Agriculture Reference
In-Depth Information
lessons will be useful when further reÝnements are attempted. They will also be useful to others
when they embark on a similar exercise, and to some countries that are developing national systems.
INTRODUCTION
ÑScience is a process of discovery, not conÝrmation. Let us allow for the occasional, delicious surprise
that makes us rethink all we thought we knew.Ò
P. Shipman
With the publication of the second edition of Soil Taxonomy (Soil Survey Staff, 1999), a new
era in the development of the system was put in place. In the 25 years since the Ýrst edition (Soil
Survey Staff, 1975), signiÝcant changes in our understanding of soils have taken place as a result
of systematic investigations accompanying the progress in soil survey. The progress has been
worldwide, with developments in other classiÝcation systems and with the contributions of many
foreign scientists to Soil Taxonomy. Many countries are in the process of or contemplating revisions
of their respective systems. A notable event is the publication of the World Reference Base for soil
classiÝcation (Deckers et al., 1998), an effort by the International Union of Soil Science supported
by the Food and Agriculture Organization of the United Nations.
Historical developments leading to the publication of the Ýrst edition of Soil Taxonomy (Soil
Survey Staff, 1975) were reviewed by Smith (1983). Changes in the second edition (Soil Survey
Staff, 1999) have been mainly in the addition of new classes at different categoric levels, requiring
reorganization of the categories and deÝnitions. The Orders of Andisols and Gelisols were intro-
duced, and Aridisols and Oxisols were signiÝcantly modiÝed. Appropriate changes in the lower
categoric levels were made with new deÝnitions or new classes. The basic structure of the system
has not changed since its 1975 debut (Soil Survey Staff, 1975). The basic principles that guided
the development of the system have been explained in several publications (Arnold, 1990; Arnold
et al., 1997; Cline, 1949, 1963, 1971; Simonson, 1963; Smith, 1963; Witty and Eswaran, 1990).
Most of the accepted notions of Soil Taxonomy and its relationship to soil genesis were brought
together in two volumes of a topic edited by Wilding, Smeck, and Hall (1983).
Despite the voluminous amount of information on Soil Taxonomy, students of the system
and knowledgeable users still have questions that are not adequately addressed or elaborated on.
Guy Smith, the prime coordinator for development of the system, provided answers for some of
the major decisions made in designing the system, and Forbes (1986) summarized these. However,
Guy Smith stated at the outset of his interviews, ÑI rather concealed the reason for doing this
when I wrote Soil Taxonomy. If I had explained why we did this or that, the reader would be
more apt to pay attention to the reason than to the actual deÝnition. We wanted a test of the
deÝnition, not of the reason.Ò The reasoning for the structure of the system would perhaps remain
speculative. Some of the rationale, however, was explained later by Guy Smith and others for
various reasons: (a) to better appreciate the system, (b) to compare it with other systems to test
for potential weaknesses in Soil Taxonomy, and (c) to use it as an exercise for developing an
ideal classiÝcation system.
The purpose of this paper is to evaluate Soil Taxonomy in a retrospective manner, and to
enunciate some principles related to the architecture of the system. Such an analysis could
help others develop national systems, or at least suggest areas for their consideration. We have
organized the paper around questions that lead us to concepts that are the foundation of soil
classiÝcation throughout the world. The questions are these: Why soils? What is soil? Why
classiÝcation? and What objectives? These points are followed by consideration of the conse-
quences of the answers to these questions. We conclude with some ideas on minimizing
prejudice for the future.
