Birte Junge, Armin Skowronek:
Physical, Chemical and Biological Degradation of Tropical Soils in a Land Use System with Low Input


University of Bonn, Institute for Soil Science, Germany

IMPETUS (an integrated approach to the efficient management of scarce water resources in West Africa) investigates the effects of global climate change on regional hydrological processes and on water availability in Benin and Morocco since 2000. Within this interdisciplinary project, the current situation of the soils developed in the catchment area of the river Aguima (30 km2, 100 km W of Parakou) and different kind of soil degradation in a land use system with low input were examined.

To determine the influence of agriculture on soils, several investigations were carried out in the pastoral used savanna and on cultivated land during the rainy season of the years 2001 and 2002. Runoff plots were installed on fields with different crops (cotton, yam, maize) and different tillage systems (rows, mounds) and in the savanna for measuring the current soil erosion by water. Additionally, the nutrient supply of crop land in settlements of different ages were compared. To determine the abundance and activity of soil fauna, the population density of earthworms and the production of worm cast were counted and bait-lamina tests as well as litter-bag tests were carried out in different used fields.

The measurements show the most runoff and soil loss on fields with crops planted in rows leading parallel to slope or in mounds. The investigations also indicate a decreasing nutrient supply with increasing time when no fertilizer are used and fallows are shortened. Furthermore, the low population density of earthworms and the reduced production of worm cast also show a biological degradation under the influence of agriculture.

So, land use systems with low input and shortened fallows in Benin lead to different kind of soil degradation which will consequently result in problems for food production in the future.

Keywords: Benin, low input land use system, soil degradation, West Africa


Contact Address: Birte Junge, University of Bonn, Institute for Soil ScienceNussallee 13, D-53115 Bonn, Germany, e-mail:
Andreas Deininger, September 2004