(Maier 2010; Koch 2010; Sang 2011) for comparing soil quality, soil fertility and
soil suitability assessments. In a sixth village in Chieng Khoi, a local soil map was
also drawn and examples of good, poor and moderate soil qualities (Good Black
Soil, Poor Sandy Soil and Yellow Soil) shown to the assembled group. Soil quality
was assessed by farmers in 10 out of the 15 cases as being low (Table 2.7). Their
quality assessment correlated poorly with stocks of total nitrogen (Nt) and did not
correlate with available bases (S-value). Only Poor Red Soil in Kho Vang and Poor
Sandy Soil in Chieng Khoi were also ranked as poor in respect of Nt, but not in
respect of the S-values, but also soils with high Nt-stocks were evaluated as being
poor. At the local level, in Chieng Khoi the Good Black Soil and Poor Sandy Soil
categories marked the upper and lower limits of soil quality from the farmers’
perspectives, and coincided with nutrient stocks and other fertility parameters
(Fig. 2.19).
In a second trial, the suitability of soils for growing maize was evaluated
according to the FAO/ITC-Ghent method (Sys et al. 1993). This more comprehensive semi-quantitative approach to land evaluation considers soil chemical
properties such as CEC, as well as base saturation, organic matter content and
soil physical properties such as drainage, soil depth, texture and slope. The results
(Table 2.7) showed that most sites were assessed as unsuitable due to the high slope
inclination. Excluding slope inclination, most sites would be considered moderately
suitable (S2), and only one (a Red Yellow Soil in Bad Dan) as very suitable in
accordance with the nutrient stocks.
Nevertheless, the suitability assessments according to the FAO/ITC method
correlated more with the nutrient stocks than with farmers’ assessments, as physical
properties were not a limiting factor. One reason for this might be that single soil
profiles were not representative of local soil unit areas. The variation found in Nt
stocks for seven soil profiles in an area representing a specific local soil type in Ban
Huon village, north-west Vietnam, serves as an example of the heterogeneity of soil
properties found in a local soil unit, with an average of 1.12 Æ 0.82 kg N m
À2 found
in the range 0.26–1.71 kg N m
À2 .
In Vietnam, a local soil map for Chieng Khoi commune was compiled with
experienced farmers from three hamlets during a workshop covering three sessions.
In order to systematically investigate soil variability, 16 representative sites were
chosen covering different slope positions, parent materials and local soil types
along two catenae (1 and 2) and at two additional sites (sites 3 and 4). Based on
local farmers’ knowledge, 12 soil types were identified using a combination of
color (black, red and yellow), textural criteria (sand, gravel and stone content) and
an assessment of soil properties, the erosion hazard level and soil quality with
respect to yield (‘poor’ and ‘good’). The dominant local soil type was identified as a
Black Soils (covering 63 % of the total catchment area) followed by Red Soils
(28 %) and Yellow Soils (9 %). The distribution of soil types was linked to the
relief. Poor Red Soils dominated at the hill top positions and Sandy Black Soils or
Sandy Red Soils were exclusively found at the bottom of the slopes. Soil quality
was understood in terms of yield produced (‘poor’ and ‘good’) and ranked generally
2 Beyond the Horizons: Challenges and Prospects for Soil Science and Soil. . .
71
soil suitability assessments. In a sixth village in Chieng Khoi, a local soil map was
also drawn and examples of good, poor and moderate soil qualities (Good Black
Soil, Poor Sandy Soil and Yellow Soil) shown to the assembled group. Soil quality
was assessed by farmers in 10 out of the 15 cases as being low (Table 2.7). Their
quality assessment correlated poorly with stocks of total nitrogen (Nt) and did not
correlate with available bases (S-value). Only Poor Red Soil in Kho Vang and Poor
Sandy Soil in Chieng Khoi were also ranked as poor in respect of Nt, but not in
respect of the S-values, but also soils with high Nt-stocks were evaluated as being
poor. At the local level, in Chieng Khoi the Good Black Soil and Poor Sandy Soil
categories marked the upper and lower limits of soil quality from the farmers’
perspectives, and coincided with nutrient stocks and other fertility parameters
(Fig. 2.19).
In a second trial, the suitability of soils for growing maize was evaluated
according to the FAO/ITC-Ghent method (Sys et al. 1993). This more comprehensive semi-quantitative approach to land evaluation considers soil chemical
properties such as CEC, as well as base saturation, organic matter content and
soil physical properties such as drainage, soil depth, texture and slope. The results
(Table 2.7) showed that most sites were assessed as unsuitable due to the high slope
inclination. Excluding slope inclination, most sites would be considered moderately
suitable (S2), and only one (a Red Yellow Soil in Bad Dan) as very suitable in
accordance with the nutrient stocks.
Nevertheless, the suitability assessments according to the FAO/ITC method
correlated more with the nutrient stocks than with farmers’ assessments, as physical
properties were not a limiting factor. One reason for this might be that single soil
profiles were not representative of local soil unit areas. The variation found in Nt
stocks for seven soil profiles in an area representing a specific local soil type in Ban
Huon village, north-west Vietnam, serves as an example of the heterogeneity of soil
properties found in a local soil unit, with an average of 1.12 Æ 0.82 kg N m
À2 found
in the range 0.26–1.71 kg N m
À2 .
In Vietnam, a local soil map for Chieng Khoi commune was compiled with
experienced farmers from three hamlets during a workshop covering three sessions.
In order to systematically investigate soil variability, 16 representative sites were
chosen covering different slope positions, parent materials and local soil types
along two catenae (1 and 2) and at two additional sites (sites 3 and 4). Based on
local farmers’ knowledge, 12 soil types were identified using a combination of
color (black, red and yellow), textural criteria (sand, gravel and stone content) and
an assessment of soil properties, the erosion hazard level and soil quality with
respect to yield (‘poor’ and ‘good’). The dominant local soil type was identified as a
Black Soils (covering 63 % of the total catchment area) followed by Red Soils
(28 %) and Yellow Soils (9 %). The distribution of soil types was linked to the
relief. Poor Red Soils dominated at the hill top positions and Sandy Black Soils or
Sandy Red Soils were exclusively found at the bottom of the slopes. Soil quality
was understood in terms of yield produced (‘poor’ and ‘good’) and ranked generally
2 Beyond the Horizons: Challenges and Prospects for Soil Science and Soil. . .
71