Agriculture Reference
In-Depth Information
3.
Use interpretations have technical groupings to provide estimates of behavior and responses when
soils are used or managed. The set of properties, their environmental interactions, and expected
changes when managed do not rely on why or how the properties came into being; rather, they
require empirical relationships of properties and their measured behavior.
4.
Equivalency is a means of comparing units or classes in different systems of classiÝcation and
indicating their similarity. Traditionally, it has not itself been a classiÝcation. It has, however, many
similarities regarding deÝnitions and their applications.
With careful attention to details, each system can be adjusted so that it satisÝes its own purpose
and objectives. There will not be a truth discovered, nor will there be a perfect ÝtÐonly a satisfactory
agreement of a purpose and a system. It is absolutely essential that a carefully designed and worded
purpose be stated for a proposed classiÝcation. Without it there can be no testing or evaluation of
the suitability of a system of classiÝcation. A system may be very adequate for its stated purpose,
but not serve other purposes or desires well. It seems that very few soil classiÝcation schemes have
been independently evaluated, although opinions about their usefulness are abundant.
Each purpose implies that soils exist and may be recognized, identiÝed, and their characteristics
used to group or segregate individuals (or components of a continuum). Most scientists agree that
soils have morphology with sets of associated chemical and biological features that uniquely specify
entities that may be treated as individuals of a population of interest.
Soil survey and genetic soil geography require that members of a population be bodies or
segments of landscapes. Many genetic schemes need a small arbitrary volume and associated
features, but do not require geographic attributes to organize them in ways that reveal concepts of
order (especially in nature).
Interpretations do not require genetically determined bodies, or proÝles, and mainly rely on
data sets and their behavior patterns. Why and how a proÝle evolved may be interesting but not
necessary for valid predictions of behavior and response. Correlation tools likely work best with
proÝles or small volumes and data sets for the comparisons that are made to determine membership
in new classes.
What does matter is whether the basic unit is a higher level one, such as a Russian Soil Type
or American Great Group, or a member of the lowest level, such as the Series in Soil Taxonomy.
In the former, extra information is used to subdivide the unit; in the latter, features and properties
are generalized or removed from consideration, as new higher level units and groups are formed
and considered. If soils are individuals as well as bodies, or represent bodies in landscapes, when
are they scale dependent?
The question of soil classiÝcation is less of an issue, because everyone recognizes the improb-
ability of remembering all the kinds of soils, their myriad properties, and their relationships with
each other. Whether dealing with proÝles, pedons, or polypedons, the number is overwhelm-
ingÐthus a multilayered or nested scheme seems appropriate. Kellogg (1936) remarked that soil
classiÝcation helps us to remember the signiÝcant characteristics of soils, to synthesize our knowl-
edge about them, to see the relationships to one another and to their environments, and to develop
predictions of their behavior and responses to management and manipulation. This exempliÝes the
functions or objectives of a classiÝcation.
The sheer numbers commonly dictate a hierarchical system. It can be a word/text document or a
mathematical expression of a multicategorical system with dendrograms and similarity indices or
their equivalent. Each is constructed to abstract characteristics of the population, and to reveal patterns
associated with concepts of order. In addition, there is a need to have inclusive classes that generalize
and group the individuals. This is especially needed when developing generalized maps. It does not
imply, however, that generalized classes provide large areas on generalized maps. It means that large
areas may be named in terms of a few classes. There is a need for an orderly organization of
understanding. Classes at successively higher levels imply segregation of successively more important
qualities, and it is the relationships among the categorical levels that depict concepts of order.
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