ESTIMATION DE L'ÉTAT DE DÉGRADATION DES SOLS SUR MARNES DU PRÉRIF (MAROC) PAR LA SUSCEPTIBILITÉ MAGNÉTIQUE: EXEMPLE DU BASSIN VERSANT DE L'OUED BOUSSOUAB

Abstract

The exploitation of the magnetic susceptibility of soil particles to estimate the state of soil development or its degradation by erosion bases on the comparison of the magnetic susceptibility values and their evolution in depth between stable reference soil and soil which underwent erosion or, on the contrary, receive a contribution of particles. Measures of the magnetic susceptibility of the soil particles on 30 cms deep were made on pedological coverage of one substratum in four zones different by their slope and land use. In the fi rst zone the soil is little evolved. It develops under an exceptionally worked fallow. The average of the magnetic susceptibilities is 7.41 10-8 m3 / kg. In the second zone the ground is developed well on several decimeters. It is extensively exploited by cereal crops. The magnetic average susceptibility is 23.42 10-8 m3 / kg. The third zone is a soil which evolves under a natural herbaceous coverage (alfa) moderately dense. The average of the magnetic susceptibilities of this zone is 13.75 10-8 m3 / kg. The fourth zone completely lost its soil, the substratum is affected itself. The average of the magnetic susceptibilities of this zone is 6.5 10-8 m3 / kg. By comparing the magnetic susceptibilities of these degraded soils and their evolution in depth to those of a stable soil (204.04 10-8 m3/kg) we notice a big difference which allows to estimate the state of their degradation and to determine the factors favoring this degradation. The position of cores on the hillside allowed to have an idea on the particles redistribution by the streaming and consequently on the geodynamics processes of the hillside surface.