Agriculture Reference
In-Depth Information
delineated boundaries reÞect the constraints of map scale and the conceptual landscape model of
the surveyor (Hudson, 1992). We do not attempt to map taxonomic concepts. Rather, we use the
taxonomy to classify the soil bodies we have mapped. Concepts such as pedons, polypedons, series,
taxadjuncts, ranges in characteristics, map unit components, similar soils, dissimilar soils, and
multi-taxa map units take signiÝcant effort to be mastered by soil surveyors, and are little understood
outside of our profession. We must always remember that the taxonomy is simply a tool to help
us organize our knowledge and transfer our experience and technology from place to place in the
landscape. Our primary goal is to help individuals and society understand the soil resource by
showing them where the soils are and interpreting, in as simple a manner as possible, their suitability
and limitations for intended uses.
INTRODUCTION
The coupling of Soil Science, Soil ClassiÝcation, and Soil Survey provides a powerful resource
for the beneÝt of humankind. Soil science provides the foundation for our understanding of the
physical, chemical, and biological properties of the soils we depend on to grow crops, sustain
forests and grasslands, and support our homes and societyÔs structures. Soil surveys put our
knowledge into a spatial context so that we know the geographic distribution of the soils. Soil
classiÝcation helps to organize our knowledge, facilitates the transfer of experience and technology
from one place to another, and helps us to compare soil properties. It provides a link between soil
science and soil survey.
A major force driving the development of Soil Taxonomy was the practical need to support the
National Cooperative Soil Survey (NCSS). Dr. Guy Smith wrote
ÑThe system is being developed by the Soil Survey Staff to facilitate the soil survey of the United
States, a cooperative work involving more than fourteen hundred soil scientists working for more than
Ýfty different institutions. Soil maps are being made at a rate of more than sixty million acres each
year. È The classiÝcation, therefore, is being developed to serve a program that has a practical
objectiveÒ (Smith, 1963, p. 6).
The leaders of the NCSS program recognized the need for a classiÝcation system that could
be applied by a cadre of soil scientists with varying education and experience, in a uniform manner.
To do this, they devised a system that used objective criteria that focused on the properties of the
soil itself, rather than on theories of its genesis, as was required by the previous classiÝcation
system (Smith, 1963; Cline, 1963). One of the more ingenious devices of the system is the use of
observable, quantitative diagnostic horizons and features, which reÞect our understanding about
soil genesis. By recognizing these diagnostic horizons and features, and by observing other key
differentiating characteristics, a competent soil scientist is able to objectively observe the soil and
place it into appropriate taxa.
Since 1965, Soil Taxonomy has been a standard recognized by all members of the NCSS. It
has been taught in our universities, and is recognized by many scientiÝc journals as the appropriate
way to communicate about soils in scientiÝc research.
IMPACT OF THE USE OF QUANTITATIVE CRITERIA
The adoption of Soil Taxonomy impacted soil survey operations in a number of ways. These
impacts were primarily the result of the shift from a qualitative to a quantitative emphasis in
observing, describing, and classifying soils (Cline, 1980). Before the adoption of Soil Taxonomy,
the concept of each category in the classiÝcation scheme focused on a central concept, or typifying
