than the Mn-enriched layer (Wada and Neue 1988; Kyuma 2004), reflecting the
difference in Eh
0 (pH 7) values of the redox reactions related to these elements
(Fig. 5.2).
Poorly drained paddy fields are distributed in marshlands or other areas with high
ground water levels. The lower horizon soil directly under the plow layer is saturated
with water and reduced, even after irrigation is stopped, due to high ground water
level and low water permeability (Fig. 5.5a). The subsoil is bluish gray in color with
faint enrichment of Mn and Fe (Kyuma 2004).
5.2 Hydrated Iron Oxide
Hydrated iron oxides are the most abundant redox-sensitive inorganic constituents in
soil. Here pick up hydrated iron oxide of paddy field soils including iron mottles.
The exemplified iron mottles correspond to redox concentrations described by
Vepraskas (1992) and Hurt et al. (1996). Hydrated iron oxides here may range
from noncrystalline hydrated iron oxide to ferrihydrite and poorly crystalline iron
Fig. 5.5 Poorly drained paddy field soil. (a) Two major types of iron mottles found in paddy field
soils. (b) iron mottles resembling a coating of irregular or vesicular pore surfaces, (c) cylindrical
iron mottles resembling root iron plaque
104
5 Inorganic Soil Constituents Sensitive to Varying Redox Conditions
difference in Eh
0 (pH 7) values of the redox reactions related to these elements
(Fig. 5.2).
Poorly drained paddy fields are distributed in marshlands or other areas with high
ground water levels. The lower horizon soil directly under the plow layer is saturated
with water and reduced, even after irrigation is stopped, due to high ground water
level and low water permeability (Fig. 5.5a). The subsoil is bluish gray in color with
faint enrichment of Mn and Fe (Kyuma 2004).
5.2 Hydrated Iron Oxide
Hydrated iron oxides are the most abundant redox-sensitive inorganic constituents in
soil. Here pick up hydrated iron oxide of paddy field soils including iron mottles.
The exemplified iron mottles correspond to redox concentrations described by
Vepraskas (1992) and Hurt et al. (1996). Hydrated iron oxides here may range
from noncrystalline hydrated iron oxide to ferrihydrite and poorly crystalline iron
Fig. 5.5 Poorly drained paddy field soil. (a) Two major types of iron mottles found in paddy field
soils. (b) iron mottles resembling a coating of irregular or vesicular pore surfaces, (c) cylindrical
iron mottles resembling root iron plaque
104
5 Inorganic Soil Constituents Sensitive to Varying Redox Conditions