covering 38 %, 34 % and 18 % of the area respectively. The remaining parts were
said to be covered by Orange, Yellow and Mixed soils. The soil quality of the Black
Soils was assessed to be the highest, followed by the Hard Red and Soft Red Soils;
the Orange Soils and the Yellow Soils. Black Soils were characterized as having
high infiltration rates and a high erosion hazard level, and Hard Red Soils as having
low infiltration rates and a medium resistance to erosion. Soft Red Soils were
assigned a low bulk density, a high infiltration rate and a negligible erosion hazard
level, while Orange and Yellow Soils differed solely in terms of color; both were
given low infiltration rates and high levels of erodibility.
High stocks of Nt and S-values were assigned to the Black Soils, and low Nt and
moderate S-value stocks to the Yellow Soils. All other soil types were identified as
having medium-high Nt stocks. Differences in the S-values, in combination with
the mentioned physical soil properties of the remaining local soil types, made
farmers’ differentiations reasonable.
The local soil map and WRB-based soil map appeared to be totally different, while
the local soil map to a large extent corresponded with the petrographic map (Fig. 2.11a).
The WRB map was more or less independent from the parent material and the major
soil types; the major soil types Alisols and Cambisols occurred irrespective of the
parent material and only Acrisols occurred in combination with a specific parent
material, Limestone, at altitudes above 800 m.a.s.l. While the S-value of the major
WRB soil types differed markedly (Table 2.8), a fact which is implicite the soil type
definition, nitrogen stocks were similar and varied a lot within each soil type. This
means that as long as available bases are not a limiting factor, WRB soil classifications
are not suitable for the carrying out of soil quality assessment in this research area.
A poor correlation between WRB-based soil maps and local soil maps has also
been reported by others, notably Payton et al. (2003) and Ali (2003). The main
reasons are seen to be differences in the conceptual bases of the soil-classification
systems used (Niemeijer and Mazzucato 2003). The WRB classification system
considers essential chemical soil parameters (e.g., CEC and base saturation) and/or
properties below the soil surface (e.g., mottles), while local soil types are based on
visible soil color and soil structure, and on tacit knowledge, which is based on
extensive management experience and a holistic perception of a given site.
2.4.5 Cost Aspects of Different Soil Mapping Approaches
Collecting local soil knowledge in north-west Thailand and Vietnam helped to provide
an overview of the main soils in these areas and proved helpful in the appraisal of soil
diversity. It can be concluded that local knowledge is a valuable tool, if one wants to
reduce the number of investigation points, as it helps save time and effort. Based on the
calculated costs of the three soil mapping approaches outlined here (see Table 2.9), the
conventional soil mapping approach used in the Yen Chau research area (17 km
2
)
would cost 34,000 Euros (without laboratory analyses), while the catenary approach
would reduce this cost by two-thirds. Reducing the number of necessary profiles by
2 Beyond the Horizons: Challenges and Prospects for Soil Science and Soil. . .
75
said to be covered by Orange, Yellow and Mixed soils. The soil quality of the Black
Soils was assessed to be the highest, followed by the Hard Red and Soft Red Soils;
the Orange Soils and the Yellow Soils. Black Soils were characterized as having
high infiltration rates and a high erosion hazard level, and Hard Red Soils as having
low infiltration rates and a medium resistance to erosion. Soft Red Soils were
assigned a low bulk density, a high infiltration rate and a negligible erosion hazard
level, while Orange and Yellow Soils differed solely in terms of color; both were
given low infiltration rates and high levels of erodibility.
High stocks of Nt and S-values were assigned to the Black Soils, and low Nt and
moderate S-value stocks to the Yellow Soils. All other soil types were identified as
having medium-high Nt stocks. Differences in the S-values, in combination with
the mentioned physical soil properties of the remaining local soil types, made
farmers’ differentiations reasonable.
The local soil map and WRB-based soil map appeared to be totally different, while
the local soil map to a large extent corresponded with the petrographic map (Fig. 2.11a).
The WRB map was more or less independent from the parent material and the major
soil types; the major soil types Alisols and Cambisols occurred irrespective of the
parent material and only Acrisols occurred in combination with a specific parent
material, Limestone, at altitudes above 800 m.a.s.l. While the S-value of the major
WRB soil types differed markedly (Table 2.8), a fact which is implicite the soil type
definition, nitrogen stocks were similar and varied a lot within each soil type. This
means that as long as available bases are not a limiting factor, WRB soil classifications
are not suitable for the carrying out of soil quality assessment in this research area.
A poor correlation between WRB-based soil maps and local soil maps has also
been reported by others, notably Payton et al. (2003) and Ali (2003). The main
reasons are seen to be differences in the conceptual bases of the soil-classification
systems used (Niemeijer and Mazzucato 2003). The WRB classification system
considers essential chemical soil parameters (e.g., CEC and base saturation) and/or
properties below the soil surface (e.g., mottles), while local soil types are based on
visible soil color and soil structure, and on tacit knowledge, which is based on
extensive management experience and a holistic perception of a given site.
2.4.5 Cost Aspects of Different Soil Mapping Approaches
Collecting local soil knowledge in north-west Thailand and Vietnam helped to provide
an overview of the main soils in these areas and proved helpful in the appraisal of soil
diversity. It can be concluded that local knowledge is a valuable tool, if one wants to
reduce the number of investigation points, as it helps save time and effort. Based on the
calculated costs of the three soil mapping approaches outlined here (see Table 2.9), the
conventional soil mapping approach used in the Yen Chau research area (17 km
2
)
would cost 34,000 Euros (without laboratory analyses), while the catenary approach
would reduce this cost by two-thirds. Reducing the number of necessary profiles by
2 Beyond the Horizons: Challenges and Prospects for Soil Science and Soil. . .
75