with soils under arable land. In Chieng Khoi, where soil under forest unaffected by
erosion and suitable reference sites could not be found, soils different in terms of
their relief position, parent materials, duration of cultivation and level of erosion
hazard were compared.
2.6.1 Materials and Methods
The climate in Yen Chau district is described in Chap. 3 of this book. The geology
of the area is characterized by a rift structure, and two major geological units were
distinguished during the study: (1) lower altitude, Upper Cretaceous red colored
clastic sediments (sandstone, claystone and siltstone) with inter-bedding of calcareous conglomerate – all members of the Yen Chau Formation, (2) higher altitude
Middle-Triassic limestone, (3) Late-Triassic clayey shale (Bao 2004; Nguyen
2005), and to a lesser extent (4) calcareous clastic sediments (marl).
Study sites. Chieng Koi, located at between 410 and 550 m.a.s.l., was chosen to
be representative of the geological unit clastic sediments, while Muong Lum,
located between 800 and 900 m.a.s.l., was chosen for its limestone and clayey
shales. Any investigation carried out into the impact of erosion on soil fertility
requires soil profiles to be assessed at both eroded and non-eroded sites. In Yen
Chau district, largely undisturbed sites under forest were found on limestone (three
sites), clayey shale (two sites) and marl (one site). These reference sites were then
compared with cultivated sites over different time spans. In addition to the study
sites in Chieng Khoi on clastic sediments and in Muong Lum on limestone and
clayey shale (CK-S, ML-L and ML-C), three sites in two other villages were
selected, these being Na Khoang, located at the foot slopes of a Triassic limestone
ridge set at 500 m.a.s.l. – with soil derived from marl (NK-M), and also Ban Dan,
located between 800 and 900 m.a.s.l. and comprised of soils derived from limestone
and clayey shale (BD-L, BD-C). The reference profiles were situated under semi
deciduous tropical monsoon forest and had never been used for cultivation
purposes. Muong Lum, a site under secondary forest which had first been slashed
32 years before and used for agriculture for only 3 years before being left fallow,
was used as a reference site. All the study sites were situated at steep inclinations
(around 24–48 %), and in mostly straight or slightly convex middle or upper slope
positions. In Chieng Khoi, no undisturbed soil could be found; instead, soil profiles
representing different relief positions, facies of parent material, cultivation
durations and levels of erosion hazard were compared. The profiles of two catenas
(catena 1 and 2) and an additional site (site 4) were described and analyzed
(Clemens et al. 2010). The soils for catena 1 and site 4 were presumed to be derived
from siltstone, and the soils of catena 2 from sandstone. Site 4 was chosen because
it had been deforested only 7 years previously, while all the other sites had been
used for 23–30 years by the time of the study. Information about the relief positions,
inclinations, slope forms and land use histories of the study sites is given in
Table 2.15.
2 Beyond the Horizons: Challenges and Prospects for Soil Science and Soil. . .
91
erosion and suitable reference sites could not be found, soils different in terms of
their relief position, parent materials, duration of cultivation and level of erosion
hazard were compared.
2.6.1 Materials and Methods
The climate in Yen Chau district is described in Chap. 3 of this book. The geology
of the area is characterized by a rift structure, and two major geological units were
distinguished during the study: (1) lower altitude, Upper Cretaceous red colored
clastic sediments (sandstone, claystone and siltstone) with inter-bedding of calcareous conglomerate – all members of the Yen Chau Formation, (2) higher altitude
Middle-Triassic limestone, (3) Late-Triassic clayey shale (Bao 2004; Nguyen
2005), and to a lesser extent (4) calcareous clastic sediments (marl).
Study sites. Chieng Koi, located at between 410 and 550 m.a.s.l., was chosen to
be representative of the geological unit clastic sediments, while Muong Lum,
located between 800 and 900 m.a.s.l., was chosen for its limestone and clayey
shales. Any investigation carried out into the impact of erosion on soil fertility
requires soil profiles to be assessed at both eroded and non-eroded sites. In Yen
Chau district, largely undisturbed sites under forest were found on limestone (three
sites), clayey shale (two sites) and marl (one site). These reference sites were then
compared with cultivated sites over different time spans. In addition to the study
sites in Chieng Khoi on clastic sediments and in Muong Lum on limestone and
clayey shale (CK-S, ML-L and ML-C), three sites in two other villages were
selected, these being Na Khoang, located at the foot slopes of a Triassic limestone
ridge set at 500 m.a.s.l. – with soil derived from marl (NK-M), and also Ban Dan,
located between 800 and 900 m.a.s.l. and comprised of soils derived from limestone
and clayey shale (BD-L, BD-C). The reference profiles were situated under semi
deciduous tropical monsoon forest and had never been used for cultivation
purposes. Muong Lum, a site under secondary forest which had first been slashed
32 years before and used for agriculture for only 3 years before being left fallow,
was used as a reference site. All the study sites were situated at steep inclinations
(around 24–48 %), and in mostly straight or slightly convex middle or upper slope
positions. In Chieng Khoi, no undisturbed soil could be found; instead, soil profiles
representing different relief positions, facies of parent material, cultivation
durations and levels of erosion hazard were compared. The profiles of two catenas
(catena 1 and 2) and an additional site (site 4) were described and analyzed
(Clemens et al. 2010). The soils for catena 1 and site 4 were presumed to be derived
from siltstone, and the soils of catena 2 from sandstone. Site 4 was chosen because
it had been deforested only 7 years previously, while all the other sites had been
used for 23–30 years by the time of the study. Information about the relief positions,
inclinations, slope forms and land use histories of the study sites is given in
Table 2.15.
2 Beyond the Horizons: Challenges and Prospects for Soil Science and Soil. . .
91