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the WRB, and the Þexibility in qualiÝer use lend themselves admirably to describe, characterize, and
classify the fuzzy complexity of natural soilscapes (Duchaufour, 2001). The WRB has opted for
precise deÝnitions of a large number of diagnostic horizons, most of which express one or more
prominent pedogenetic processes. However, when working in the Ýeld, one inevitably comes across
border cases, which triggers the question of whether it is wise to (attempt to) accommodate the worldÔs
highly variable soil resources in a simple categorical system such as the WRB. It appears that for
detailed soil classiÝcation and for the purpose of computerized data management, the WRB ought to
be linked to a more detailed horizon-based system, e.g., the one suggested by Fitzpatrick and Ait-
kenhead (2000). The latter, also called the ÑFitz system,Ò identiÝes soil horizons by properties of the
horizons themselves, in a multidimensional space. The properties are conceived as coordinates, which
intersect in space to create conceptual segments with centroids, or reference points. Each horizon is
uniquely deÝned by its central concept and has a mathematical centroid, which can be used for
quantitative assessment by models or in evaluation schemes. As the Fitz system pursues greater detail
than the broad deÝnitions used in the WRB, there are many horizons (sub-types) for each diagnostic
horizon in the WRB. The Fitz system considers soils to be unique individuals whose identity (border
case or not) can be established by considering the vertical arrangement and thickness of soil horizons.
The Fitz system has adopted the WRB as a reference platform for its own diagnostic horizons.
This presents the WRB with the challenge of harmonizing its diagnostic horizons, properties, and
materials to make the Fitz system and the WRB compatible. Both systems have strengths and
weaknesses, but when used in conjunction they should greatly enhance the usefulness of large soil
databases for quantitative land evaluation.
The FAO stated in its objectives (FAO et al., 1998) that it views the WRB as an easy means of
communication between scientists, to identify, characterize, and name major types of soils. It is
not meant to replace national soil classiÝcation systems, but to be a tool for better correlation
between national systems (Deckers, 2000). National systems are invited to forge a bridge to the
WRB. A logical next step might be to use the WRB as a basic framework and overlay it with the
FAO Topsoil ClassiÝcation. Adding information on soil texture and clay mineralogy may enhance
the system further.
Nachtergaele et al. (2000a) suggest that in the European context, the WRB presents an oppor-
tunity for regional soil services to overcome their differences and adopt the WRB as a common
approach to soil classiÝcation in line with IUSS recommendations. The future success of the WRB
will depend on how compatible the WRB will be with modern information tools and technology,
such as computer databases, Geographic Information Systems, and quantitative land evaluation
procedures. Considering that the WRB is a single-level system (with a second level if one prefers),
regardless of the number of qualiÝers used, the WRB is not hindered by an imposed, strictly
hierarchical structure, which is in line with the requirements of digital information transfer.
REFERENCES
Deckers, J. 2000. Letter to the Editor on World Reference Base for Soil Resources (WRB), IUSS Endorsement,
World-Wide Testing, and Validation.
SSSA J
. 64: 2187.
Driessen, P., Deckers, J., Spaargaren, O., and Nachtergaele, F., Eds. 2001. Lecture Notes on the Major Soils
of the World. World Soil Resources Reports 94, FAO, Rome, Italy.
Duchaufour, P. 2001. Introduction la science du sol. Sol, vgtation, environment. 6e dition de l4 Abrg
de pdologie. Dunot, Paris, ISBN 2 10 005440 6.
Dudal, R. 1996. A World Reference Base for Soil Resources: Background, Principles and Challenges. Pro-
ceedings International WRB Workshop 1996, Pretoria.
FAO. 1974. UNESCO, Soil Map of the World Volume 1, Legend. FAO, Rome, Italy.
FAO/ISRIC/ISSS. 1998. World Reference Base for Soil Resources. World Soil Resources Report #84. FAO,
Rome.
