Agriculture Reference
In-Depth Information
problematic. Similarly, soils in China that formed over centuries of sedimentation resulting from
long-term irrigation have morphologies identical to naturally occurring Fluvents that formed on
Þoodplains. Although the physical process of sedimentation is the same, Chinese Soil Taxonomy
separates these soils where anthropogenic activities controlled the processes of sedimentation, and
recognizes the anthropogenic nature of their origin.
Soil Taxonomy (Soil Survey Staff, 1999) and the Brazilian System of Soil ClassiÝcation
(EMBRAPA, 1999) are examples of systems that use morphology-based criteria for deÝning classes,
but processes of soil formation are implied in the construct of the classes. The use of perceived
knowledge of the processes of soil formation is expressly avoided. Neither of these systems
completely incorporates anthropogenic processes, although some horizons and conditions that
developed as a result of anthropogenic processes are recognized. These systems share concepts and
structural characteristics that complicate the incorporation of anthropogenic processes; the problems
associated with incorporating anthropogenic processes are discussed in terms of Soil Taxonomy.
As previously described, anthropogenic soils may or may not contain morphological evidence of
anthropogenic processes. Although soils forming in mine spoil do contain some morphological
features that can be speciÝcally and uniquely related to processes of their origination, those features
are not always present in all polypedons. The same is true of artifacts that may or may not be
present in deeply mixed soils that supported ancient civilizations. As such, these features do not
provide a means of consistently distinguishing these soils from naturally occurring Entisols, Incep-
tisols, or other orders. Additionally, reclamation practices can and do result in reconstructed
morphologies that Ýt the technical description of Mollisols or other soil orders, further complicating
any effort to group anthropogenic soils and separate them from naturally occurring soils with similar
morphology. The heart of the problem lies in the desire to clearly and consistently identify those
soils that formed primarily as a result of anthropogenic processes, although soil morphology does
not always provide clues to these processes. For example, destructive processes, such as excavation
and accelerated erosion, may have profound impacts on pedon and landform morphology, but leave
little or no morphological evidence behind that can be tied conclusively to human activities. Entisols
and many Oxisols and Andisols that have been deeply mixed (>1 m) would still meet the criteria
for inclusion in their respective orders, as would some Histosols and Inceptisols (Soil Survey Staff,
1999), and many soils that have been thoroughly mixed to between 50 and 100 cm deep would
still qualify in the same soil order as their undisturbed analogs. Credibility with users will be lost
if anthropogenic soils are grouped with soils that formed under natural processes because the
morphological evidence to separate them is lacking, especially when the true process of soil
formation is a matter of historical record, the soils contain abundant artifacts, or they occur on
evident anthropogenic landforms.
INCORPORATING CLASSES OF ANTHROPOGENIC SOILS
Additions to Soil Taxonomy have been faced and dealt with many times in the last 25 years,
although there has been a reluctance to add new soil orders. There is a question of whether
anthropogenic soils resemble recent additions. In the 1960s, the authors of Soil Taxonomy were
considering whether to have a separate soil order for soils with aquic conditions, or whether to add
an aquic suborder to each order. The unifying character of these soils was their aquic soil moisture
regime that gives them similarities of behavior and interpretation. They have representatives that
meet the requirements of all other soil orders. They are distributed throughout the world, although
they are more common in level, low-lying areas, and less common in arid areas. It was decided to
add an aquic suborder to each order, rather than classify them as a separate order (Smith, 1986).
The two most recent soil orders that were added to Soil Taxonomy are the Andisols and Gelisols.
It was decided that soils that had andic soil properties (or high potential to develop them) had
unique andic or vitric properties that governed their behavior and management. Soils with andic
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