5.4 Siderite
Siderite [FeCO 3 ] is sometimes found in the subsoil of poorly drained paddy fields as
white soft or firm nodules. Relatively large siderite nodules were found in a paddy
rice field in Miyagi Prefecture, Japan (Fig. 5.22a). Since the paddy field was used for
soybean cultivation at the time of sampling, the plow layer soil was brown in color.
At depths of 15 cm or deeper, the soil color was bluish gray, indicating reduced
conditions. Siderite was found at a depth of 40–50 cm below the surface (indicated
Fig. 5.22 Siderite in the subsoil of a poorly drained paddy field. (a) Sampling site (arrow shows the
pedon site), (b) soil profile (arrow shows a siderite-rich horizon), (c) close-up of the siderite-rich
horizon (arrow shows an example of a siderite-rich patch), (d) SEM image, (e) element map of Fe,
(f and g) EDX spectra for selected areas (f) and (g) shown in (d), (h) XRD pattern of siderite from
the paddy field subsoil where Q denotes a diffraction peak from quartz, (i) reference XRD data from
Brindley and Brown (1980)
122
5 Inorganic Soil Constituents Sensitive to Varying Redox Conditions
Siderite [FeCO 3 ] is sometimes found in the subsoil of poorly drained paddy fields as
white soft or firm nodules. Relatively large siderite nodules were found in a paddy
rice field in Miyagi Prefecture, Japan (Fig. 5.22a). Since the paddy field was used for
soybean cultivation at the time of sampling, the plow layer soil was brown in color.
At depths of 15 cm or deeper, the soil color was bluish gray, indicating reduced
conditions. Siderite was found at a depth of 40–50 cm below the surface (indicated
Fig. 5.22 Siderite in the subsoil of a poorly drained paddy field. (a) Sampling site (arrow shows the
pedon site), (b) soil profile (arrow shows a siderite-rich horizon), (c) close-up of the siderite-rich
horizon (arrow shows an example of a siderite-rich patch), (d) SEM image, (e) element map of Fe,
(f and g) EDX spectra for selected areas (f) and (g) shown in (d), (h) XRD pattern of siderite from
the paddy field subsoil where Q denotes a diffraction peak from quartz, (i) reference XRD data from
Brindley and Brown (1980)
122
5 Inorganic Soil Constituents Sensitive to Varying Redox Conditions