levels of chlorite indicate the flood basin of the Yazawa
River and the soils free from chlorite indicate the flood basin
of the Ohoto River.
We measured soil chemical properties of 261 paddy fields
collected by 0.5-km mesh in Tsuruoka City. The spatial
distribution of the soil chemical properties was divided into
three features. The first feature showed lower values of soil
chemical properties in the Akagawa and Ohoyama River
basins and higher values in the Yazawa and Ohoto River
basins. The specific properties and their lower and upper
ranges were as follows: total nitrogen (N), lower range 0.9–
1.9 g kg
−1 , upper range 2.9–5.3 g kg
−1 ; phosphate absorption coefficient (PAC), lower range 3.0–7.5 g P 2 O 5 kg
−1 ,
upper range 12.8–19.5 g P 2 O 5 kg
−1 ; cation exchange
capacity (CEC), lower range 8–14 cmol(+) kg
−1 , upper
range 25–40 cmol(+) kg
−1 ; exchangeable calcium (Ca),
lower range 0.2–1.0 g kg
−1 , upper range 2.0–4.3 g kg
−1 ;
and exchangeable magnesium (Mg), lower range 0.05–
0.19 g kg
−1 , upper range 0.62–1.19 g kg
−1 . Organic matter
in soil forms complexes with clay and becomes stabilized
(Yonebayashi 1997). Additionally, higher ratios of 2:1 clay
mineral in soil lead to the accumulation of higher amounts of
soil organic matter (SOM; Yonebayashi 1997). The soils in
the Yazawa and Ohoto River basins contain relatively higher
levels of smectite than the Akagawa River basin because of
the lower influence of granite from geological features in the
upper reaches of these rivers comparing to the Akagawa
River. Therefore, these soils can accumulate higher amounts
of organic matter, resulting in higher total N, PAC, and CEC
values. Moreover, higher CEC facilitates the absorption of
higher amounts of exchangeable Ca and Mg in these soils.
The second feature showed lower values of soil chemical
properties in the left bank of the Yazawa–Ohoyama River
and higher values in the right bank of the Yazawa–Ohoyama
Fig. 6.1 Spatial distribution of
clay mineral composition in
paddy soils of Tsuruoka city.
A Clay mineral composition free
from chlorite; B Clay mineral
composition slightly contain with
chlorite; C Clay mineral
composition obviously contain
with chlorite. Source
Figure provided by Yuka Sasaki
6 Tohoku Region
187
River and the soils free from chlorite indicate the flood basin
of the Ohoto River.
We measured soil chemical properties of 261 paddy fields
collected by 0.5-km mesh in Tsuruoka City. The spatial
distribution of the soil chemical properties was divided into
three features. The first feature showed lower values of soil
chemical properties in the Akagawa and Ohoyama River
basins and higher values in the Yazawa and Ohoto River
basins. The specific properties and their lower and upper
ranges were as follows: total nitrogen (N), lower range 0.9–
1.9 g kg
−1 , upper range 2.9–5.3 g kg
−1 ; phosphate absorption coefficient (PAC), lower range 3.0–7.5 g P 2 O 5 kg
−1 ,
upper range 12.8–19.5 g P 2 O 5 kg
−1 ; cation exchange
capacity (CEC), lower range 8–14 cmol(+) kg
−1 , upper
range 25–40 cmol(+) kg
−1 ; exchangeable calcium (Ca),
lower range 0.2–1.0 g kg
−1 , upper range 2.0–4.3 g kg
−1 ;
and exchangeable magnesium (Mg), lower range 0.05–
0.19 g kg
−1 , upper range 0.62–1.19 g kg
−1 . Organic matter
in soil forms complexes with clay and becomes stabilized
(Yonebayashi 1997). Additionally, higher ratios of 2:1 clay
mineral in soil lead to the accumulation of higher amounts of
soil organic matter (SOM; Yonebayashi 1997). The soils in
the Yazawa and Ohoto River basins contain relatively higher
levels of smectite than the Akagawa River basin because of
the lower influence of granite from geological features in the
upper reaches of these rivers comparing to the Akagawa
River. Therefore, these soils can accumulate higher amounts
of organic matter, resulting in higher total N, PAC, and CEC
values. Moreover, higher CEC facilitates the absorption of
higher amounts of exchangeable Ca and Mg in these soils.
The second feature showed lower values of soil chemical
properties in the left bank of the Yazawa–Ohoyama River
and higher values in the right bank of the Yazawa–Ohoyama
Fig. 6.1 Spatial distribution of
clay mineral composition in
paddy soils of Tsuruoka city.
A Clay mineral composition free
from chlorite; B Clay mineral
composition slightly contain with
chlorite; C Clay mineral
composition obviously contain
with chlorite. Source
Figure provided by Yuka Sasaki
6 Tohoku Region
187