EDX spectrum of the dashed square in Fig. 4.22d shows that the outside of the
sclerotia grain is Al-rich (Fig. 4.22e)
The largest particle shown in Fig. 4.22a was broken to examine the inside of the
particle, of which the SEM image is shown in Fig. 4.23a. The inside of the particle
displays a reticulated structure. A magnified SEM image (Fig. 4.23b) of the dashed
square in Fig. 4.23a shows that each concavity has a few small holes, which is
characteristic of sclerotia grains (Watanabe et al. 2002). The EDX spectrum obtained
from the whole of Fig. 4.23b shows that the inside of the particle is also Al-rich.
Hence, the Al-rich reticulated structure observed in Fig. 4.21 is the sclerotia grain.
Sclerotia grains contains green pigment compounds related to perylene quinone
(Kumada and Hurst 1967). These green pigment compounds are typically found in
soils containing P-type humic acid. Except the sclerotia grains, a special distribution
pattern for Al is not found in Fig. 4.20a.
The formation of Al-humus, phytoliths, sclerotia grains, and diatoms results from
biological activities in the A horizons. The formation of laminar opaline silica may
be facilitated by the formation of Al-humus. Allophane, imogolite, and ferrihydrite
are formed from inorganic parent materials not only in the A horizons but also in the
Bw horizons of Andisols.
Fig. 4.20 Polished section of A horizon soil. (a) Polished section of a clod obtained from A3
horizon of Fig. 4.19a, (c) magnification of the dashed square (b) of (a), (d and e) Al and Si element
maps of (c), respectively
82
4 Non-crystalline Inorganic Constituents of Soil
sclerotia grain is Al-rich (Fig. 4.22e)
The largest particle shown in Fig. 4.22a was broken to examine the inside of the
particle, of which the SEM image is shown in Fig. 4.23a. The inside of the particle
displays a reticulated structure. A magnified SEM image (Fig. 4.23b) of the dashed
square in Fig. 4.23a shows that each concavity has a few small holes, which is
characteristic of sclerotia grains (Watanabe et al. 2002). The EDX spectrum obtained
from the whole of Fig. 4.23b shows that the inside of the particle is also Al-rich.
Hence, the Al-rich reticulated structure observed in Fig. 4.21 is the sclerotia grain.
Sclerotia grains contains green pigment compounds related to perylene quinone
(Kumada and Hurst 1967). These green pigment compounds are typically found in
soils containing P-type humic acid. Except the sclerotia grains, a special distribution
pattern for Al is not found in Fig. 4.20a.
The formation of Al-humus, phytoliths, sclerotia grains, and diatoms results from
biological activities in the A horizons. The formation of laminar opaline silica may
be facilitated by the formation of Al-humus. Allophane, imogolite, and ferrihydrite
are formed from inorganic parent materials not only in the A horizons but also in the
Bw horizons of Andisols.
Fig. 4.20 Polished section of A horizon soil. (a) Polished section of a clod obtained from A3
horizon of Fig. 4.19a, (c) magnification of the dashed square (b) of (a), (d and e) Al and Si element
maps of (c), respectively
82
4 Non-crystalline Inorganic Constituents of Soil