Agriculture Reference
In-Depth Information
superposition of soliÞucted material, apparently dating from the late glacial period and by collu-
viated materials, the uppermost of which are contemporary with present-day phenomena.
The typological units comprising this landscape are, from top to bottom of the hill slope,
Eutric
Luvisols, Rendzic Leptosols, Haplic Calcisols,
and
Eutric Fluvisols
(WRB), corresponding succes-
sively to
Typic Hapludalfs, Lithic Haplrendolls, Rendollic Eutrudepts,
and
Typic UdiÞuvents
(Soil
Taxonomy).
Figure 13.2 shows the arrangement of this system, comprising the STUs distributed on the
slopes of the catchment area (from 1 to 6). The SMUs that could be distinguished using detailed
mapping (from I to III), as well as the SFU characterizing the dynamics of this Soil-system, are
also included. The dominant functioning is represented here by the phenomenon of degradation of
surface layers by rain (structure breakdown and crusting/surface sealing), resulting in intense runoff
and water erosion processes. The system described also corresponds with numerous landscapes of
southwest France, where loamy material covers marly calcareous formations.
Soils on the Detritic Formations of the Centre Region
Large areas of the central region are covered by old weathering products of the French Massif
Central. Therefore soils of the region have different origins consisting mainly of ancient detritus
of the Sologne, which is frequently resting on clay sediments, and Þuviatile deposits, which are
linked to the hydrologic network of the Loire, and are located on terraces and along riverbanks.
These formations may present varied granulometric distributions; in other words, the riverbanks
show a dominance of the sandy fraction, while a large part of the recent alluvial deposits are richer
in silty fractions.
Soil differentiation is extremely complex, and in it we can observe numerous transitions between
the well-known evolutionary types, with the frequent intervention of a clay substrate at shallow or
medium depth, creating occasionally predominant hydromorphic conditions. The Soil-systems of
the type
planosols/hydromorphic soils
(
Planosols/Gleysols
[WRB]
; Aquic
or
Albaquic Haplu-
dalfs/Aquepts
[Soil Taxonomy]) or
hydromorphic soils/podzolic soils
(
Gleysols/Spodic Gleysols
or
Entic Podzols
[WRB]);
Aqualfs
or
Aquepts/Entic Haplorthods
[Soil Taxonomy]) typify numerous
landscape units. Leaching may be followed by a moderate podzolization.
Example from a Depressed Area on a Detritic Cover in the Central Region
This example typiÝes numerous Soilscapes of the detritic zones, located in the foothills of the
mountainous and hilly massifs. They extend furthest to the approaches of the hydrologic network
that drains the northern slopes of the Massif Central. These sediments constitute the accumulation
of alteration products resulting from the geomorphological phenomena representative of different
geological periods. The detritic materials are comprised of a sedimentary superposition of clayey
sands and compact clay formations. The two main typological units present and generating this
soil system are, from the interÞuve to the depression,
Dystric Planosols
giving way to
Umbric
Gleysols
(WRB), that is to say
Albaquic Hapludalfs,
which pass into
Typic Humaquepts
(Soil
Taxonomy).
Figure
13.3 shows the arrangement of the system, which is composed of the STUs following
one another on a very gentle slope (from 1 to 5). The SMUs shown by a detailed mapping (from
I to III), as well as the SFU linked to the dominance of the hydric Þows in this system, are also
illustrated. The dominant functioning is represented by the mainly lateral orientation of the hydric
transfers at the level of the particularly prominent planic contact. The system described here is also
found very often in the northern foothill zones of the Massif Central.
