regulations for the promotion of environmentally friendly
agriculture in 2003. From the following year, the prefecture
started to subsidize farmers, mostly rice producers, who
fulfilled the requirements for environmentally friendly agriculture, such as limiting the input of chemical fertilizers and
pesticides to less than 50% of the conventional dosages. The
rice produced by this system is certified locally as environmentally conscious rice (“kankyo kodawari mai”). The area
of paddy fields under this system has increased to about 46%
(2017) of the total paddy fields in Shiga Prefecture.
The major agricultural technical development that has
been adopted by such rice producers is classified into two
types: (1) the preservation and reuse of irrigation water by
plastering ridges, puddling with a shallow water depth, and
introducing a circulating irrigation system; and (2) the
minimum input and recycling of fertilizer elements by utilizing polyolefin-coated fertilizer and organic fertilizers such
as cattle manure, green manure, and rice straw, and by
introducing a special rice transplanting machine capable of
applying fertilizer concomitantly.
1. The initial cropping period
Wise water and fertilizer management is the most fundamental and effective strategy for reducing the outflow of N
and P from paddy fields during a cropping period. Management should be conducted with special care during the
initial cropping period, since the inflow of water by irrigation and rainfall into a field during a cropping (irrigation)
period showed a high positive correlation with the outflow of
total N (T-N) and total P (T-P) from the field through surface
water drainage and infiltration (Hasegawa et al. 1992).
Additionally, the outflow of T-N and T-P occurred more
intensively during a period between puddling and 30 days
after transplanting than that during the following cropping
period (Hasegawa 1992).
One of the techniques for wise water management is
puddling and land-leveling with a shallow water depth by
using a paddy field harrow. The paddy field harrow enables
puddling with a shallow water depth at a faster speed than
the conventional rotary harrow, as it has a wider operational
width, shorter tillage blades, and a faster speed of blade
rotation. Furthermore, puddling with a shallow water depth
can decrease the outflow of suspended solids after the puddling, since it causes soil particles to settle faster than in
conventional puddling (Tanaka 2001). This technique also
helps to prevent forced drainage at the time of transplanting.
Another technique for wise fertilizer management is a
localized application of fertilizer to the root zone soil by
using a rice transplanting machine capable of applying fertilizer concomitantly. Because fertilizer can be placed a few
centimeters below the soil surface with this transplanting
machine, the applied chemicals are less susceptible to dissolve in the ponded water and flow out from the field.
When this transplanting technique was combined with
polyolefin-coated urea with a controlled availability, the
yield of rice obtained after the application of 80 kg N ha
−1
was comparable to the yield obtained after the split application of quick-release ammonium fertilizer at 100 kg N
ha
−1 (Table 9.6). This is probably due to the enhanced
recovery of the applied N (Shibahara et al 1992, 2000).
By using the
15 N tracer technique (A value method),
Shibahara (2008) further evaluated the fate of N in different
types of fertilizers (quick-release N, coated N, and
quick-release N plus organic N at 1:1), each of which was
applied uniformly or locally in the root zone. The percentage
of fertilizer-derived N absorbed by rice plants was highest
(49.2%) when coated N was applied locally (Table 9.7). On
the other hand, when organic N was applied together with
quick-release N, the percentage of fertilizer-derived N that
remained in the surface soil after harvest was higher than
40%, and the percentage of the N unrecovered from the
plant–soil system (due probably to denitrification and
leaching) was lower than 20%. These results suggest that the
rate of N application can be reduced most effectively by the
localized application of coated N fertilizer at transplanting
and that the transfer of the applied N from a paddy field to
the surrounding environment can be decreased by the
co-application of organic N with quick-release inorganic N.
2. Rice yield and nutrient flows under the Shiga system
The environmentally friendly rice production in Shiga Prefecture is regarded as an original cropping system and
incorporates a series of the abovementioned technical
developments. The rice producers must reduce the amount of
pesticides and chemical fertilizers to less than 50% of the
conventional dosages, that is, less than seven chemical
components for pesticides and less than 40 kg N ha
−1 for
chemical fertilizers. Moreover, farmers must prevent suspended solids from flowing out of their paddy fields by
decreasing the depth of ponded water during the period
between puddling and transplanting.
We evaluated the effects of this cropping system on rice
yield and nutrient flows at the field scale by comparison with
the conventional cropping system. The results indicated that
the average rice yield over 3 years did not differ significantly
between the two cropping systems (about 5500 kg ha
−1 ),
while the average outflow loads of T-N, T-P, and suspended
solids through surface water drainage could be reduced
significantly under the new cropping system (Table 9.8;
Shibahara 2010).
