STUDIES OF THE CAUSES OF SOIL-EROSION ON MARL SOILS IN NORTHERN ALGERIA - THE ROLE OF TRADITIONAL SOIL TILLAGE

In semiarid regions such as the Maghreb, the pressure on natural resou rces such as water and soil are increasing. Reservoir sedimentation an d soil degradation are basic problems in these areas. The Oued Mina wa tershed (5000 km2) has been chosen by the Algerian Ministry of Agricul ture and the Deutsche Gesellschaft fur Technische Zusammenarbeit (GTZ) GmbH for a Technical Cooperation Project to quantify soil erosion and to assess various methods of soil and water conservation at the water shed level. The study area (about 1000 km2) is essentially a landscape of ancient dissected plateaux, with badlands as a major feature in so me places. Both the agricultural areas and the reservoir, located at t he basin outlet, are strongly affected by soil degradation. The climat e is semiarid Mediterranean (wet winters), with an average annual rain fall of 300-350 mm. Investigations using a large rainfall simulator re vealed that soil tillage on marls under semiarid conditions could be a n excellent tool to diminish runoff and soil erosion.