Page 8 - World Reference Base for Soil Resources of Thailand

Land Development Department Library

Chapter 1

Background

and basic

1. Basic Principles

1. The classification of soils is based on soil properties defined in terms of diagnostic
horizons, diagnostic properties and diagnostic materials, which to the greatest extent possible

should be measurable and observable in the field.
2. The selection of diagnostic characteristics takes into account their relationship with soil
forming processes. An understanding of soil-forming processes contributes to a better characterization

of soils but these processes should not, as such, be used as differentiating criteria.
3. To the extent possible at a high level of generalization, diagnostic features that are

of significance for soil management are selected.
4. Climate parameters are not applied in the classification of soils. It is understood that
they should be used for interpretation purposes, in combination with soil properties, but they

should not form part of soil definitions. The classification of soils is therefore not subordinated
to the availability of climate data. The name of a certain soil will not become obsolete due to

global or local climate change.
5. The WRB is a comprehensive classification system that enables accommodation of
national soil classification systems.

6. The WRB is not intended to be a substitute for national soil classification systems,
but rather to serve as a common denominator for communication at the international level.
7. The WRB comprises two levels of categorical detail:

 the First Level having 32 Reference Soil Groups (RSGs);
 the Second Level, consisting of the name of the RSG combined with a set of
principal and supplementary qualifiers

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