materials is desirable to reduce the risk of Cd contamination
in the case of lowering the levels of ponding water. The
conventional midseason drainage can cause deep cracks in
soil and prevent constant flooding; therefore, in this period,
saturated irrigation is recommended.
(2) Arsenic (As)
In the Kansai region, the agricultural specified areas of As
contamination (soluble As in 1 M HCl ! 15 mg kg
−1 ) are
distributed in two prefectures, over a total of 109 ha. All of
these are unspecified as of 2016, with soil dressing and other
countermeasures completed. Soil contamination with As is
not only related to mining activities; for example, marine
clays containing pyrite can also lead to As contamination
(Shimada 2009). Nevertheless, the main contaminations of
As in paddy fields are caused by mine minerals (e.g.,
arsenopyrite) and have been spread around basins through
river water in the past. About 68% of the abovementioned
specified areas are categorized to combined contamination
with Cd or copper (Cu), also administratively. In one area
near a mine, water restriction was operated in the past after
rice transplanting and was supposed to avoid physiological
disorders due to excess As (Jpn. Soc. Soil Sci. Plant Nutr.
(ed.) 1991)
(3) Copper (Cu)
In the Kansai region, the agricultural specified areas of Cu
contamination (soluble Cu in 0.1 M HCl ! 125 mg kg
−1 )
are distributed in four prefectures, covering a total area of
137 ha. The contamination is related to mining. The details
are as follows: simple contamination in two prefectures,
62 ha in total; combined contamination with Cd in one
prefecture, 67 ha in total. All of these are unspecified as of
2016, with countermeasure constructions completed. From
research in two prefectures, the decrease of brown rice yield
caused by physiological disorders was estimated to be
approximately 10% when the specified level of soil soluble
Cu in 0.1 M HCl was 125 mg kg
−1 . The replacement of
surface soil with subsoil and the application of liming
materials have been carried out as countermeasures against
excess Cu concentrations in soil (Jpn. Soc. Soil Sci. Plant
Nutr. (ed.) 1991).
(4) Nickel (Ni)
Serpentine soils are distributed in parts of the Chugoku and
Shikoku mountains. Weathering soils of serpentinite generally abound in Ni, which is isomorphously substituted with
magnesium (Mg) atoms in serpentine. Chromium (Cr) is also
accumulated by the same mechanism, but this element is
flocculated in heavy minerals, is not highly soluble, and is
relatively harmless to the growth of crops (Shishido and
Ishida 1999). In areas of serpentine soil, Dark Red soils
(Eutrosols), which obtain their color from heavy metal
compounds, show relatively high concentrations of Ni or Cr
(Morita et al. 1986). In the case of total Ni, the same trend
was observed in the serpentine soil areas in Hyogo Prefecture (Tsutaka 1989). In one of the field cases, where soybean
was cultivated in soils with excess levels of Ni (exchangeable Ni > 10 mg kg
−1 ), the yellowing or red spotting of
leaves was observed. These typical disorders were almost
eliminated after soil pH correction by the application of
liming minerals (Jpn. Soc. Soil Sci. Plant Nutr. (ed.) 1991)
9.3.3 Soil Management for Environmental Load
Reduction
1. Utilization of controlled-release fertilizer, such as
coated urea fertilizer
The single or multiple application of controlled-release fertilizer can be an option to supply the amount of nutrients that
is needed according to the various kind of crops and the
growing stage. The utilization of controlled-release fertilizer
is a very important tool for the reduction of environmental
load. Fertilizer consisting of coated urea, which makes the
temperature and relative humidity controlling factors of
fertilizer elution, is used extensively in paddy rice cropping
(i.e., under flooded conditions). A basal application technique of whole amount which is necessary to crop paddy rice
is established at many prefectures. This technique is combined with the technology to apply fertilizer in band shape
beside of the rows, which raises the fertilizer utilization rate
and also leads to labor saving and the reduction of application rate.
2. Technology of soil management for environmental
load reduction
(1) Paddy field
The technology used to reduce the environmental load from
paddy fields consists of two methods. One is shallow water
puddling, which involves plowing and irrigating the fields in
the shallow water state using the rice paddy harrow in order
to prevent compulsion drainage of ponded water. The other
one involves the plowing of rice straw in autumn to promote
the organization of mineralized nitrogen in soil in the
non-irrigated period. A study in Shiga Prefecture clearly
9 Kinki, Chugoku, and Shikoku Regions
323
in the case of lowering the levels of ponding water. The
conventional midseason drainage can cause deep cracks in
soil and prevent constant flooding; therefore, in this period,
saturated irrigation is recommended.
