Jan-Peter Mund, Thomas Christ:
Sustainable Rehabilitation of Food Crop Production on Inland-Valleys Soils (Marais) in Central Rwanda. Agro-Ecological Conditions and Specific Pedological Determinations

JAN-PETER MUND, THOMAS CHRIST
Johannes Gutenberg University Mainz, Department of Geography, Germany

Since more than thirty years, inland valley soils provide only an extensively used potential for substantial food production in Central Rwanda. In face of an average population density of about 300 inhabitants per km² and more than [90]% agricultural population, nearly the entire Rwandan uplands are already cultivated, primarily for smallholder food production. These agricultural areas are highly endangered by topsoil erosion and the permanent loss of nutrients. The predominantly flat and swampy inland valleys are widely spread landforms east of the Nile-Congo watershed. The mainly unused inland valleys represent the last arable land for the extension of food production especially in the surroundings of the cities.

At the end of the 1970s, the sandy gleysoils of the inland valleys (Marais) started to gain regional importance for cultivation but then fell back into fallow land again. Since 1995, some of them were re-opened and re-habilitated by cooperative food production projects with international support, i.e. the DWHH-Rugeramigozi Project.

The pedological and agro-ecological research was carried out adjacent to Gitarama in the Central Rwandan Uplands and around Butare in Southern Rwanda. All investigated areas are situated in the upper part of the numerous tributaries and sub-catchments which are branched out dendritically of the major river ``Nyabarongo''.

The actual land-use of the valley fringes and the colluvial footslopes is the extensive tillage of manioc or beans whereas the valley bottom remains as swampy Gramineen thicket. In the projet areas the valley bottoms were cultivated with maize, soy and local varieties of beans.

In the valley bottoms stagnic to umbric gleysols are mixed with gleyic arenosols which contain a very low amount of gravel. As a consequence of the hydromorphic conditions characterized by wetness and low soil ventilation, the decomposition rate of plant remnants is low and the humic topsoils possess a high content of organic matter. The major pedological restrictions for agriculture are the sandy valley-bottom soils and the unsteady water supply during the dry season requiring careful irrigation techniques. The high nutrient leaching rates under inadequate production methods may also cause serious problems to the farmers.

Keywords: East Africa, food crop production, inland valley, Marais, Rwanda, valley bottom soils

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Contact Address: Jan-Peter Mund, Johannes Gutenberg University Mainz, Department of Geography, J.- J. Becherweg 21, 55099 Mainz, Germany, e-mail: j-p.mundgeo.uni-mainz.de