show the largest distribution area (47%), followed by
Andosols (29%). Fluvic soils are mainly used as paddy field
(71%). About half of the uplands and meadow fields are
covered by Andosols. Both Fluvic soils and Andosols are
mainly developed on flat plains, and these areas are suitable
for cultivation. Brown forest soils cover only 8% of the total
cultivated area and are mainly utilized as orchard. Despite
the small distribution area of organic soils and stagnic soils
(Table 2.2 in Chapter 2) in Japan, both of these soil great
groups are well utilized as paddy fields.
3.2.3 Soil Threats in Japanese Agricultural Land
Agricultural soil is not only an important resource that
secures food supply, but also provides several ecological
services. However, the functions of agricultural soils are
threatened by a wide range of processes, and a number of
soil threats have been identified in Japan. In Chaps. 5–10,
there are several reports about the current status and trends in
the condition of agricultural soil in each region of Japan.
Nutrient imbalance, SOM decline, heavy metal contamination, and soil sealing are reported as major threats to Japanese agricultural soils.
(1) Nutrient Imbalance
Nutrient imbalance has been one of the most important
issues for sustainable agriculture in Japan. The MAFF
revised the Fundamental Guidelines for Fertility Improvement in 2008. These guidelines pointed out that the excessive application of nitrogen and phosphorus fertilizers was
having a significant environmental impact. Today, the surface soil nitrogen (N) and phosphorus (P) balance has been
improved in Japanese cultivated land (Mishima et al. 2009,
2010). The application of chemical fertilizer declined consistently from 1985 to 2005, while the rate of application of
livestock manure peaked in 1990 and declined thereafter.
Crop production remained constant during this period.
Between 1985 and 2005, the surplus N and P (positive value
of soil surface N balance) declined from 89.9 to 49.3 kg
N ha
−1 and from 153 to 105 kg P ha
−1 , respectively (Mishima et al. 2009, 2010). However, this trend was not consistent at the regional level because organic amendment
application was largely affected by the distribution of livestock excreta (Mishima et al. 2009) and soil types (Leon
et al. 2012). High surplus P and low crop P-uptake compared
with N and P input for crop production could be reduced,
thereby reducing negative environmental effects such as the
eutrophication of soil and water and conserving limited P
resources. According to the Basic Soil-Environmental
Monitoring Project, there was excess soil Ca in paddy
fields, upland fields, and orchard fields during 1979–1998
(Ministry of Agriculture, Forestry and Fishery 2008); however, the soil Mg deficit gradually increased in this period.
The balance of Ca and Mg has thus been getting worse in
Japanese cultivated land. Moreover, the soil pH of paddy
fields gradually decreased from 5.8 to 5.7 during 1979–1998
(Ministry of Agriculture, Forestry and Fishery 2008).
(2) Soil Organic Matter Decline
Soil organic matter (SOM) decline has been widely recognized
as a major threat to world soil resources, because of the vital
role played by the organic material in many soil functions, such
as food production and the terrestrial reservoir of carbon
(Intergovernmental Technical Panel on Soils 2015). The
problem of SOM decline has thus become a hot topic in soil
surveys in the last decade. Because SOC in Japanese cultivated
land has been monitored since 1979, this data can provide very
valuable information on this topic. A cultivated soil monitoring
project named “Basic Soil-Environmental Monitoring” in
Japan has repeated monitoring at five-year intervals for about
20,000 fixed points. The measured rate of changes in the total
SOC stock evaluated by the monitoring approach was
2.3 Tg C yr
−1 from 1979 to 1989, indicating that SOC
increased in cultivated land. However, this approach also
detected a loss of SOC, at a rate of −2.3 Tg C yr
−1
, from 1989
to 1998. During this period, the cultivated land area decreased
from 5.4 to 5.0 million ha and the soil carbon content of arable
land gradually increased from 88 to 90 t C ha
−1
. These results
indicate that the decline of SOC stock in Japanese cultivated
land was mainly caused by the decrease of cultivated land area.
(3) Soil Contamination
In Japan, rapid industrialization during the 1960s led to
pollution of arable soil by heavy metals such as cadmium
(Cd), copper (Cu), and arsenic (As). There were four main
sources of heavy metal pollution for arable land, namely
mining activity, factories and incinerators, fertilizers, and
precipitation and irrigation water (Makino et al. 2010). In
1970, the Japanese government enacted the Agricultural
Land Soil Pollution Prevention Law to regulate heavy metal
pollution. The Agricultural Land Soil Pollution Prevention
Law designated Cd, As, and Cu as hazardous substances to
be regulated. The allowable limit of Cd was set as the Cd
concentration in rice grains (1 mg kg
−1
), and the allowable
limits of As and Cu were set to 15 (1 M HCl soluble) and
125 (0.1 M HCl soluble) mg kg soil
−1
, respectively. The
amount of bioavailable Cd in soil is affected by many factors,
so setting an allowable soil Cd content is impractical (Asami
3 Soil Classification and Distribution
67
Andosols (29%). Fluvic soils are mainly used as paddy field
(71%). About half of the uplands and meadow fields are
covered by Andosols. Both Fluvic soils and Andosols are
mainly developed on flat plains, and these areas are suitable
for cultivation. Brown forest soils cover only 8% of the total
cultivated area and are mainly utilized as orchard. Despite
the small distribution area of organic soils and stagnic soils
(Table 2.2 in Chapter 2) in Japan, both of these soil great
groups are well utilized as paddy fields.
