Agriculture Reference
In-Depth Information
most limiting characteristic only at the subgroup level; (5) the ambiguity of ÑPaleÒ great groups,
which include soils with thick argillic horizons and soils in which the subsoil high clay content is
inherited from the parent material; (6) the dilemma of paddy soils, whose classiÝcation fails to
capture the particular conditions of these soils; and (7) the predicament of the kandic horizon,
whose introduction may not have been warranted. We examine these issues in some depth, and
present possible solutions.
INTRODUCTION
Documenting the soil resources of the world is a formidable task, and modern classiÝcation
systems have made great strides toward this goal. In the United States, efforts to build a modern
classiÝcation commenced in the early 1950s, and an operational system called the 7
Approximation
(Soil Survey Staff, 1960) became available in 1960. Major revisions since then led to the Ýrst
edition of Soil Taxonomy (Soil Survey Staff, 1975), and eventually the second edition in 1999 (Soil
Survey Staff, 1999). Between the 1975 and 1999 editions, major revisions were made, and many
of the changes were directed at classifying the soils of the tropics. This was made possible through
a project (Soil Management Support ServicesÏSMSS) funded by the U.S. Agency for International
Development (Eswaran et al., 1987) under which benchmark soils in the tropical regions were
sampled, and studies and international committees were initiated to help reÝne Soil Taxonomy.
SMSS established a process and protocol for evaluating, testing, and validating proposals to change
Soil Taxonomy emanating from outside the U.S. With the termination of SMSS in 1994, this process
was no longer operational, and the information delivery and feedback mechanism from international
sources declined.
The focus during the SMSS program was on major issues articulated by international experts.
However, there are many other issues embedded in Soil Taxonomy that affect the classiÝcation of
soils of the tropics, which were not considered, and there still remain problem areas waiting for
resolution. In the interim period between 1975 and 1999, SMSS and later the Natural Resources
Conservation Service (NRCS) issued a biannual publication called ÑKeys to Soil TaxonomyÒ that
incorporated all accepted changes and modiÝcations to the system. The Keys served a very important
function by permitting persons to Ýeld-test the changes, thereby validating the system. With the
termination of the SMSS process, validation from outside the U.S. has become an
th
activity.
The consequences of this are observed in some of the changes recently introduced in Soil Taxonomy.
It should be pointed out at the outset that the issues presented in this chapter do not detract from
the excellent quality of Soil Taxonomy, and that Soil Taxonomy still remains the most advanced
soil classiÝcation in the world.
Having been intimately involved with and having contributed to the process of enhancing Soil
Taxonomy, the authors of are keenly aware of the difÝculties of obtaining a consensus, even on
scientiÝc concepts. Thus in identifying the issues and suggesting solutions, we have attempted to
make them in the context of the guiding principles and concepts of the system (see Arnold and
Eswaran, this publication). We are also cognizant of the fact that the classiÝcation of natural systems
must necessarily be, to some extent, arbitrary and qualitative, and that subdividing a natural
continuum is always artiÝcial. Hallberg (1984) states that Ñthe best of classiÝcation schemes, at
any given time, are merely an index of the evolution of our knowledge. Such schemes must be
tested, and must be capable of growth and change as our knowledge changes.Ò It is in the spirit of
the last statement that we attempt to evaluate the classiÝcation of soils of the tropics according to
Soil Taxonomy.
ad hoc
