Tropentag, October 5 - 7, 2004 in Berlin "Rural Poverty Reduction through Research for Development and Transformation"

Soilscapes of the Drâa Basin / Southern Morocco

University of Bonn, Institute of Soil Science, Germany

Abstract

The Drâa is situated in the dry zone of the southern part of the High Atlas Mountain in southern Morocco. A large N-S-transect (> 400 km) along an extreme gradient of altitude (3.200 - 445 m) and aridity (600 > 50 mm rainfall per year) at 6°30' W longitude is taken. From periglacial up to desert landscapes 13 study sites are chosen. Their soil cover was investigated 2001-2003 to detect differences in their potential use and degradation risk. This was in the framework of the project IMPETUS, - an integrated approach to the efficient management of scarce water resources in West Africa. So-called soil(land)scapes are build up by several polypeda or pedocomplexes and correspond to the pedochore after the choric idea of soil geography (SCHLICHTING 1970). The different soils of a soilscape result in a soil associations. Different soilscapes are presented here using the World Reference Base for Soil Resources (ISSS-ISRC-FAO 1998).
Calcisol-soilscapes on steep slopes and a transmountain basin of the calcareous High Atlas are rich in carbonates (up to 58 %). The silty and loamy silty texture has high contents of gravel (20-86 %). The soil cover of the Leptosol-Regosol-soilscape in the crystalline Anti-Atlas is generally very thin (5-25 cm soil depth) and incompletely conserved between volcanic outcrops. The Leptosol-Regosol-Calcisol-soilscape of the escarpment relief of sedimentary rocks of the middle Drâa is developed with deep Calcisols and their eroded relict as free-rinsed calcrets of a total eroded escarpment. All these soilscapes on slopes indicate a strong degradation by water erosion.
The Arenosol-Fluvisol-Anthrosol-soilscapes of some Drâa oasis include important arable land. These alluvial deposits suffer rising salinisation with the South up to 16,1 dS/m and are no more used there. The occurence of a low ground water table less quality, a finer soil texture and probably more salty alluvial deposits of the southern terrace can explain this situation. The drying former lake Iriqui (end of the Drâa river) is characterised by a Solonchak-soilscape. The Arenosol-Calcisol-soilscape of a neighboured dayet is used as rainfield.

Keywords: Aridity, IMPETUS, soilscape, Southern Morocco

Contact Address: Britta Chafik, University of Bonn, Institute of Soil Science, Bonner Talweg 146, Bonn, Germany, e-mail: b.chafikt-online.de