Agriculture Reference
In-Depth Information
Soilscapes, Soil Sequences: Necessity for a Classification
Numerous works in soil survey have shown the existence of repetitive soil organizations in
many landscapes in France (INRA, 1969Ï2001) and many other countries (Buol et al., 1997). Soil
scientists have often used this concept to deÝne SMUs. The concept of Soilscapes and soil sequences
involves morphological and pedogenetic criteria at the origin of their differentiation. Examples
include scale and spatial arrangement for morphological criteria, factors of differentiation, degree
of relationships, and time for pedogenetic ones. The authors recommend classifying various soil
sequences according to these criteria.
Spatial Scale
Soils constituing a sequence are, geographically, generally quite close. However, this proximity
is relative, and may cover landscape groups of a varied range, simple slope or extensive natural
regions. Scale of investigation here is the most important element to take into account.
Interarrangement of Soils
The taking into consideration of this arrangement as Ñsoil patternsÒ and the functional relation-
ships necessitates a description of the three-dimensional spatial structure of soil types, and if
possible, horizons. Methods of description and expression of the results of these spatial structures
exist (Fridland, 1976; Buol et al., 1997; King et al., 1994; EU-JRC, 1998).
Differentiation Factors
Different genetic factors prove to be
dominant
in the deÝnition of certain Soilscapes or
sequences; if:
¤
The nature of the
is the dominant factor, there is a ÑlithosequenceÒ (gentle slopes
cutting across contrasted stratigraphic units, or variable substrate depth)
parent material
¤
It is a question of
there is a ÑtoposequenceÒ (transfer of dissolved products or particles from
upstream to downstream)
relief,
¤
It is a question of
climate
, there is a ÑclimosequenceÒ (oceanic to continental sequences, or elevation
sequences)
¤
It is a question of the inÞuence of
there is a ÑhydrosequenceÒ (inÞuence of a permanent
water table, distance to the hydrographic collector)
water tables,
¤
It is a question of
there is a ÑchronosequenceÒ (progressive soil differentiation of different
materials, geomorphological origins of relief units such as the succession of terraces)
time,
¤
Human
action is the dominant factor, there is an ÑanthroposequenceÑ (resulting from deforestation,
input or out-take of material, construction of agricultural terraces)
Of course, different qualiÝers may be applied to the same Soilscape. The most frequent
sequences that are closely linked to the dominance of one genetic factor seem to be topographical
and lithological sequences.
Relationships
The functional relationships between soils lead to classifying also the sequences, or catenas
(Sommer and Schlichting, 1997):
¤A catena of ÑtransformationÒ: vertical but no lateral exchange of matter between the soils and
horizons of the sequence
¤A catena of ÑtranslocationÒ: vertical and lateral exchanges of matter between the soils and horizons
of the sequence
