suspended matter such as clay contained in surface drainage
water. Since the concentration of suspended matter tends to
increase as the degree of puddling increases, reducing the
degree of puddling is an effective way to prevent water
pollution. Furthermore, because the concentration of suspended matter tends to increase as the amount of water at the
time of puddling increases, saving water at the time of
puddling is also an effective means of mitigating clay
outflow.
Lime-based sewage sludge compost is classified as
ordinary fertilizer, but a fertilization standard (Urban Sewage
Sludge Agricultural Land Application Standard) is set
because such sewage sludge contains more heavy metals
than compost, and it easily increases the pH of soil. In
Hokkaido, composting is carried out, and the application
amount per hectare per year is indicated as 10 t dry matter
(Hokkaido Fertilizer Recommendations 2015; see Sect. 8.1).
In rice cultivation, if the application amount of lime-based
sewage sludge compost is 1 t ha
−1 or less, and the reduction
amount of chemical fertilizer nitrogen and phosphoric acid
per 1 ton of compost is about 5 kg, the yield and quality are
the same as in conventional rice cultivation and heavy metals
do not accumulate in white rice and soil (Sugikawa et al.
2009).
(2) Upland
(1) Soil management for mitigating greenhouse gas
emissions
In general, plowing or rotary tillage increases carbon dioxide
emissions by promoting the decomposition of soil organic
matter. For example, in Haplic Allophanic Andosols in a
5-year crop rotation system in Eastern Hokkaido, the
decreases in soil carbon content over 20 years for minimum
tillage (rotary tillage once in spring) and for conventional
tillage (rotary tillage twice in spring and plowing once in
autumn) were 1.04 Mg C ha
−1 y
−1 and 1.34 Mg C ha
−1 y
−1 ,
respectively. This shows that it is possible to mitigate the
degradation of soil organic matter by performing only
minimum tillage.
However, efforts to positively increase soil carbon stock
are also important. The application of organic materials
(including the incorporation of crop residue) is effective for
this purpose. Nakatsu and Tamura (2008) investigated the
effect of 30 years of continuous crop residue incorporation
and/or cattle manure application on the soil carbon content
of Haplic Allophanic Andosols under a 4-year crop rotation
system in Eastern Hokkaido. The results showed that soil
carbon content clearly decreased without the application of
crop residue and manure. In contrast, soil carbon content did
not change over the 30-year period with the application of
2.5 Mg ha
−1 of organic materials (dry matter basis), equivalent to 1 Mg C ha
−1 . Furthermore, soil carbon content
increased by 10% from its initial value with the application
of 5 Mg ha
−1 of organic materials, equivalent to 2 Mg C
ha
−1 . These results suggest that the annual decrease in soil
carbon is about 1 Mg C ha
−1 , which is nearly the same as the
value determined in the abovementioned case of 5-year
rotational cropping (1.04–1.34 Mg C ha
−1 ). We can also
estimate the ratio of the carbon accumulated in the soil to the
applied carbon to be about 8%, assuming that the organic
material was incorporated within the top 25 cm of the soil
and that the soil bulk density was 800 kg m
−3 .
Emissions of nitrous oxide associated with nitrogen fertilization and/or the incorporation of crop residues are
inevitably associated with crop production. Until recently, it
was considered difficult to balance the improvement of crop
productivity and nitrous oxide emission control at the same
time. Now, however, the following practical emission control techniques have been proposed.
One such technique is the use of controlled-release fertilizers such as coated fertilizer, chemically synthesized
slow-release fertilizer, and fertilizer containing nitrification
inhibitor (Akiyama et al. 2009). The application of these
fertilizers suppresses the rapid increase in soil solution nitrogen concentration, resulting in lower nitrous oxide emissions than when using usual chemical fertilizers.
Additionally, nitrous oxide emissions accompanied by
the incorporation of crop residues are mainly caused by
denitrification in anaerobic soil conditions. Accordingly,
basic soil management, such as ensuring drainage and air
permeability, is also effective for the control of nitrous oxide
emissions.
(2) Soil management for preventing nitrate pollution in
groundwater
As described in Sect. 5.7.1., the concept of “nitrogen environmental capacity” is used as an index for the risk assessment of
nitrate pollution of groundwater in agricultural lands in Hokkaido.
This value is also considered as the upper limit of nitrogen input to
keep the nitrate nitrogen concentration in groundwater below the
environmental criterion (10 mg NO 3 -N L
−1
).
In Hokkaido, the fertilization standards (see Sect. 8.1 for
details) for various crops are defined as the recommended
rate of fertilizer application for environmentally friendly
agriculture practice, and the observance of fertilization
standards ensures the prevention of nitrate pollution in
groundwater. If fertilization management based on the fertilization standards is practiced in upland fields, the risk of
nitrate pollution in groundwater is low, even without paying
special attention to the concept of nitrogen environmental
capacity (Suzuki et al. 2004).