3.2.3 Soil Threats in Japanese Agricultural Land
Agricultural soil is not only an important resource that
secures food supply, but also provides several ecological
services. However, the functions of agricultural soils are
threatened by a wide range of processes, and a number of
soil threats have been identified in Japan. In Chaps. 5–10,
there are several reports about the current status and trends in
the condition of agricultural soil in each region of Japan.
Nutrient imbalance, SOM decline, heavy metal contamination, and soil sealing are reported as major threats to Japanese agricultural soils.
(1) Nutrient Imbalance
Nutrient imbalance has been one of the most important
issues for sustainable agriculture in Japan. The MAFF
revised the Fundamental Guidelines for Fertility Improvement in 2008. These guidelines pointed out that the excessive application of nitrogen and phosphorus fertilizers was
having a significant environmental impact. Today, the surface soil nitrogen (N) and phosphorus (P) balance has been
improved in Japanese cultivated land (Mishima et al. 2009,
2010). The application of chemical fertilizer declined consistently from 1985 to 2005, while the rate of application of
livestock manure peaked in 1990 and declined thereafter.
Crop production remained constant during this period.
Between 1985 and 2005, the surplus N and P (positive value
of soil surface N balance) declined from 89.9 to 49.3 kg
N ha
−1 and from 153 to 105 kg P ha
−1 , respectively (Mishima et al. 2009, 2010). However, this trend was not consistent at the regional level because organic amendment
application was largely affected by the distribution of livestock excreta (Mishima et al. 2009) and soil types (Leon
et al. 2012). High surplus P and low crop P-uptake compared
with N and P input for crop production could be reduced,
thereby reducing negative environmental effects such as the
eutrophication of soil and water and conserving limited P
resources. According to the Basic Soil-Environmental
Monitoring Project, there was excess soil Ca in paddy
fields, upland fields, and orchard fields during 1979–1998
(Ministry of Agriculture, Forestry and Fishery 2008); however, the soil Mg deficit gradually increased in this period.
The balance of Ca and Mg has thus been getting worse in
Japanese cultivated land. Moreover, the soil pH of paddy
fields gradually decreased from 5.8 to 5.7 during 1979–1998
(Ministry of Agriculture, Forestry and Fishery 2008).
(2) Soil Organic Matter Decline
Soil organic matter (SOM) decline has been widely recognized
as a major threat to world soil resources, because of the vital
role played by the organic material in many soil functions, such
as food production and the terrestrial reservoir of carbon
(Intergovernmental Technical Panel on Soils 2015). The
problem of SOM decline has thus become a hot topic in soil
surveys in the last decade. Because SOC in Japanese cultivated
land has been monitored since 1979, this data can provide very
valuable information on this topic. A cultivated soil monitoring
project named “Basic Soil-Environmental Monitoring” in
Japan has repeated monitoring at five-year intervals for about
20,000 fixed points. The measured rate of changes in the total
SOC stock evaluated by the monitoring approach was
2.3 Tg C yr
−1 from 1979 to 1989, indicating that SOC
increased in cultivated land. However, this approach also
detected a loss of SOC, at a rate of −2.3 Tg C yr
−1
, from 1989
to 1998. During this period, the cultivated land area decreased
from 5.4 to 5.0 million ha and the soil carbon content of arable
land gradually increased from 88 to 90 t C ha
−1
. These results
indicate that the decline of SOC stock in Japanese cultivated
land was mainly caused by the decrease of cultivated land area.
(3) Soil Contamination
In Japan, rapid industrialization during the 1960s led to
pollution of arable soil by heavy metals such as cadmium
(Cd), copper (Cu), and arsenic (As). There were four main
sources of heavy metal pollution for arable land, namely
mining activity, factories and incinerators, fertilizers, and
precipitation and irrigation water (Makino et al. 2010). In
1970, the Japanese government enacted the Agricultural
Land Soil Pollution Prevention Law to regulate heavy metal
pollution. The Agricultural Land Soil Pollution Prevention
Law designated Cd, As, and Cu as hazardous substances to
be regulated. The allowable limit of Cd was set as the Cd
concentration in rice grains (1 mg kg
−1
), and the allowable
limits of As and Cu were set to 15 (1 M HCl soluble) and
125 (0.1 M HCl soluble) mg kg soil
−1
, respectively. The
amount of bioavailable Cd in soil is affected by many factors,
so setting an allowable soil Cd content is impractical (Asami
3 Soil Classification and Distribution
67