and the risk of nitrous oxide generation is therefore relatively
low. The reduction of the amount of applied fertilizer is an
effective countermeasure to nitrous oxide generation. In the
Kansai region, farmland is often over-fertilized, and as a
result, in 13 of the 15 prefectures in the region, there are
reports of fields holding nutrients that exceed the improvement target of the field (Council of Investigation for Soil
Conservation 2012).
2. Nitrate leaching
(1) Concentration of nitrate–nitrogen in groundwater
Nitrate–nitrogen and nitrite–nitrogen (hereinafter referred to
as nitrate) were added to the environmental quality standards
for water pollution (items for protecting human health and
living environment) in 1999; the standard value was set at
10 mg L
−1 .
Since the addition of the nitrate standards, the national
government and local governments have conducted the
monitoring of nitrate, and their findings have shown that the
detected concentration is especially high in groundwater.
Although the number of wells exceeding the standard values
had been increasing until peaking in 2010, it subsequently
decreased slightly for five consecutive years (Ministry of the
Environment, 2016a). Looking at the results for 2015 in the
Kansai region, in a general monitoring survey with 589
measurement points, excess levels of nitrate were detected
for 13 points (2.2%). Additionally, in a continuous monitoring survey with 202 measurement points, excess levels
were detected for 60 points (29.7%). Nationwide, excess
levels of nitrate were detected in 3.5% of measurement
points in the general monitoring survey and in 43.8% in the
continuous survey. Although it is not possible to simply
compare both surveys, the Kansai region seems to have
relatively low concentrations of nitrate. As mentioned above,
one of the reasons for this is considered to be the fact that the
proportion of paddy fields is 75% of total agricultural land
and that of upland field is 25%. However, in the coastal area
of the Seto Inland Sea, excess levels of nitrate are high. In
this area, annual rainfall is as low as 1300 mm, many storage
reservoirs are built, and water is repeatedly used. Another
reason would be that, as in the coastal area of the Seto Inland
Sea, there are many Gray Fluvic soils with good drainage,
paddy fields are mainly well drained, and the cultivated area
of vegetables and fruit trees is large.
(2) Techniques for suppressing nitrate leaching
With regard to the type of fertilizer, effect-controlled fertilization that can control the amount of elution to match the
growing season of crops has been developed, and technology to increase nitrogen utilization rate has been introduced.
In the fertilizer application method, side-dressing rice
transplanter and simultaneous ridge-forming fertilization
machines for the cultivation of vegetables (lettuce (Lactuca
sativa), cabbage (Brassica oleracea var. capitata), etc.) have
been developed. These are technologies to allow the
reduction of fertilizer application by increasing the absorptivity of fertilizer nitrogen by the topical application of fertilizer with controlled fertilization to the root area along with
labor saving.
With the fertilization reduction technology based on the
cropping system, the use of green manure is also increasing.
Green manure plants of the legume family (e.g., hairy vetch
[Vicia villosa] and Chinese milk vetch [Astragalus sinicus])
provide nitrogen fertilization and can thus allow the reduction of fertilization, and additionally improve the physicochemical properties of soil by replenishing organic matter.
Nitrate leaching is promoted when the field becomes bare
ground in winter, and nitrate leaching can be suppressed by
absorbing nitrogen to green manure.
3. Noxious chemicals
In the Kansai region, noxious chemicals related to the contamination of agricultural soils include cadmium (Cd),
copper (Cu), and arsenic (As) as specified noxious matter,
and nickel (Ni) which is abundant in serpentine soils. The
administrative specified situations of soil contamination and
its area are based on the data of the Ministry of Environment
(Ministry of the Environment 2016b).
(1) Cadmium (Cd)
In the Kansai region, the main areas of Cd contamination
are caused by the inflow of mine wastewater. Such areas are
distributed in three prefectures, and to date cover a total of
316 ha. All of these were unspecified as of 2016, with
countermeasures such as soil dressing and the implementation of sand settling channels (to prevent repollution by
bottom materials) completed.
In the case of paddy rice, the basic method for avoiding
Cd uptake by rice plants is constant flooding for three weeks
before and after the heading date (six weeks in total). For
example, in excessively permeable paddy fields (water
requirement in depth ! 30 mm day
−1 ), in the main
Cd-contaminated area of Hyogo Prefecture (Hyogo Prefecture, 1987), careful water management is required so as not
to exposure the soil surface. In paddy fields with mediumand coarse-textured gravelly soil, soils can become gradually
acidified. Soil pH correction by the application of liming
322
J. Yanai et al.
low. The reduction of the amount of applied fertilizer is an
effective countermeasure to nitrous oxide generation. In the
Kansai region, farmland is often over-fertilized, and as a
result, in 13 of the 15 prefectures in the region, there are
reports of fields holding nutrients that exceed the improvement target of the field (Council of Investigation for Soil
Conservation 2012).
