Dynamiques salines des sols des milieux arides et semi-arides

Abstract : Bibliometric data about soil salinization suggests that around 1% of soil scientists invest on the subject allthough it concerns a large number of situations where the action of Man is often decisive. The study of the salt dynamics focuses on describing, understanding and predicting solute movement in the soil and the mechanisms that regulate them. Water flows and the ionic liquid phase diffusion are the main salts displacement vectors in and on the soil. The monitoring, the understanding and the prediction of water and solute flows beneficiate from different complementary approaches. First approach based on salt budget considers the soil compartment with two interfaces with the atmosphere and the aquifer. The intervention of regulatory processes can be internal or external to the soil. Agricultural practices for salinity remediation or prevention mobilize these processes. Illustration of the results obtained by salt budget approach is based on the analysis of salt inputs and outputs confirmed by observation and modeling in a rice field soil. During the flooding, field observations seem to reveal a contribution from a artesian salinity flow from the aquifer, while during the drying period the quantification of the evaporation is performed using soil water isotopic species of the molecule of water and chloride ions. Salt budget approach is complemented by the results of surface leaching of salts on the arid soil playas of the Chihuahuan Desert. Salinization may be regulated by feedback effects. For instance field organic matter amendment is one of the traditional methods of struggle against soil salinity shared by many traditions. Our work explains how organic inputs on rice field, allow to control pH, prevent dispersion of clays, with an acceptable methane production increase. Statistical relationships between soil salinity and frequency of surface vegetation organizations were established to illustrate their interactions. Finally, we discuss space organizations induced by salinization or desalination, in the case of plant mosaics or during the extension of salt patches. Prospects are guided by the fact that contamination of surface water and groundwater with pesticides in the Southern Mediterranean countries is very poorly documented, while the intensive irrigated agriculture in these countries is in constant struggle with constraints related to soil salinity induced by poor quality of irrigation and drainage water. The review of the literature shows that in arid situations, it is relatively common to observe positive correlations between the salinity of the water and soil and pesticides contents in surface water or groundwater. Some laboratory studies may identify, molecule by molecule, some explanatory physicochemical processes for these correlations. Nevertheless, insufficient data in Maghreb countries do not allow identifying the mechanisms involved in the environmental situations. Future research will study the mechanisms of the contamination of soil and water by pesticides, highlighting the role of salinity in the irrigated context in North Africa.
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Olivier Grünberger. Dynamiques salines des sols des milieux arides et semi-arides. Sciences de la Terre. Université de Montpellier, 2015. ⟨tel-01140309⟩

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