(Inoue 2016). Winter flooding is also expected as a management method for improving soil fertility that was depleted by paddy–upland rotation.
2. Present and future of soil science and plant nutrition
in Ishikawa Prefecture
According to “Ishikawa’s Visions for Food and Agriculture/
Agricultural Area”, Ishikawa Prefecture has been working
toward devising a system of low-cost rice cultivation technology, the efficient use of rice fields, environmentally
friendly agriculture, the multiple use and application of
biomass resources, and so on. Challenges specific to the area
of soil science and plant nutrition in these visions involve:
(1) reducing the fertilization cost by efficient fertilization in
response to the soil fertility; (2) solving the problem of poor
yield of soybean crops by increasing soil fertility; (3) establishing environmentally friendly farming technology; and
(4) promoting the utilization of unused organic materials
such as food residue. Researches corresponding to these
issues have been ongoing.
(1) Estimation of the amount of phosphate fertilizer in
rice cultivation reducible to the soil fertility
After soaring in 2008, the price of fertilizers has been kept
higher than pre-2008 levels, which has imposed a constraint
for farming. The price rise was particularly remarkable for
phosphate fertilizers, and a further rise is predicted due to the
declining resources for phosphate fertilizers. It is thus
essential to establish versatile and sustainable systems for
the utilization and circulation of unused organic materials
and to advance technologies for the reuse of phosphate from
wastes. Immediate measures are needed, as it will likely take
time to develop such new systems and technologies. One
possible immediate measure is to determine a minimum
amount of fertilizer application based on the soil fertility,
which could lead to a reduction in fertilizer expenditure. We
are studying the effects of reducing phosphate fertilizer
application in paddy rice production according to soil fertility, including its effect on the yield quality and quality of
rice.
The average Truog P content of the soils of Ishikawa
Prefecture is 156 mg kg
−1 dry soil; however, approximately
30% of the agricultural land in the prefecture has a Truog P
content of less than the target figure of 100 mg kg
−1 dry soil
that is set by the prefecture. An experiment is currently being
conducted in a rice field in the author’s research center, in
which the Truog P content was adjusted to 68 and
118 mg kg
−1 dry soil by adding calcium dihydrogen phosphate in order to study the effects of four rates of phosphate
fertilization on the growth of rice and soil phosphate fertility,
namely: 1) conventional (100 kg ha
−1 ); 2) corresponding to
the exploited amount (40 kg ha
−1 ); 3) corresponding to the
L-type fertilizer (20-10-10) application (20 kg ha
−1 ); and 4)
no phosphate fertilizer added.
The experiment will be conducted for five years and is
now in the second year. The rice yield in the first year was
comparable among the plots and treatments, suggesting that
a reduction of the amount of phosphate fertilizer application
is possible in soils that have phosphate levels equal to or
greater than that of the experimental field in this study, at
least for a single year. However, the soil phosphate fertility
decreased in the treatment with no phosphate fertilizer
application. The sound management of the phosphate fertilizer application should be developed by monitoring the
rice yield and soil phosphate content in the following years
(Table 8.1) (Kudo and Uno, 2012).
(2) Establishment and extension of environmentally
friendly agricultural technologies
In Ishikawa Prefecture, there are several closed water areas
with slow water circulation, and the deterioration of water
quality is regarded as an environmental problem. Kahokugata, the largest lagoon in the prefecture, is a representative
closed water area. The agricultural sector needs to contribute
to the improvement of water quality by reducing the load of
eutrophic substances. In Kahokugata lagoon, there is
reclaimed land where barley, soybean, paddy rice, lotus root,
watermelon, cabbage, and so on are planted, and we are
working on reducing the load of eutrophic substances in
these fields.
So far, for the barley and soybean crops, we have conducted field tests of environmental load-improving cultivation by side-dressing with slow-release fertilizers and have
demonstrated that the total amount of nitrogen discharged
from the field can be reduced by 34% compared with conventional cultivation (Fig. 8.13). In flooded rice cultivation,
we adopted the environmentally-friendly managements of
water and fertilizer: the shallow water-puddling and prevention of forced drainage to suppress discharge of turbid
water, and side-dressing fertilization with slow-release fertilizer. These managements successfully reduced the amount
of discharged total nitrogen and discharged total phosphate
by 23–39% and 34–39%, respectively (Fig. 8.14). We are
now testing the reducing effect of automatic water-saving
irrigation on the load of eutrophic substances in lotus root
cultivation. In the future, we plan to introduce machinery for
local fertilization in vegetable cultivation, which requires
more fertilizers than other crops, and to study the effectiveness of such technology for improving fertilizer utilization and reducing the amount of excess nitrogen loaded into
the lagoon (Uno et al. 2010).
