amount of phosphorus fertilizer calculated from the actual
field value of available phosphorus content in soil is estimated to be approximately 62% of the fertilization standards
in Hokkaido. The available nitrogen content in soil has
gradually increased, and in 96% of sites the available silicon
(40 °C; 1 week incubation) is less than the soil diagnosis
criterion.
5.2.2 Fertility Management
(1) Nitrogen
In the case of fertilizer incorporation in the plow layer, the
fertilizing standards of nitrogen in the Hokkaido Fertilizer
Recommendations 2015 (see Sect. 5.8.1) are 65–95 kg ha
−1
in lowland soils, 60–85 kg ha
−1 in terrace soils, and 50–
75 kg ha
−1 in peat soils.
The side-dressing application (applying fertilizer in 3 cm
side line of a hill at a depth of 3–5 cm) has been developed
for accelerating the initial growth due to high nitrogen
concentrations in nearby rice roots. For the side-dressing
method, the rate of nitrogen application is 30–40 kg ha
−1
and the total rate of nitrogen fertilizer application is subtracted by 5 kg ha
−1 from the standard. The side-dressed
nitrogen is mainly absorbed by the plants before the flag leaf
stage and is less distributed in polished rice. Therefore, this
method was effective for producing low-protein rice.
It is recommended to apply about 2 kg ha
−1 of nitrogen
topdressing within seven days of the panicle formation stage,
as this topdressing increases the number of ears and the
number of unhulled rice grains per ear and can increase
resistance to adverse weather conditions. Nitrogen topdressing after the flag leaf stage should be avoided, because
during that time nitrogen is allocated to polished rice at high
rate, which raises the protein content.
(2) Phosphorus
In cold regions, the enrichment of soil phosphorous has been
emphasized, particularly as a countermeasure to cool summer damage, because phosphorous has the effect of accelerating initial plant growth. The fertilizing standard of
phosphorous is determined at 35 kg P ha
−1 (80 kg P 2 O 5
ha
−1 ) in Hokkaido, but it is desirable to increase or decrease
this based on soil diagnosis.
With regard to the method of fertilizer application, we
should put emphasis on using the side-dressing method due
to its effectiveness. It is reasonable that phosphorous
absorption by rice plants depends on the soil condition in the
latter half of the growing period. However, excessive
amounts of fertilizer have been applied in many paddy fields.
It is necessary to improve the phosphorous level in soil,
because the amount of available phosphorous is very high;
the mean value is 218 mg P kg
−1 (500 mg P 2 O 5 kg
−1 ).
(3) Potassium
The fertilizing standard of potassium was set at 66 kg K
ha
−1 (80 kg K 2 O ha
−1 ) in the Hokkaido Fertilizer Recommendations 2015 (see Sect. 5.8.1), based on the degree of
potassium absorption by rice plants. The standard concentration of exchangeable potassium in paddy fields is 125–
249 mg K kg
−1 (150–300 mg K 2 O kg
−1 ). A total of
25 kg K ha
−1 (30 kg K 2 O ha
−1 ) of applied potassium fertilizer should be added to the fertilizing standard if the
amount of exchangeable potassium is 125 mg K kg
−1 or
less, and 25 kg K ha
−1 (30 kg K 2 O ha
−1
) of applied potassium fertilizer should be subtracted from the fertilizing
standard if the amount of exchangeable potassium is
249 mg K kg
−1 or higher.
Potassium is supplied to the soil by the return of rice
straw, as 70% of the potassium in rice plants is distributed in
the stems and leaves. We advise that potassium fertilizer
should be reduced by 33 kg K ha
−1 (40 kg K 2 O ha
−1 ) when
stems and leaves (10 t ha
−1 ) are applied and by 17 kg K
ha
−1 (20 kg K 2 O ha
−1 ) when compost (10 t ha
−1 ) is applied.
(4) Silicon
When we studied rice plant growth in the paddy field for
10 years of successive calcium silicate (slag silicic acid
manure) application, the yield was higher than in a control
field. The rice plants absorbed a lot of silicon, which
improved brown rice production efficiency and decreased the
protein content in polished rice effectively. Accordingly, an
index of available silicic acid of soil was formulated for the
purpose of achieving a protein content of less than 80 g kg
−1
of polished rice. Based on that index, soil with an available
silicon concentration of below 47 mg Si kg
−1 (100 mg
SiO 2 kg
−1 ) is defined as lacking, soil with an available silicon concentration of between 47 and 75 mg Si kg
−1 (100–
160 mg SiO 2 kg
−1 ) is defined as slightly lacking, and soil with
an available silicon concentration of above 75 mg Si kg
−1
(160 mg SiO 2 kg
−1 ) is optimal. Half of paddy fields in Hokkaido require improvement; that is, they are diagnosed as
lacking in available silicon. In particular, principal paddy
field areas (Sorachi and Isikari areas) are low in silicon.