2. Nitrate leaching
(1) Concentration of nitrate–nitrogen in groundwater
Nitrate–nitrogen and nitrite–nitrogen (hereinafter referred to
as nitrate) were added to the environmental quality standards
for water pollution (items for protecting human health and
living environment) in 1999; the standard value was set at
10 mg L
−1 .
Since the addition of the nitrate standards, the national
government and local governments have conducted the
monitoring of nitrate, and their findings have shown that the
detected concentration is especially high in groundwater.
Although the number of wells exceeding the standard values
had been increasing until peaking in 2010, it subsequently
decreased slightly for five consecutive years (Ministry of the
Environment, 2016a). Looking at the results for 2015 in the
Kansai region, in a general monitoring survey with 589
measurement points, excess levels of nitrate were detected
for 13 points (2.2%). Additionally, in a continuous monitoring survey with 202 measurement points, excess levels
were detected for 60 points (29.7%). Nationwide, excess
levels of nitrate were detected in 3.5% of measurement
points in the general monitoring survey and in 43.8% in the
continuous survey. Although it is not possible to simply
compare both surveys, the Kansai region seems to have
relatively low concentrations of nitrate. As mentioned above,
one of the reasons for this is considered to be the fact that the
proportion of paddy fields is 75% of total agricultural land
and that of upland field is 25%. However, in the coastal area
of the Seto Inland Sea, excess levels of nitrate are high. In
this area, annual rainfall is as low as 1300 mm, many storage
reservoirs are built, and water is repeatedly used. Another
reason would be that, as in the coastal area of the Seto Inland
Sea, there are many Gray Fluvic soils with good drainage,
paddy fields are mainly well drained, and the cultivated area
of vegetables and fruit trees is large.
(2) Techniques for suppressing nitrate leaching
With regard to the type of fertilizer, effect-controlled fertilization that can control the amount of elution to match the
growing season of crops has been developed, and technology to increase nitrogen utilization rate has been introduced.
In the fertilizer application method, side-dressing rice
transplanter and simultaneous ridge-forming fertilization
machines for the cultivation of vegetables (lettuce (Lactuca
sativa), cabbage (Brassica oleracea var. capitata), etc.) have
been developed. These are technologies to allow the
reduction of fertilizer application by increasing the absorptivity of fertilizer nitrogen by the topical application of fertilizer with controlled fertilization to the root area along with
labor saving.
With the fertilization reduction technology based on the
cropping system, the use of green manure is also increasing.
Green manure plants of the legume family (e.g., hairy vetch
[Vicia villosa] and Chinese milk vetch [Astragalus sinicus])
provide nitrogen fertilization and can thus allow the reduction of fertilization, and additionally improve the physicochemical properties of soil by replenishing organic matter.
Nitrate leaching is promoted when the field becomes bare
ground in winter, and nitrate leaching can be suppressed by
absorbing nitrogen to green manure.
3. Noxious chemicals
In the Kansai region, noxious chemicals related to the contamination of agricultural soils include cadmium (Cd),
copper (Cu), and arsenic (As) as specified noxious matter,
and nickel (Ni) which is abundant in serpentine soils. The
administrative specified situations of soil contamination and
its area are based on the data of the Ministry of Environment
(Ministry of the Environment 2016b).
(1) Cadmium (Cd)
In the Kansai region, the main areas of Cd contamination
are caused by the inflow of mine wastewater. Such areas are
distributed in three prefectures, and to date cover a total of
316 ha. All of these were unspecified as of 2016, with
countermeasures such as soil dressing and the implementation of sand settling channels (to prevent repollution by
bottom materials) completed.
In the case of paddy rice, the basic method for avoiding
Cd uptake by rice plants is constant flooding for three weeks
before and after the heading date (six weeks in total). For
example, in excessively permeable paddy fields (water
requirement in depth ! 30 mm day
−1 ), in the main
Cd-contaminated area of Hyogo Prefecture (Hyogo Prefecture, 1987), careful water management is required so as not
to exposure the soil surface. In paddy fields with mediumand coarse-textured gravelly soil, soils can become gradually
acidified. Soil pH correction by the application of liming
322
J. Yanai et al.