166
T. Nakatsuji et al.
water. Since the concentration of suspended matter tends to
increase as the degree of puddling increases, reducing the
degree of puddling is an effective way to prevent water
pollution. Furthermore, because the concentration of suspended matter tends to increase as the amount of water at the
time of puddling increases, saving water at the time of
puddling is also an effective means of mitigating clay
outflow.
Lime-based sewage sludge compost is classified as
ordinary fertilizer, but a fertilization standard (Urban Sewage
Sludge Agricultural Land Application Standard) is set
because such sewage sludge contains more heavy metals
than compost, and it easily increases the pH of soil. In
Hokkaido, composting is carried out, and the application
amount per hectare per year is indicated as 10 t dry matter
(Hokkaido Fertilizer Recommendations 2015; see Sect. 8.1).
In rice cultivation, if the application amount of lime-based
sewage sludge compost is 1 t ha
−1 or less, and the reduction
amount of chemical fertilizer nitrogen and phosphoric acid
per 1 ton of compost is about 5 kg, the yield and quality are
the same as in conventional rice cultivation and heavy metals
do not accumulate in white rice and soil (Sugikawa et al.
2009).
(2) Upland
(1) Soil management for mitigating greenhouse gas
emissions
In general, plowing or rotary tillage increases carbon dioxide
emissions by promoting the decomposition of soil organic
matter. For example, in Haplic Allophanic Andosols in a
5-year crop rotation system in Eastern Hokkaido, the
decreases in soil carbon content over 20 years for minimum
tillage (rotary tillage once in spring) and for conventional
tillage (rotary tillage twice in spring and plowing once in
autumn) were 1.04 Mg C ha
−1 y
−1 and 1.34 Mg C ha
−1 y
−1 ,
respectively. This shows that it is possible to mitigate the
degradation of soil organic matter by performing only
minimum tillage.
However, efforts to positively increase soil carbon stock
are also important. The application of organic materials
(including the incorporation of crop residue) is effective for
this purpose. Nakatsu and Tamura (2008) investigated the
effect of 30 years of continuous crop residue incorporation
and/or cattle manure application on the soil carbon content
of Haplic Allophanic Andosols under a 4-year crop rotation
system in Eastern Hokkaido. The results showed that soil
carbon content clearly decreased without the application of
crop residue and manure. In contrast, soil carbon content did
not change over the 30-year period with the application of
2.5 Mg ha
−1 of organic materials (dry matter basis), equivalent to 1 Mg C ha
−1 . Furthermore, soil carbon content
increased by 10% from its initial value with the application
of 5 Mg ha
−1 of organic materials, equivalent to 2 Mg C
ha
−1 . These results suggest that the annual decrease in soil
carbon is about 1 Mg C ha
−1 , which is nearly the same as the
value determined in the abovementioned case of 5-year
rotational cropping (1.04–1.34 Mg C ha
−1 ). We can also
estimate the ratio of the carbon accumulated in the soil to the
applied carbon to be about 8%, assuming that the organic
material was incorporated within the top 25 cm of the soil
and that the soil bulk density was 800 kg m
−3 .
Emissions of nitrous oxide associated with nitrogen fertilization and/or the incorporation of crop residues are
inevitably associated with crop production. Until recently, it
was considered difficult to balance the improvement of crop
productivity and nitrous oxide emission control at the same
time. Now, however, the following practical emission control techniques have been proposed.
One such technique is the use of controlled-release fertilizers such as coated fertilizer, chemically synthesized
slow-release fertilizer, and fertilizer containing nitrification
inhibitor (Akiyama et al. 2009). The application of these
fertilizers suppresses the rapid increase in soil solution nitrogen concentration, resulting in lower nitrous oxide emissions than when using usual chemical fertilizers.
Additionally, nitrous oxide emissions accompanied by
the incorporation of crop residues are mainly caused by
denitrification in anaerobic soil conditions. Accordingly,
basic soil management, such as ensuring drainage and air
permeability, is also effective for the control of nitrous oxide
emissions.
(2) Soil management for preventing nitrate pollution in
groundwater
As described in Sect. 5.7.1., the concept of “nitrogen environmental capacity” is used as an index for the risk assessment of
nitrate pollution of groundwater in agricultural lands in Hokkaido.
This value is also considered as the upper limit of nitrogen input to
keep the nitrate nitrogen concentration in groundwater below the
environmental criterion (10 mg NO 3 -N L
−1
).
In Hokkaido, the fertilization standards (see Sect. 8.1 for
details) for various crops are defined as the recommended
rate of fertilizer application for environmentally friendly
agriculture practice, and the observance of fertilization
standards ensures the prevention of nitrate pollution in
groundwater. If fertilization management based on the fertilization standards is practiced in upland fields, the risk of
nitrate pollution in groundwater is low, even without paying
special attention to the concept of nitrogen environmental
capacity (Suzuki et al. 2004).
166
T. Nakatsuji et al.