Tropentag, October 5 - 7, 2011 in Bonn "Development on the margin"

Degraded Land Rehabilitation of Coltan Mining Sites in Western Rwanda with Local Organic Materials

¹University of Kassel, Organic Plant Production and Agroecosystems Research in the Tropics and Subtropics, Germany
²National University of Rwanda, Department of Crop Production and Horticulture, Rwanda

Abstract

Little is known about the effectiveness of low-input methods to rehabilitate wastelands from coltan (tantalum) mining in Africa. This study therefore investigated a combination of organic soil amendments to promote the growth of leguminous agro-forestry species on degraded soils of the Gatumba region of Western Rwanda. Three fast-growing leguminous species, Tephrosia vogelii Hook., Leucaena diversifolia (Schlecht) Bentham and Cajanus cajan (L.) Millsp. were grown over four months on three substrate types collected from the local mining sites: a pegmatite dump (S1), a technosol (S2), and a pegmatite dump developing into a gleysol (S3). These substrates were amended 1:1 (w/w) with (i) compost (kitchen refuse plus garden waste, S1/S2/S3+CP), (ii) manure (cattle faeces plus bedding and urine, S1/S2/S3+M) and the equal part combination of compost plus manure (S1/S2/S3+(CP+M)). Manure and compost were applied at 5 t dry matter (DM ha^-1). For all species, the growth parameters including survival rates (2 months after sowing; MAS), plant height (4 MAS), shoot dry matter (4 MAS) and root dry matter (RDM; 4 MAS) were determined. Survival rate of T vogelii was highest compared to the other species and varied from 39% (S1+M) to 56% (S1+CP+M); 50% (S2+M and S2+CP; respectively) to 61% (S2) and from 28% (S3+CP) to 67% (S3). Irrespective of soil types and species, substrate amended treatments yielded higher plants than unamended controls. C. cajan plants were highest averaging 54.4 cm for S1+CP+M, 60.2 cm for S2+CP+M, and 47.9 cm for S3+M. Although heights of T. vogelii were smallest regardless of substrate, its shoot dry matter (29.3 g plant^-1) and root dry matter (0.9 g plant^-1) was highest on S2 due to the combined effects of CP+M. On S3 manure application promoted the shoot development of all species, but most for T. vogelii (21.6 g plant^-1) corresponding to a 91% increase compared to the unamended control. Of the species tested T. vogelii seems most suitable for the recultivation of degraded mining soils given its high survival rate. Its development can be substantially enhanced by the application of compost or compost+manure.

Keywords: Agro-forestry species, coltan mine reclamation, compost, manure shoot and root biomass, survival rate

Contact Address: Rodrigue V. Cao Diogo, University of Kassel, Organic Plant Production and Agroecosystems Research in the Tropics and Subtropics, Steinstraße 19, 37213 Witzenhausen, Germany, e-mail: diogouni-kassel.de