Agriculture Reference
In-Depth Information
which sense? How important is soil classiÝcation? What is the relationship between soil research
and soil classiÝcation?
SOIL CLASSIFICATION
ÑClassiÝcation is a basic requirement of all science and needs to be revised periodically as
knowledge increasesÒ (Isbell, 1996). This is the case for all natural systems. For natural sciences,
classiÝcation Ñserves as a framework for organizing our knowledge of natural systems including
soils and provides a means of communication among scientists, and between scientists and users
of the landÒ (Isbell, 1996).
Unlike other natural systems, soils do not occur as discrete entities but as a continuum over
the landscape. This has led to much controversy regarding what should and can be classiÝed in
terms of soils: Does it make sense to classify individual soil proÝles, or should larger soil bodies,
even soil landscapes (ÑsoilscapesÒ) be classiÝed? Much of this controversy stems from failure
to distinguish between soil classiÝcation
and soil surveying (soil mapping), of which
soil classiÝcation is a component, at different levels of detail. Individual soil proÝles can be
classiÝed perfectly, but proÝles that are very similar can seldom be mapped out separately, and
units such as soil associations need to be used in mapping. Unfortunately, there is a tendency to
see this as something unique to soils, which is not the case. A similar situation is found with
natural vegetation; for example, individual plants can be classiÝed perfectly, but very seldom, if
ever, will a pure stand of a single plant species be found that can be mapped separately. However,
for aspects such as determining the broad vegetation patterns of a country, it is necessary to map
different vegetation units. They also form a continuum over the landscape. These are (like soils)
deÝned and mapped at different levels of detail from biomes (at national level) to plant commu-
nities (at detailed level).
Unlike for plants and animals, a universal soil classiÝcation system does not yet exist that is
used globally in all countries, and a wide array of classiÝcation systems exists. Soil classiÝcation
has historically been linked to agricultural uses of soils. Because dominant soils and agricultural
systems differ widely among different countries, a broad range of systems exists today. As the
demands for soil information are becoming broader and include nonagricultural uses, such as those
concerning environmental issues, soil classiÝcation systems are expected to be modiÝed. There is
an inherent danger in the development of purely technical or utilitarian classiÝcation systems,
because their actual utility is often low, and with new developments they tend to become quickly
obsolete (Kellogg, 1961; Laker, 1978). Laker (1981) listed the following three criteria for a well-
designed soil classiÝcation system (at national level):
senso stricto
1.
It must be comprehensiveÐthat is, it must be capable of accommodating all of the soils found in
the country. Class deÝnitions must be clear, rigorous, mutually exclusive, and based on factual
statements of soil properties.
2.
Only soil properties that are easy to measure and to comprehend should be used as criteria for
higher classiÝcation levels.
3.
ClassiÝcation systems must be well-structured, so that the similarities and differences among soils
can be easily understood.
Several decades ago, Manil (1959) was Ñhoping, however, that in the not too distant future
pedologists would agree on a universal classiÝcation, i.e., universally accepted after discussion
and mutual concessions. It might simply be a system universally accepted as a system of reference
without necessarily being universally applied.Ò In 1998 the IUSS adopted a motion requesting
that all soil scientists adopt the World Reference Base for Soil Resources (WRB), developed
under the auspices of the IUSS, as a reference soil classiÝcation system. In the WRB publication,
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