rotation of paddy rice and upland crops. This rotation derives
from the “gentan” policy that was started in 1971. This
policy resulted in the conversion of paddy fields from rice
production to the production of other upland crops in order
to counteract the overproduction of rice. The improvement
of drainage was promoted to cultivate upland crops in wet
and semi-wet paddy field. In 2016, the proportion of paddy
fields in upland crop farming reached 52.8% in Hokkaido,
47.2% in Kyushu–Okinawa, 41.9% in Kinki–Chugoku–
Shikoku, 37.9% in Tohoku, 33% in Kanto–Koushinestu, and
31% in Tokai–Hokuriku.
The area of rice cropping field in Japan decreased from
3.13 million ha in 1961 to 1.48 million ha in 2016, a 52.8%
decrease. However, the harvest of brown rice decreased by
only 32.5%, from 11.9 to 8.04 million tons, since the yield
increased by 43%, from 3.80 to 5.44 tons/ha. The drying of
wet paddy field allows for appropriate field management and
could contribute to an increase in rice yield. Japan could
potentially produce 13.2 million tons of rice if all paddy
fields were used for rice cropping. Small paddy fields tend to
be merged into larger paddy fields (i.e., ! 4.4 ha). The yield
of brown rice is as low as 5.06 tons/ha in Kyushu, compared
with 5.67 tons/ha in Tohoku. Thus, Southern Japan tends to
have a lower brown rice yield, and a further reduction in
yield may occur due to global warming. Additionally, soil
compaction and a decrease in soil nitrogen levels are concerns, since paddy rice-upland rotational management
decreases levels of soil organic matter (Nira 2013).
(4) Upland crop fields
The total area of ordinary upland crop field is 1.15 million
ha, of which 36.2% is located in Hokkaido, 22.8% in Kanto–
Koushinetsu, 15.9% in Kyushu–Okinawa, 11.3% in Tohoku,
7.5% in Tokai–Hokuriku, and 6.2% in Kinki–Chugoku–
Shikoku. Of a total orchard area (287,000 ha), 27.6% is
distributed in Kinki–Chugoku–Shikoku, 20.9% in Kyushu–
Okinawa, 17.3% in Kanto–Koushinetsu, 16.7% in Tokai–
Hokuriku, 16.5% in Tohoku, and 1% in Hokkaido. On the
other hand, the total area of grazing field is 603,000 ha, of
which 83.7% is located in Hokkaido, 10% in Tohoku, 3.4%
in Kyushu–Okinawa, 1.5% in Kanto–Koushinetsu, and less
than 1% in Tokai–Hokuriku and Kinki–Chugoku–Shikoku.
The cropping area of wheat, which is a major upland
crop, fell from 0.65 million ha in 1961 to 0.21 million ha in
2016, a decrease of 67.8%. However, the yield increased by
49% in the same period, from 2.75 to 4.10 tons/ha. The
cropping area of soybean also fell, decreasing by 47.7%
from 0.29 to 0.15 million ha between 1961 and 2016, but the
yield of soybean increased by 17.7% in the same period,
from 1.35 to 1.59 tons/ha. The cropping area of vegetables
decreased by 15.7% between 1980 and 2016, falling to
0.56 million ha. The cropping area has also tended to
decrease for all upland crops.
On the other hand, the area of grazing field and upland crop
field for livestock increased from 0.15 million ha in 1996 to
0.74 ha in 2016. This was due to an increase of livestock
production; between 1961 and 2016, the numbers of dairy cattle
increased by 52.0%, beef cattle increased by 7.2%, pigs
increased by 258%, and egg-laying hens increased by 144%.
1.3.2 Potential of Crop Production
From 1959 to 1978, the Fundamental Soil Survey for Soil
Fertility Conservation was carried out by the prefectural
agricultural experiment stations under the Japanese Ministry of
Agriculture, Forestry and Fisheries, and cultivated soil maps at
a scale of 1:50,000 and evaluation maps of the potential of
crop production were developed. Soil surveys were performed
at 220,000 measurement points (one point in every 25 ha),
covering 2.89 million has of paddy field and 1.80 million ha
of upland crop field. This survey identified the physicochemical properties of soils that limited crop production. Out of
these survey points, 3323 points of representative soil profile
data, including descriptions of soil profile and physicochemical properties, were digitized (Oda et al. 1987). The Fundamental Soil Survey for Soil Fertility Conservation classified
the crop production potential into four grades:
Grade I: Soils have neither limitations nor hazards and have
high potential for crop production without any improvement;
Grade II: Soils have some limitations or hazards for crop
production. They require some improvement to achieve
good production;
Grade III: Soils have many limitations or hazards for crop
production. They require intensive improvement;
Grade IV: Soils have such great limitations or hazards that
they can hardly be used for agriculture. They require very
intensive improvement.
The factors used to define the soil grade were thickness of
topsoil (t), effective rooting depth of soil (d), gravel content
in topsoil (g), difficulty of plowing (p), saturated water
permeability (l), redox properties (r), wetness of land (w),
dryness of land ((w)), inherent fertility (f), available nutrients
(n), risk of growth disorders (i), risk of disaster (a), slope (s),
and erodibility (e).
