processes since the eighth century. The presence of a
large-scale earthwork constructed through cut and banking
to create a residential area has also been confirmed. Disturbed soils through the earthwork have already started soil
formation processes affected by the development of vegetation. Accumulated humus in the soil profile indicates
vegetation succession by stable carbon isotope analysis,
indicating that soils on the earthworks were naturally processed over several centuries (Kawai et al. 2015).
Andosols have potentially occupied a large area in the
Tokyo metropolitan area. Soils taken by historical civil engineering works demonstrate typical andic properties, as indicated by a high content of non-crystalline minerals, high
phosphate retention, and high cation exchangeable capacity.
However, the physical properties of these soils have been
drastically altered, becoming highly compacted through civil
engineering processes. A larger amount of artifacts in the soils
is also a remarkable feature of their profile after anthropogenic
management and accordingly they are classified as humanmade soils in most classification systems. It can be recognized
from the soil profiles that even the soils under greenery areas
are strongly affected by large-scale civil engineering.
(3) Soils on human-made islands in the Tokyo Bay
The Tokyo Bay area has already been fully occupied by
human-made islands, except for in the sea lane, which is
used for transportation. The extension of the sea shore along
the Tokyo Bay had already been started in the Edo period as
waste landfill. The reclamation of excessively growing urban
waste for management purposes has been frequently conducted during the period of high economic growth between
late 50s and 1973 when Oil shock occurred in Japan. The
human-made islands in the bay area have been used for
industrial and urban purposes as well as for greenery areas.
The basements of the islands have been constructed with
domestic and construction wastes. Even in planting layers
for vegetation, construction debris is often present in large
amounts, which has resulted in soil alkalinization. Subsoils
are highly compacted by heavy machinery used to construct
the planting bases, which results in the limitation of vertical
root extension to shallow depths. Transported Andosols
have been dressed to create a planting surface horizon
accompanied by buried construction debris artifacts. Large
amounts of construction debris in the planting horizons
define the soil as Artifactual soil.
(4) Soils out of the scope of the soil classification
The center of the urbanized area in the Tokyo metropolitan
area has been highly saturated with buildings, which has
caused soils on the ground surface to become sealed as a
result of constructions such as roads and buildings. Soils
beneath constructions are outside the scope of the Japanese
Soil Classification System because they are sealed by technic
hard materials for a long time. Soils in green spaces along
road constructions, in open spaces between buildings, on
building walls and rooftops using tree pits, in planters with a
bottom, and in vertical hanging media for plants are not
classified using the system because in most cases those soils
are completely separated from the natural soil profile and
lack time for pedogenesis and material cycling. Urban areas
in the Tokyo metropolitan area are represented by white
spaces on the soil map.
7.3 Status and Changes of Agricultural Soil
Properties
7.3.1 Kanto Region
(1) Ibaraki Prefecture
There are 77,000 ha of paddy field in Ibaraki Prefecture, a
total of 70% of which are occupied by either Gley Fluvic
soils, Gray Fluvic soils, or Fluvic Paddy soils.
The distribution area of upland fields is 74,000 ha, the
main soils of which are Allophanic Andosols and Wet
Andosols.
(a) Actual condition of paddy soil
In recent years, a reduction in the application rate of organic
matter and improvements to the drainage systems in paddy
fields have resulted in a decline in the soil organic matter
content of these fields, and there are concerns that soil
productivity will decline as a result.
The current soil nutrient status in paddy fields in Ibaraki
Prefecture is characterized by a slightly high amount of
magnesium and potassium, although these are almost at the
same level as the prefectural recommendations. However,
the level of available nitrogen in the soils is decreasing, and
there is concern that farmers are less willing to maintain
levels of soil available nitrogen soil. The distribution frequencies of available phosphate and exchangeable potassium
in paddy soils are shown in Fig. 7.9. In Ibaraki Prefecture,
available phosphate was deficient in 23%, and in surplus in
14%, of paddy fields, while exchangeable potassium was
deficient in 4% and in surplus in 28%.