9 Kinki, Chugoku, and Shikoku Regions
319
agriculture in 2003. From the following year, the prefecture
started to subsidize farmers, mostly rice producers, who
fulfilled the requirements for environmentally friendly agriculture, such as limiting the input of chemical fertilizers and
pesticides to less than 50% of the conventional dosages. The
rice produced by this system is certified locally as environmentally conscious rice (“kankyo kodawari mai”). The area
of paddy fields under this system has increased to about 46%
(2017) of the total paddy fields in Shiga Prefecture.
The major agricultural technical development that has
been adopted by such rice producers is classified into two
types: (1) the preservation and reuse of irrigation water by
plastering ridges, puddling with a shallow water depth, and
introducing a circulating irrigation system; and (2) the
minimum input and recycling of fertilizer elements by utilizing polyolefin-coated fertilizer and organic fertilizers such
as cattle manure, green manure, and rice straw, and by
introducing a special rice transplanting machine capable of
applying fertilizer concomitantly.
1. The initial cropping period
Wise water and fertilizer management is the most fundamental and effective strategy for reducing the outflow of N
and P from paddy fields during a cropping period. Management should be conducted with special care during the
initial cropping period, since the inflow of water by irrigation and rainfall into a field during a cropping (irrigation)
period showed a high positive correlation with the outflow of
total N (T-N) and total P (T-P) from the field through surface
water drainage and infiltration (Hasegawa et al. 1992).
Additionally, the outflow of T-N and T-P occurred more
intensively during a period between puddling and 30 days
after transplanting than that during the following cropping
period (Hasegawa 1992).
One of the techniques for wise water management is
puddling and land-leveling with a shallow water depth by
using a paddy field harrow. The paddy field harrow enables
puddling with a shallow water depth at a faster speed than
the conventional rotary harrow, as it has a wider operational
width, shorter tillage blades, and a faster speed of blade
rotation. Furthermore, puddling with a shallow water depth
can decrease the outflow of suspended solids after the puddling, since it causes soil particles to settle faster than in
conventional puddling (Tanaka 2001). This technique also
helps to prevent forced drainage at the time of transplanting.
Another technique for wise fertilizer management is a
localized application of fertilizer to the root zone soil by
using a rice transplanting machine capable of applying fertilizer concomitantly. Because fertilizer can be placed a few
centimeters below the soil surface with this transplanting
machine, the applied chemicals are less susceptible to dissolve in the ponded water and flow out from the field.
When this transplanting technique was combined with
polyolefin-coated urea with a controlled availability, the
yield of rice obtained after the application of 80 kg N ha
−1
was comparable to the yield obtained after the split application of quick-release ammonium fertilizer at 100 kg N
ha
−1 (Table 9.6). This is probably due to the enhanced
recovery of the applied N (Shibahara et al 1992, 2000).
By using the
15 N tracer technique (A value method),
Shibahara (2008) further evaluated the fate of N in different
types of fertilizers (quick-release N, coated N, and
quick-release N plus organic N at 1:1), each of which was
applied uniformly or locally in the root zone. The percentage
of fertilizer-derived N absorbed by rice plants was highest
(49.2%) when coated N was applied locally (Table 9.7). On
the other hand, when organic N was applied together with
quick-release N, the percentage of fertilizer-derived N that
remained in the surface soil after harvest was higher than
40%, and the percentage of the N unrecovered from the
plant–soil system (due probably to denitrification and
leaching) was lower than 20%. These results suggest that the
rate of N application can be reduced most effectively by the
localized application of coated N fertilizer at transplanting
and that the transfer of the applied N from a paddy field to
the surrounding environment can be decreased by the
co-application of organic N with quick-release inorganic N.
2. Rice yield and nutrient flows under the Shiga system
The environmentally friendly rice production in Shiga Prefecture is regarded as an original cropping system and
incorporates a series of the abovementioned technical
developments. The rice producers must reduce the amount of
pesticides and chemical fertilizers to less than 50% of the
conventional dosages, that is, less than seven chemical
components for pesticides and less than 40 kg N ha
−1 for
chemical fertilizers. Moreover, farmers must prevent suspended solids from flowing out of their paddy fields by
decreasing the depth of ponded water during the period
between puddling and transplanting.
We evaluated the effects of this cropping system on rice
yield and nutrient flows at the field scale by comparison with
the conventional cropping system. The results indicated that
the average rice yield over 3 years did not differ significantly
between the two cropping systems (about 5500 kg ha
−1 ),
while the average outflow loads of T-N, T-P, and suspended
solids through surface water drainage could be reduced
significantly under the new cropping system (Table 9.8;
Shibahara 2010).
9 Kinki, Chugoku, and Shikoku Regions
319