Field improvement was performed to ameliorate the limiting factors for crop production. This improvement included
large-scale field improvement such as rezoning, flattening,
installation of underdrains, improvement of efficiency of
machine work and productivity, mineral soil dressing in
peatland, removal of gravel, drainage improvement, the
8
R. Hatano et al.
from the “gentan” policy that was started in 1971. This
policy resulted in the conversion of paddy fields from rice
production to the production of other upland crops in order
to counteract the overproduction of rice. The improvement
of drainage was promoted to cultivate upland crops in wet
and semi-wet paddy field. In 2016, the proportion of paddy
fields in upland crop farming reached 52.8% in Hokkaido,
47.2% in Kyushu–Okinawa, 41.9% in Kinki–Chugoku–
Shikoku, 37.9% in Tohoku, 33% in Kanto–Koushinestu, and
31% in Tokai–Hokuriku.
The area of rice cropping field in Japan decreased from
3.13 million ha in 1961 to 1.48 million ha in 2016, a 52.8%
decrease. However, the harvest of brown rice decreased by
only 32.5%, from 11.9 to 8.04 million tons, since the yield
increased by 43%, from 3.80 to 5.44 tons/ha. The drying of
wet paddy field allows for appropriate field management and
could contribute to an increase in rice yield. Japan could
potentially produce 13.2 million tons of rice if all paddy
fields were used for rice cropping. Small paddy fields tend to
be merged into larger paddy fields (i.e., ! 4.4 ha). The yield
of brown rice is as low as 5.06 tons/ha in Kyushu, compared
with 5.67 tons/ha in Tohoku. Thus, Southern Japan tends to
have a lower brown rice yield, and a further reduction in
yield may occur due to global warming. Additionally, soil
compaction and a decrease in soil nitrogen levels are concerns, since paddy rice-upland rotational management
decreases levels of soil organic matter (Nira 2013).
(4) Upland crop fields
The total area of ordinary upland crop field is 1.15 million
ha, of which 36.2% is located in Hokkaido, 22.8% in Kanto–
Koushinetsu, 15.9% in Kyushu–Okinawa, 11.3% in Tohoku,
7.5% in Tokai–Hokuriku, and 6.2% in Kinki–Chugoku–
Shikoku. Of a total orchard area (287,000 ha), 27.6% is
distributed in Kinki–Chugoku–Shikoku, 20.9% in Kyushu–
Okinawa, 17.3% in Kanto–Koushinetsu, 16.7% in Tokai–
Hokuriku, 16.5% in Tohoku, and 1% in Hokkaido. On the
other hand, the total area of grazing field is 603,000 ha, of
which 83.7% is located in Hokkaido, 10% in Tohoku, 3.4%
in Kyushu–Okinawa, 1.5% in Kanto–Koushinetsu, and less
than 1% in Tokai–Hokuriku and Kinki–Chugoku–Shikoku.
The cropping area of wheat, which is a major upland
crop, fell from 0.65 million ha in 1961 to 0.21 million ha in
2016, a decrease of 67.8%. However, the yield increased by
49% in the same period, from 2.75 to 4.10 tons/ha. The
cropping area of soybean also fell, decreasing by 47.7%
from 0.29 to 0.15 million ha between 1961 and 2016, but the
yield of soybean increased by 17.7% in the same period,
from 1.35 to 1.59 tons/ha. The cropping area of vegetables
decreased by 15.7% between 1980 and 2016, falling to
0.56 million ha. The cropping area has also tended to
decrease for all upland crops.
On the other hand, the area of grazing field and upland crop
field for livestock increased from 0.15 million ha in 1996 to
0.74 ha in 2016. This was due to an increase of livestock
production; between 1961 and 2016, the numbers of dairy cattle
increased by 52.0%, beef cattle increased by 7.2%, pigs
increased by 258%, and egg-laying hens increased by 144%.
1.3.2 Potential of Crop Production
From 1959 to 1978, the Fundamental Soil Survey for Soil
Fertility Conservation was carried out by the prefectural
agricultural experiment stations under the Japanese Ministry of
Agriculture, Forestry and Fisheries, and cultivated soil maps at
a scale of 1:50,000 and evaluation maps of the potential of
crop production were developed. Soil surveys were performed
at 220,000 measurement points (one point in every 25 ha),
covering 2.89 million has of paddy field and 1.80 million ha
of upland crop field. This survey identified the physicochemical properties of soils that limited crop production. Out of
these survey points, 3323 points of representative soil profile
data, including descriptions of soil profile and physicochemical properties, were digitized (Oda et al. 1987). The Fundamental Soil Survey for Soil Fertility Conservation classified
the crop production potential into four grades:
Grade I: Soils have neither limitations nor hazards and have
high potential for crop production without any improvement;
Grade II: Soils have some limitations or hazards for crop
production. They require some improvement to achieve
good production;
Grade III: Soils have many limitations or hazards for crop
production. They require intensive improvement;
Grade IV: Soils have such great limitations or hazards that
they can hardly be used for agriculture. They require very
intensive improvement.
The factors used to define the soil grade were thickness of
topsoil (t), effective rooting depth of soil (d), gravel content
in topsoil (g), difficulty of plowing (p), saturated water
permeability (l), redox properties (r), wetness of land (w),
dryness of land ((w)), inherent fertility (f), available nutrients
(n), risk of growth disorders (i), risk of disaster (a), slope (s),
and erodibility (e).
Field improvement was performed to ameliorate the limiting factors for crop production. This improvement included
large-scale field improvement such as rezoning, flattening,
installation of underdrains, improvement of efficiency of
machine work and productivity, mineral soil dressing in
peatland, removal of gravel, drainage improvement, the
8
R. Hatano et al.