5 Hokkaido Region
141
field value of available phosphorus content in soil is estimated to be approximately 62% of the fertilization standards
in Hokkaido. The available nitrogen content in soil has
gradually increased, and in 96% of sites the available silicon
(40 °C; 1 week incubation) is less than the soil diagnosis
criterion.
5.2.2 Fertility Management
(1) Nitrogen
In the case of fertilizer incorporation in the plow layer, the
fertilizing standards of nitrogen in the Hokkaido Fertilizer
Recommendations 2015 (see Sect. 5.8.1) are 65–95 kg ha
−1
in lowland soils, 60–85 kg ha
−1 in terrace soils, and 50–
75 kg ha
−1 in peat soils.
The side-dressing application (applying fertilizer in 3 cm
side line of a hill at a depth of 3–5 cm) has been developed
for accelerating the initial growth due to high nitrogen
concentrations in nearby rice roots. For the side-dressing
method, the rate of nitrogen application is 30–40 kg ha
−1
and the total rate of nitrogen fertilizer application is subtracted by 5 kg ha
−1 from the standard. The side-dressed
nitrogen is mainly absorbed by the plants before the flag leaf
stage and is less distributed in polished rice. Therefore, this
method was effective for producing low-protein rice.
It is recommended to apply about 2 kg ha
−1 of nitrogen
topdressing within seven days of the panicle formation stage,
as this topdressing increases the number of ears and the
number of unhulled rice grains per ear and can increase
resistance to adverse weather conditions. Nitrogen topdressing after the flag leaf stage should be avoided, because
during that time nitrogen is allocated to polished rice at high
rate, which raises the protein content.
(2) Phosphorus
In cold regions, the enrichment of soil phosphorous has been
emphasized, particularly as a countermeasure to cool summer damage, because phosphorous has the effect of accelerating initial plant growth. The fertilizing standard of
phosphorous is determined at 35 kg P ha
−1 (80 kg P 2 O 5
ha
−1 ) in Hokkaido, but it is desirable to increase or decrease
this based on soil diagnosis.
With regard to the method of fertilizer application, we
should put emphasis on using the side-dressing method due
to its effectiveness. It is reasonable that phosphorous
absorption by rice plants depends on the soil condition in the
latter half of the growing period. However, excessive
amounts of fertilizer have been applied in many paddy fields.
It is necessary to improve the phosphorous level in soil,
because the amount of available phosphorous is very high;
the mean value is 218 mg P kg
−1 (500 mg P 2 O 5 kg
−1 ).
(3) Potassium
The fertilizing standard of potassium was set at 66 kg K
ha
−1 (80 kg K 2 O ha
−1 ) in the Hokkaido Fertilizer Recommendations 2015 (see Sect. 5.8.1), based on the degree of
potassium absorption by rice plants. The standard concentration of exchangeable potassium in paddy fields is 125–
249 mg K kg
−1 (150–300 mg K 2 O kg
−1 ). A total of
25 kg K ha
−1 (30 kg K 2 O ha
−1 ) of applied potassium fertilizer should be added to the fertilizing standard if the
amount of exchangeable potassium is 125 mg K kg
−1 or
less, and 25 kg K ha
−1 (30 kg K 2 O ha
−1
) of applied potassium fertilizer should be subtracted from the fertilizing
standard if the amount of exchangeable potassium is
249 mg K kg
−1 or higher.
Potassium is supplied to the soil by the return of rice
straw, as 70% of the potassium in rice plants is distributed in
the stems and leaves. We advise that potassium fertilizer
should be reduced by 33 kg K ha
−1 (40 kg K 2 O ha
−1 ) when
stems and leaves (10 t ha
−1 ) are applied and by 17 kg K
ha
−1 (20 kg K 2 O ha
−1 ) when compost (10 t ha
−1 ) is applied.
(4) Silicon
When we studied rice plant growth in the paddy field for
10 years of successive calcium silicate (slag silicic acid
manure) application, the yield was higher than in a control
field. The rice plants absorbed a lot of silicon, which
improved brown rice production efficiency and decreased the
protein content in polished rice effectively. Accordingly, an
index of available silicic acid of soil was formulated for the
purpose of achieving a protein content of less than 80 g kg
−1
of polished rice. Based on that index, soil with an available
silicon concentration of below 47 mg Si kg
−1 (100 mg
SiO 2 kg
−1 ) is defined as lacking, soil with an available silicon concentration of between 47 and 75 mg Si kg
−1 (100–
160 mg SiO 2 kg
−1 ) is defined as slightly lacking, and soil with
an available silicon concentration of above 75 mg Si kg
−1
(160 mg SiO 2 kg
−1 ) is optimal. Half of paddy fields in Hokkaido require improvement; that is, they are diagnosed as
lacking in available silicon. In particular, principal paddy
field areas (Sorachi and Isikari areas) are low in silicon.
5 Hokkaido Region
141