8 Chubu Region (Hokuriku/Tokai)
285
2. Present and future of soil science and plant nutrition
in Ishikawa Prefecture
According to “Ishikawa’s Visions for Food and Agriculture/
Agricultural Area”, Ishikawa Prefecture has been working
toward devising a system of low-cost rice cultivation technology, the efficient use of rice fields, environmentally
friendly agriculture, the multiple use and application of
biomass resources, and so on. Challenges specific to the area
of soil science and plant nutrition in these visions involve:
(1) reducing the fertilization cost by efficient fertilization in
response to the soil fertility; (2) solving the problem of poor
yield of soybean crops by increasing soil fertility; (3) establishing environmentally friendly farming technology; and
(4) promoting the utilization of unused organic materials
such as food residue. Researches corresponding to these
issues have been ongoing.
(1) Estimation of the amount of phosphate fertilizer in
rice cultivation reducible to the soil fertility
After soaring in 2008, the price of fertilizers has been kept
higher than pre-2008 levels, which has imposed a constraint
for farming. The price rise was particularly remarkable for
phosphate fertilizers, and a further rise is predicted due to the
declining resources for phosphate fertilizers. It is thus
essential to establish versatile and sustainable systems for
the utilization and circulation of unused organic materials
and to advance technologies for the reuse of phosphate from
wastes. Immediate measures are needed, as it will likely take
time to develop such new systems and technologies. One
possible immediate measure is to determine a minimum
amount of fertilizer application based on the soil fertility,
which could lead to a reduction in fertilizer expenditure. We
are studying the effects of reducing phosphate fertilizer
application in paddy rice production according to soil fertility, including its effect on the yield quality and quality of
rice.
The average Truog P content of the soils of Ishikawa
Prefecture is 156 mg kg
−1 dry soil; however, approximately
30% of the agricultural land in the prefecture has a Truog P
content of less than the target figure of 100 mg kg
−1 dry soil
that is set by the prefecture. An experiment is currently being
conducted in a rice field in the author’s research center, in
which the Truog P content was adjusted to 68 and
118 mg kg
−1 dry soil by adding calcium dihydrogen phosphate in order to study the effects of four rates of phosphate
fertilization on the growth of rice and soil phosphate fertility,
namely: 1) conventional (100 kg ha
−1 ); 2) corresponding to
the exploited amount (40 kg ha
−1 ); 3) corresponding to the
L-type fertilizer (20-10-10) application (20 kg ha
−1 ); and 4)
no phosphate fertilizer added.
The experiment will be conducted for five years and is
now in the second year. The rice yield in the first year was
comparable among the plots and treatments, suggesting that
a reduction of the amount of phosphate fertilizer application
is possible in soils that have phosphate levels equal to or
greater than that of the experimental field in this study, at
least for a single year. However, the soil phosphate fertility
decreased in the treatment with no phosphate fertilizer
application. The sound management of the phosphate fertilizer application should be developed by monitoring the
rice yield and soil phosphate content in the following years
(Table 8.1) (Kudo and Uno, 2012).
(2) Establishment and extension of environmentally
friendly agricultural technologies
In Ishikawa Prefecture, there are several closed water areas
with slow water circulation, and the deterioration of water
quality is regarded as an environmental problem. Kahokugata, the largest lagoon in the prefecture, is a representative
closed water area. The agricultural sector needs to contribute
to the improvement of water quality by reducing the load of
eutrophic substances. In Kahokugata lagoon, there is
reclaimed land where barley, soybean, paddy rice, lotus root,
watermelon, cabbage, and so on are planted, and we are
working on reducing the load of eutrophic substances in
these fields.
So far, for the barley and soybean crops, we have conducted field tests of environmental load-improving cultivation by side-dressing with slow-release fertilizers and have
demonstrated that the total amount of nitrogen discharged
from the field can be reduced by 34% compared with conventional cultivation (Fig. 8.13). In flooded rice cultivation,
we adopted the environmentally-friendly managements of
water and fertilizer: the shallow water-puddling and prevention of forced drainage to suppress discharge of turbid
water, and side-dressing fertilization with slow-release fertilizer. These managements successfully reduced the amount
of discharged total nitrogen and discharged total phosphate
by 23–39% and 34–39%, respectively (Fig. 8.14). We are
now testing the reducing effect of automatic water-saving
irrigation on the load of eutrophic substances in lotus root
cultivation. In the future, we plan to introduce machinery for
local fertilization in vegetable cultivation, which requires
more fertilizers than other crops, and to study the effectiveness of such technology for improving fertilizer utilization and reducing the amount of excess nitrogen loaded into
the lagoon (Uno et al. 2010).
8 Chubu Region (Hokuriku/Tokai)
285