Agriculture Reference
In-Depth Information
Soils of the Massif Vosgien
In the Vosges, analysis of the soil cover shows two zones of podzolized soils. They are especially
well represented in the zone that corresponds with the presence of the Vosgian sandstones. The
second zone is that of the granitic Vosges; here, the podzolized soils occupy smaller surfaces, and
are limited to the coarsest Ýltering quartz Ñarenites.Ò
The weathered and decayed matter of the granitic rocks is, however, one of the types of material
susceptible, in France, to be affected by podzolization. On the ancient crystalline massifs of the
Vosges and the Massif Central, the podzolization shows up mainly at altitudes above 800 m; the
climatic conditions are therefore cool and humid. The morphology of the proÝles rarely shows a
marked podzolization, but more often than not, expresses a moderate podzolization characterized
by the presence of
podzolic ochric soils
and moderately differentiated
podzols
(
Dystric
or
Spodic
Cambisols
and
Entic
or
Haplic Podzols
[WRB];
Typic
or
Spodic Dystrudepts
[Soil Taxonomy])
.
The products resulting from the alteration of crystalline, volcanic, or metamorphic rocks con-
stitute arenites of varied granulometry according to the quantity and quality of the original weath-
erable minerals and to the intensity of the argilization processes. The migrations-redistributions in
the form of organo-metallic complexes result in the formation, at depth, of spodic horizons. In
addition, this distribution is modulated by the topography; the podzols are situated on the Þats
where the coarse arenites tend to accumulate and where the stability of the materials favors vertical
migrations, as well as the concentration of constituents coming from uphill by lateral migration.
Example from a Medium Mountain Region of the Massif Vosgien
The toposequence shown here comes from a catchment area that is very representative of the
granitic zone of the Massif Vosgien. The parent material is a granite which has been altered to a
granitic arenite with a clayey-sandy texture, but whose weatherable mineral content leads to a
moderate argilization. We therefore have a Soil-system that has differentiated within a lithologically
homogenous material, the pedological evolution being the only process responsible for the soil
distribution. We can observe, from top to bottom of the relief, the different typological units making
up the Soil-system:
Dystric Cambisols, Haplic Podzols,
and
Dystric Fluvisols
(WRB), correspond-
ing to
Typic Dystrudepts, Typic Haplorthods,
and
Typic UdiÞuvents
(Soil Taxonomy).
In Figure 13.4 the preferential location of the podzolization processes on the Þat in the middle
of the slope is clearly shown. The system is arranged from the top toward the bottom of this
relatively steep slope by the succession of STUs (from 1 to 7) and the SMUs (from I to III), which
have been deÝned by medium scale mapping. Two SFUs can be deÝned here; both, however,
generated by the lateral hydric transfers at the level of the structural transition between the granitic
arenite and the underlying rock. The former, situated on the upper part, is at the origin of the
observed podzolisation. The dominant general functioning is therefore constituted by the action of
the lateral Þows mobilizing and displacing certain constituents in the subsoil at the level of the
contact between B horizons and underlaying granite. The Massif Central presents, in its granitic
domain, Soil-systems that are very similar to those that have just been described for the Massif
Vosgien.
Possibilities of Generalizing the Approach
There has always been a problem with generalizing the collected information at a given level
of detail over greater territories. The concepts of Ñdownscaling approachÒ (starting from detailed
maps for smaller scale representations over larger territories), or Ñupscaling approachÒ (going from
general broad-scale knowledge to the choice of representative zones to be inventoried at a more
detailed level), have led to the perfecting of diverse approaches according to environmental con-
ditions.