(2) Arsenic (As)
In the Kansai region, the agricultural specified areas of As
contamination (soluble As in 1 M HCl ! 15 mg kg
−1 ) are
distributed in two prefectures, over a total of 109 ha. All of
these are unspecified as of 2016, with soil dressing and other
countermeasures completed. Soil contamination with As is
not only related to mining activities; for example, marine
clays containing pyrite can also lead to As contamination
(Shimada 2009). Nevertheless, the main contaminations of
As in paddy fields are caused by mine minerals (e.g.,
arsenopyrite) and have been spread around basins through
river water in the past. About 68% of the abovementioned
specified areas are categorized to combined contamination
with Cd or copper (Cu), also administratively. In one area
near a mine, water restriction was operated in the past after
rice transplanting and was supposed to avoid physiological
disorders due to excess As (Jpn. Soc. Soil Sci. Plant Nutr.
(ed.) 1991)
(3) Copper (Cu)
In the Kansai region, the agricultural specified areas of Cu
contamination (soluble Cu in 0.1 M HCl ! 125 mg kg
−1 )
are distributed in four prefectures, covering a total area of
137 ha. The contamination is related to mining. The details
are as follows: simple contamination in two prefectures,
62 ha in total; combined contamination with Cd in one
prefecture, 67 ha in total. All of these are unspecified as of
2016, with countermeasure constructions completed. From
research in two prefectures, the decrease of brown rice yield
caused by physiological disorders was estimated to be
approximately 10% when the specified level of soil soluble
Cu in 0.1 M HCl was 125 mg kg
−1 . The replacement of
surface soil with subsoil and the application of liming
materials have been carried out as countermeasures against
excess Cu concentrations in soil (Jpn. Soc. Soil Sci. Plant
Nutr. (ed.) 1991).
(4) Nickel (Ni)
Serpentine soils are distributed in parts of the Chugoku and
Shikoku mountains. Weathering soils of serpentinite generally abound in Ni, which is isomorphously substituted with
magnesium (Mg) atoms in serpentine. Chromium (Cr) is also
accumulated by the same mechanism, but this element is
flocculated in heavy minerals, is not highly soluble, and is
relatively harmless to the growth of crops (Shishido and
Ishida 1999). In areas of serpentine soil, Dark Red soils
(Eutrosols), which obtain their color from heavy metal
compounds, show relatively high concentrations of Ni or Cr
(Morita et al. 1986). In the case of total Ni, the same trend
was observed in the serpentine soil areas in Hyogo Prefecture (Tsutaka 1989). In one of the field cases, where soybean
was cultivated in soils with excess levels of Ni (exchangeable Ni > 10 mg kg
−1 ), the yellowing or red spotting of
leaves was observed. These typical disorders were almost
eliminated after soil pH correction by the application of
liming minerals (Jpn. Soc. Soil Sci. Plant Nutr. (ed.) 1991)
9.3.3 Soil Management for Environmental Load
Reduction
1. Utilization of controlled-release fertilizer, such as
coated urea fertilizer
The single or multiple application of controlled-release fertilizer can be an option to supply the amount of nutrients that
is needed according to the various kind of crops and the
growing stage. The utilization of controlled-release fertilizer
is a very important tool for the reduction of environmental
load. Fertilizer consisting of coated urea, which makes the
temperature and relative humidity controlling factors of
fertilizer elution, is used extensively in paddy rice cropping
(i.e., under flooded conditions). A basal application technique of whole amount which is necessary to crop paddy rice
is established at many prefectures. This technique is combined with the technology to apply fertilizer in band shape
beside of the rows, which raises the fertilizer utilization rate
and also leads to labor saving and the reduction of application rate.
2. Technology of soil management for environmental
load reduction
(1) Paddy field
The technology used to reduce the environmental load from
paddy fields consists of two methods. One is shallow water
puddling, which involves plowing and irrigating the fields in
the shallow water state using the rice paddy harrow in order
to prevent compulsion drainage of ponded water. The other
one involves the plowing of rice straw in autumn to promote
the organization of mineralized nitrogen in soil in the
non-irrigated period. A study in Shiga Prefecture clearly
9 Kinki, Chugoku, and Shikoku Regions
323