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1. Definition
| Name |
SOIL
CRUSTING |
| Brief
definition |
Heavy and superficial
layer of soil, almost impermeable. It is a deposit made in
the soil by means of the cementation and precipitation of
some elements dissolved in water, mainly calcium carbonates
or silica. This causes the hardening of superficial formations
in the soil. The calcareous crusting, also known as caliche,
plays a very important part in the landscape modelling in
semi-arid regions, where evapotranspiration ratio are very
high. Soil crust formation, distribution, thickness and hardness
are related to climatic conditions, soluble mineral (carbonates,
silica, iron oxides, etc.) sources, topographic conditions
and relief characteristics.
 |
Crusted
soil, Jumilla, Spain (photo F. López-Bermúdez) |
|
| Unit of measure |
Subjective
classification |
| Spatial scale |
|
| Temporal scale |
|
2. Position
within the logical framework DPSIR
3. Target and
political pertinence
| Objective |
Contribution
to the definition and mapping of ESAs and evaluation of the
desertification risk of an area. |
| Importance
with respect to desertification |
The presence of soil crusting
areas is a very clear indicator of desertification processes
in one area. The formation process (duricrust) has a negative
influence on soil conditions related to porosity and density:
decrease in permeability, infiltration and ventilation; degradation
of structure; limitations for the plants to take root. These
are all aspects linked to the soil organic matter and clay
content, and soil humidity.
Soils that are affected
by crusting, and hence are more liable to suffer water erosion,
are petric calcisol and petric gypsisol. This is because the
presence of a hardened cemented layer which reduces infiltration
and thus increases superficial, or almost superficial, run-off.
Soil crusting is closely
connected to specific climatic conditions, from dry sub-humid
to arid, with the optimum in sub-tropical and semi-arid conditions.
Some types of crusting are specific to Mediterranean areas.
|
| International
Conventions and agreements |
The UNCCD emphasizes
that combating desertification must be tackled within the general
framework of actions to promote sustainable development.
|
| Secondary objectives
of the indicator |
Within the
ESA mode,l objectives include investigation of the individual
processes linked to plant productivity, land degradation and
desertification. |
4. Methodological
description and basic definitions
| Definitions
and basic concepts |
Soil crusting is an expression
used to define soluble materials made by carbonates, silica
and iron oxides that harden and causes soil cementation.
There are more than one
hundred different names for this concept. The process that
creates soil crusting is linked to solution and precipitation
of calcium carbonates in Mediterranean climatic conditions:
The crusting refers the
petrocalcic horizon, as a result of vertical and horizontal
solution movements, precipitation and finally, coming out
to the surface. During the genesis of these soils some oscillations
appear because of change in the climatic conditions such as
times of sediments accumulations, times of precipitation and
times of hardening.
|
| Benchmarks
Indication of the values/ranges of value |
The index can be used
as an indicator of the compacting and crusting risk of the
soil. It is related to the loam, clay and organic matter content,
since these are the elements in soil that have a favourable
effect on its structure.
Lf = % Thin loam
Lg = % Thick loam
C = % Clay
MO = % Organic Matter
|
| Methods
of measurement |
Soil
crusting can be identified in the field, or can be defined by
the using the pedological map of the area, scale 1:25.000 or
less. |
| Limits of the
indicator |
If in the soil
crusting we find different types of geological and pedological
formations then the dominant type is selected for defining ESAs. |
| Linkages with
other indicators |
Soil
depth, Soil texture, Soil
structure, Rock fragments,
Slope gradient, Vegetation
cover, Land
use type. |
5. Evaluation
of data needs and availability
| Data
required to calculate the indicator |
Identification
of the type of soil crusting of the specific area. |
| Data sources |
Necessary data
are usually available and accessible and the cost/benefit ratio
is reasonable. |
| Availability
of data from national and international sources |
Data can be
obtained from various regional, national or international institutions
involved in the collection and the analysis of pedological data. |
6. Institutions
that have participated in developing the indicator
| Main institutions
responsible |
University
of Murcia, Spain |
| Other contributing
organizations |
Universities
of Lisbon, Murcia, Basilicata, Amsterdam, Leeds. Agricultural
University of Athens, Greece |
7. Additional
information
| Bibliography
|
Colloque, 1975: Types
de routes calcaires et leur repartition regionale. Université
L.Pasteur. UER de Géographie.Strasbourg, 146 pp
Dumas,B., 1969 : Glacis
et croûtes calcaires dans le Levant espagnol. Bull.Ass.Géogr.Fr.,
375-376 : 553-561.
Dumas, B., 1978 : Le Levant
espagnol. La génese du relief. Tesis Doctoral. Université
Paris XII, 520 pp.
Goudie, A., 1972 : On
the definition of calcrete deposits. Z.f.Geomorphologie,16,
4: 466
Goudie,A., 1973: Duricrust
in Tropical and Subtropical Landscape. Clarendon Press. Oxford,
177 pp
Laouina, A.,1990 : Le
Maroc Nord-Oriental. Reliefs, Modelés et dynamique
du calcaire. Publications du rectorat de L´Université
Mohammed Ier. Oujda. Maroc., 605 pp.
López Bermúdez,
F., 1981: Geomorfología de las costras calizas. Estudios
Geográficos, 162: 89-103
Rohdenburg, H., Sabelberg,
U., 1969 : Kalkrusten und ihr klimatischer Aussagewert. Neue
Beobachtungen aus Spanien und Nordafrika. Gottinger Bodenkundliche
Berichte: 3-26Rosselló Verger, V., 1973: Costras y
encostramientos calizos en el Sur mediterráneo. Estudios
Geográficos, 131: 423-429
Ruellan, A., 1971: Contribution
a la connaissance des sols des régions méditerranéennes.
Les sols a profil calcaire differencié des plaines
de la Base Moulouya (Maroc Oriental). O.R.S.T.O.M, Paris
Vaudour, J., 1975 : Encroûtements,
croûtes et carapaces calcaires dans la region de Madrid.
Méditerranée, 2 : 39-60
Vaudour,J. ; Clauzon,G.,
1976 : Les coûtes calcaires ont-elles toutes dans une
origine pedologique? Méditerranée,1 : 71-81
Zuidam, R.A. van, 1973
: Calcrete.A review of concepts and an attempt to a new genetic
classification. In Colloque Types de croûtes calcaires,
p. 92
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| Other references |
|
| Contacts
Name and address |
University
of Murcia
Pr. Francisco López-Bermúdez lopber@um.es
Jorge García Gómez jorgegg@um.es |
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