of quartz and three-layer minerals, suggested the presence of a very strong
desilification/ferralitisation process. This seems to be on older surface with the
most dominant process, culminating in a new formation of Gibbsite.
Gibbsite was found not only in the clay fraction but also in the bulk soil, where
the mineral seemed to be clay, because the content in the bulk soil was higher than
in the clay fraction (Schuler 2008; Herrmann et al. 2007). The findings of the profile
analyzed in Vietnam confirm in principle the results found in Thailand; however,
there were two clear exceptions. The first was that in all soils there were found some
three-layer minerals, meaning the soils were not so strongly differentiated and
desilified.
On the other hand, a high share of kaolinite was found, inherited from the rock.
Also, differences were found in the oxides present. Gibbsite was found in all the
samples, but sometimes in minor amounts, and hematite was not found (Table 2.14).
The profiles from Laos were found to sit between those of Thailand and Vietnam.
These lowland profiles all had a dominant share of kaolinite, and also illite, but with
gibbsite almost missing. Some of the goethite may have been transformed into
hematite already. This represents a not so clear differentiation between the soils in
Laos and Vietnam, but is a clear sign that the land surface in Laos is younger. The
overall organic matter content was between 1.5 % and 3 % organic carbon, and the
C/N-ratio was between 10 and 15, decreasing down in the soils to around 5 on
occasion. This reflected an undisturbed but very quick turnover of organic matter.
Table 2.13 Texture and semi-quantitative mineralogical composition of topsoil and subsoil
horizons in the limestone area of Bor Krai in Thailand
a
Soil
Alisol 1759
Acrisol 1780
Ferralsol 1551
Slope (%)
17
35
344
Horizon
Ah
Bt3
Ah1
Bt2
Bo4
Depth (cm)
0–17
56–76
0–20
62–86
150–160
Skeleton (%)
2–5
0–2
0
0
0
Sand (%)
15
13
8
7
3
Silt (%)
44
26
44
13
16
Clay (%)
41
61
48
79
82
Mineralogy
Bulk Clay Bulk Clay Bulk Clay Bulk Clay Bulk Clay
(%)
Gibbsite
0
0
0
0
36
18
37
20
58
45
Kaolinite
21
24
18
24
31
50
36
52
14
22
Illite
13
36
17
38
0
6
0
5
0
0
Intergrade 10–14 A ˚ 0
2 6
0
2 2
0
0
0
0
0
0
Vermiculite
0
5
0
6
3
11
3
10
0
0
Chlorite
0
0
0
0
0
0
0
0
10
11
Quartz
52
0
48
0
11
0
6
0
4
0
Goethite
6
4
9
5
0
0
0
0
0
0
Hematite
8
5
8
5
19
15
18
13
14
22
a
Clay mineral quantification was based on oriented samples without intensity correction taking
place for the different minerals
2 Beyond the Horizons: Challenges and Prospects for Soil Science and Soil. . .
87
desilification/ferralitisation process. This seems to be on older surface with the
most dominant process, culminating in a new formation of Gibbsite.
Gibbsite was found not only in the clay fraction but also in the bulk soil, where
the mineral seemed to be clay, because the content in the bulk soil was higher than
in the clay fraction (Schuler 2008; Herrmann et al. 2007). The findings of the profile
analyzed in Vietnam confirm in principle the results found in Thailand; however,
there were two clear exceptions. The first was that in all soils there were found some
three-layer minerals, meaning the soils were not so strongly differentiated and
desilified.
On the other hand, a high share of kaolinite was found, inherited from the rock.
Also, differences were found in the oxides present. Gibbsite was found in all the
samples, but sometimes in minor amounts, and hematite was not found (Table 2.14).
The profiles from Laos were found to sit between those of Thailand and Vietnam.
These lowland profiles all had a dominant share of kaolinite, and also illite, but with
gibbsite almost missing. Some of the goethite may have been transformed into
hematite already. This represents a not so clear differentiation between the soils in
Laos and Vietnam, but is a clear sign that the land surface in Laos is younger. The
overall organic matter content was between 1.5 % and 3 % organic carbon, and the
C/N-ratio was between 10 and 15, decreasing down in the soils to around 5 on
occasion. This reflected an undisturbed but very quick turnover of organic matter.
Table 2.13 Texture and semi-quantitative mineralogical composition of topsoil and subsoil
horizons in the limestone area of Bor Krai in Thailand
a
Soil
Alisol 1759
Acrisol 1780
Ferralsol 1551
Slope (%)
17
35
344
Horizon
Ah
Bt3
Ah1
Bt2
Bo4
Depth (cm)
0–17
56–76
0–20
62–86
150–160
Skeleton (%)
2–5
0–2
0
0
0
Sand (%)
15
13
8
7
3
Silt (%)
44
26
44
13
16
Clay (%)
41
61
48
79
82
Mineralogy
Bulk Clay Bulk Clay Bulk Clay Bulk Clay Bulk Clay
(%)
Gibbsite
0
0
0
0
36
18
37
20
58
45
Kaolinite
21
24
18
24
31
50
36
52
14
22
Illite
13
36
17
38
0
6
0
5
0
0
Intergrade 10–14 A ˚ 0
2 6
0
2 2
0
0
0
0
0
0
Vermiculite
0
5
0
6
3
11
3
10
0
0
Chlorite
0
0
0
0
0
0
0
0
10
11
Quartz
52
0
48
0
11
0
6
0
4
0
Goethite
6
4
9
5
0
0
0
0
0
0
Hematite
8
5
8
5
19
15
18
13
14
22
a
Clay mineral quantification was based on oriented samples without intensity correction taking
place for the different minerals
2 Beyond the Horizons: Challenges and Prospects for Soil Science and Soil. . .
87