Agriculture Reference
In-Depth Information
the soil scientists. Because of the great geographic extent of soils with plinthite, it was recognized
as a unique soil class in the new Brazilian Soil ClassiÝcation System (EMBRAPA, 1982).
AN OVERVIEW OF THE CURRENT SYSTEM
The current Brazilian Soil ClassiÝcation System, developed and adapted by soil survey staff of
EMBRAPA and its partners, is believed to cover all known soils of the Brazilian Territory. It was
published in 1999 (EMBRAPA, 1999) and presents adaptations of criteria and concepts established
in Soil Taxonomy (Soil Survey Staff, 1975; 1999) as well as in the World Reference Base for Soil
ClassiÝcation (FAO-UNESCO, 1988; FAO/ISRIC/ISSS, 1998). However, the structure of the system
and the emphasis given to criteria differ from these international systems. These differences reÞect
the experience of Brazilian soil scientists, speciÝcally in the context of use and management of the
soils.
The system deÝnes a number of diagnostic characteristics that form the building blocks of the
classiÝcation. As the characteristics have quantitative limits, class deÝnitions are simpliÝed.
Class-deÝning characteristics are incorporated into the key of the hierarchy, and in this manner,
the presence or absence of diagnostic characteristics deÝnes a class. Position in the hierarchy also
ensures that mutually exclusive classes are structured. Subordinate expression of the characteristics
is expressed through the use of intergrades and extragrades, particularly at the subgroup level. By
quantiÝcation and through the use of keys, ambiguity is reduced, enabling all users to arrive at the
same classiÝcation for a soil.
All classiÝcations attempt to partition nature, and there are no perfect systems. The ultimate
test of a system is when multiple users arrive at the same classiÝcation and the same kinds of
interpretations, with respect to use and management. Research and discussions toward a more
perfect system will be focused on better ways to characterize the soils, the rationale for prioritizing
the classes, and the ultimate challenge of meeting the developmental needs of the nation. Differences
in emphasis and variations in the structure between the Brazilian system and other national and
international systems will become evident in this paper. The differences stem from perceptions,
experiences, and the desire to serve the objectives of the classiÝcation system. The intent in this
paper is to elaborate on some of these.
THE BRAZILIAN SOIL CLASSIFICATION SYSTEM
Presently it is structured in six categorical levels, arranged in a hierarchy of increasing infor-
mation content. It comprises 14 classes at Order level, separated by presence or absence of
diagnostic horizons and attributes that reÞect predominant soil-forming processes or mechanisms.
Characteristics or properties that represent important variations within the Order level differentiate
the 44 classes at Suborder level. These characteristics include color, accumulation of organic matter,
complexed organic matter and sesquioxide, degree of salinity, presence of sulfuric horizon, etc.
The 150 classes at Great Group are deÝned on the basis of kind and arrangement of horizons with
depth, exchangeable bases and aluminum saturation, clay activity, presence of sodium or soluble
salts, presence of iron or aluminum oxides, carbonates, etc. Finally, the 580 classes at Subgroup
level comprise the central concept (the typic) and all kinds of intergrades and extragrades soil
classes. Table 11.1 presents the categories and the classes recognized within each category.
Family and Soil Series levels have not yet been developed. They will be deÝned on the basis
of physical, chemical, and mineralogical characteristics that reÞect pedon-environment conditions
that are very important for interpreting soil classes for agriculture and non-agricultural purposes.
Every soil class deÝnition is based on diagnostic soil attributes and properties, according to a
classiÝcation key that reaches to the subgroup level.
