk of soil erosion. Soil erosion has been a
severe problem for crop growth in Andosols due to their low
bulk density. Therefore, several agronomic countermeasures,
such as minimum tillage, mixing of soil layers, improvement
of drainage, and application of compost, are recommended
for agriculture.
Since Allophanic Andosols are originally weakly acidic,
aluminum toxicity does not occur frequently in plants.
However, Allophanic Andosols can become strongly acidic
following the heavy application of chemical fertilizer.
Strongly acidic Allophanic Andosols with an accumulation
of acidic materials dissolves a part of the active Al fraction
in the soils, which causes Al toxicity and thereby leads to the
shallow rooting of Al-susceptible crops. Additionally, the
soil productivity of strongly acidic Allophanic Andosols is
lower than that of the original weakly acidic soil; for
example, the number of bacteria decreases (e.g., from
160 Â 10
6 cfu g
−1 for weakly acidic soil to 10 Â 10
6 cfu
g
−1 for strongly acidic soil) as do the levels of readily
mineralizable soil nitrogen (Matsuyama et al. 2005).
As the cultivation of specific crops continues, diseases
related to continuous cropping become a more severe
problem. In the Towada region of Aomori Prefecture (an
area of Allophanic Andosols), the production of Chinese
yam is reduced by Chinese yam root rot (Rhizoctonia rot)
even for only a few years of continuous cropping (Oikawa
6 Tohoku Region
193
beech forest at elevations of 400–800 m, Brown Andosols
are formed. At similar elevations (400–600 m), Melanic
Andosols appear in areas strongly influenced by grass vegetation such as Miscanthus sinensis.
On the Shimokita Peninsula of Aomori Prefecture, different types of Andosols are formed depending on vegetation under similar climatic conditions (Takahashi et al.
1989). Brown Andosols are observed in the Japanese beech
forest, while Podzolic Andosols are formed under Thujopsis
dolabrata (cypress family; conifer), showing that this tree is
a strong podzolizer.
(ii) Distribution pattern of Allophanic Andosols and
Non-allophanic Andosols
Andosols can be divided into allophanic and non-allophanic
types based on their dominant clay mineralogical composition. In Allophanic Andosols, the clay fraction is dominated
by allophane and imogolite, and the potential for Al toxicity
is low. Conversely, in Non-allophanic Andosols, the clay
fraction is dominated by 2:1 minerals and soils are strongly
acidic. In the Tohoku region, Allophanic Andosols cover
856,000 ha, which is equal to 48% of the region’s total
Andosol land area, while Non-allophanic Andosols cover
935,000 ha, equal to 52% of its total Andosol land area.
Allophanic Andosols preferentially form in thick Holocene
tephra deposits, while Non-allophanic Andosols form in
areas with minimal Holocene tephra deposition (Saigusa and
Matsuyama 1998).
(2) Characteristics of Andosols and their use for
agriculture
(1) Soil properties relating to productivity
Andosols have several unique properties, such as thick black
horizons, high phosphorus retention, and low bulk density
(Shoji et al. 1985). The high humus content of Andosols is
associated with low bulk density and high water retention.
These unique physical properties provide good conditions
for upland crops. One of the most important factors limiting
crop growth in Andosols is their low phosphorus availability, which is due to the presence of high amounts of active
Al. Consequently, the heavy application of phosphate fertilizer is necessary to achieve a high yield of upland crops in
Andosols. Because Non-allophanic Andosols have large
amounts of exchangeable Al, they often cause symptoms of
serious aluminum toxicity in sensitive crops. It is important
that liming be carried out appropriately in both types of
Andosols, due to the soil acidity and the requirement of
calcium for crop nutrition.
(2) Utilization and management of Andosols
As already noted, Andosols are mainly used for upland crops
in Japan. The Towada area in Aomori Prefecture is a large
production center for root crops (Chinese yam, edible burdock, Japanese radish, and carrot). In particular, the Towada
region is Japan’s largest producer of Chinese yam (contributing about 40% of the total national production) and
edible burdock (about 35% of the total national production).
The reason that Towada is such a large producer of these
crops is mainly due to the soil properties of Allophanic
Andosols (i.e., a thick A horizon, low bulk density, friable
consistency, and weakly acidic pH). On the other hand, in
the Tsugaru area of Aomori Prefecture, apple is widely
cultivated in Allophanic Andosols, with the production
being the highest in Japan (about 60% of the total national
production of apples). Andosols are considered to be
unsuitable soils for apple cultivation due to their high water
retention, low temperature, and slow nitrogen mineralization
pattern; however, the development of a unique cultivation
technique for Andosols has made such cultivation possible
in the Tsugaru area (Sekiya 1982).
(3) Soil degradation by agriculture
In the Tohoku region, about 10% of total arable land is
estimated to be at risk of soil erosion. Soil erosion has been a
severe problem for crop growth in Andosols due to their low
bulk density. Therefore, several agronomic countermeasures,
such as minimum tillage, mixing of soil layers, improvement
of drainage, and application of compost, are recommended
for agriculture.
Since Allophanic Andosols are originally weakly acidic,
aluminum toxicity does not occur frequently in plants.
However, Allophanic Andosols can become strongly acidic
following the heavy application of chemical fertilizer.
Strongly acidic Allophanic Andosols with an accumulation
of acidic materials dissolves a part of the active Al fraction
in the soils, which causes Al toxicity and thereby leads to the
shallow rooting of Al-susceptible crops. Additionally, the
soil productivity of strongly acidic Allophanic Andosols is
lower than that of the original weakly acidic soil; for
example, the number of bacteria decreases (e.g., from
160 Â 10
6 cfu g
−1 for weakly acidic soil to 10 Â 10
6 cfu
g
−1 for strongly acidic soil) as do the levels of readily
mineralizable soil nitrogen (Matsuyama et al. 2005).
As the cultivation of specific crops continues, diseases
related to continuous cropping become a more severe
problem. In the Towada region of Aomori Prefecture (an
area of Allophanic Andosols), the production of Chinese
yam is reduced by Chinese yam root rot (Rhizoctonia rot)
even for only a few years of continuous cropping (Oikawa
6 Tohoku Region
193