Page 10 - World Reference Base for Soil Resources of Thailand

Land Development Department Library

5) Qualifiers: related to surface characteristics

6) Qualifiers: related to soil texture and coarse fragment
7) Qualifiers: related to soil colour
8) Qualifiers: related to others properties
2) Supplementary qualifiers
The supplementary qualifiers are not ranked, but are, as a convention,
used in alphabetical order. The supplementary qualifiers are added in brackets after the name
of the RSG and are separated from each other by commas. The sequence is from left to right,
i.e. the first qualifier according to the alphabet is placed closest to the name of the RSG.

3. The rules for classifying soils

3.1 General rules
Classification consists of three steps.

Step one – detecting diagnostic horizons, properties and materials
It is useful to compile a list of the diagnostic horizons, properties and materials
observed. It is possible to make a preliminary classification of the soil in the field, using all
observable or easily measurable properties and features of the soil and associated terrain.
However, the final classification can be made only when analytical data are available.
Step two – allocating the soil to a Reference Soil Group
The described combination of diagnostic horizons, properties and materials is
compared to the WRB Key in order to allocate the soil to the appropriate Reference Soil Group
(RSG). The user should go through the Key systematically, starting at the beginning and excluding

one by one all RSGs for which the specified require.
Step three – allocating the qualifiers
For the second level of the WRB classification, qualifiers are used. The qualifiers
available for use with a particular RSG are listed in the Key, along with the RSG. They are
divided into principal and supplementary qualifiers. The principal qualifiers are ranked and
given in an order of importance. The supplementary qualifiers are not ranked, but are, as a
convention, used in alphabetical order.

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