(b) Upland field soil
Allophanic Andosols are the main soil group in upland fields
in Ibaraki Prefecture. Liming is one of the most common soil
256
H. Sumida et al.
large-scale earthwork constructed through cut and banking
to create a residential area has also been confirmed. Disturbed soils through the earthwork have already started soil
formation processes affected by the development of vegetation. Accumulated humus in the soil profile indicates
vegetation succession by stable carbon isotope analysis,
indicating that soils on the earthworks were naturally processed over several centuries (Kawai et al. 2015).
Andosols have potentially occupied a large area in the
Tokyo metropolitan area. Soils taken by historical civil engineering works demonstrate typical andic properties, as indicated by a high content of non-crystalline minerals, high
phosphate retention, and high cation exchangeable capacity.
However, the physical properties of these soils have been
drastically altered, becoming highly compacted through civil
engineering processes. A larger amount of artifacts in the soils
is also a remarkable feature of their profile after anthropogenic
management and accordingly they are classified as humanmade soils in most classification systems. It can be recognized
from the soil profiles that even the soils under greenery areas
are strongly affected by large-scale civil engineering.
(3) Soils on human-made islands in the Tokyo Bay
The Tokyo Bay area has already been fully occupied by
human-made islands, except for in the sea lane, which is
used for transportation. The extension of the sea shore along
the Tokyo Bay had already been started in the Edo period as
waste landfill. The reclamation of excessively growing urban
waste for management purposes has been frequently conducted during the period of high economic growth between
late 50s and 1973 when Oil shock occurred in Japan. The
human-made islands in the bay area have been used for
industrial and urban purposes as well as for greenery areas.
The basements of the islands have been constructed with
domestic and construction wastes. Even in planting layers
for vegetation, construction debris is often present in large
amounts, which has resulted in soil alkalinization. Subsoils
are highly compacted by heavy machinery used to construct
the planting bases, which results in the limitation of vertical
root extension to shallow depths. Transported Andosols
have been dressed to create a planting surface horizon
accompanied by buried construction debris artifacts. Large
amounts of construction debris in the planting horizons
define the soil as Artifactual soil.
(4) Soils out of the scope of the soil classification
The center of the urbanized area in the Tokyo metropolitan
area has been highly saturated with buildings, which has
caused soils on the ground surface to become sealed as a
result of constructions such as roads and buildings. Soils
beneath constructions are outside the scope of the Japanese
Soil Classification System because they are sealed by technic
hard materials for a long time. Soils in green spaces along
road constructions, in open spaces between buildings, on
building walls and rooftops using tree pits, in planters with a
bottom, and in vertical hanging media for plants are not
classified using the system because in most cases those soils
are completely separated from the natural soil profile and
lack time for pedogenesis and material cycling. Urban areas
in the Tokyo metropolitan area are represented by white
spaces on the soil map.
7.3 Status and Changes of Agricultural Soil
Properties
7.3.1 Kanto Region
(1) Ibaraki Prefecture
There are 77,000 ha of paddy field in Ibaraki Prefecture, a
total of 70% of which are occupied by either Gley Fluvic
soils, Gray Fluvic soils, or Fluvic Paddy soils.
The distribution area of upland fields is 74,000 ha, the
main soils of which are Allophanic Andosols and Wet
Andosols.
(a) Actual condition of paddy soil
In recent years, a reduction in the application rate of organic
matter and improvements to the drainage systems in paddy
fields have resulted in a decline in the soil organic matter
content of these fields, and there are concerns that soil
productivity will decline as a result.
The current soil nutrient status in paddy fields in Ibaraki
Prefecture is characterized by a slightly high amount of
magnesium and potassium, although these are almost at the
same level as the prefectural recommendations. However,
the level of available nitrogen in the soils is decreasing, and
there is concern that farmers are less willing to maintain
levels of soil available nitrogen soil. The distribution frequencies of available phosphate and exchangeable potassium
in paddy soils are shown in Fig. 7.9. In Ibaraki Prefecture,
available phosphate was deficient in 23%, and in surplus in
14%, of paddy fields, while exchangeable potassium was
deficient in 4% and in surplus in 28%.
(b) Upland field soil
Allophanic Andosols are the main soil group in upland fields
in Ibaraki Prefecture. Liming is one of the most common soil
256
H. Sumida et al.