A LOW-INPUT APPROACH TO VEGETATION ESTABLISHMENT ON MINE AND COAL ASHWASTES IN SEMIARID REGIONS .1. TIN MINE TAILINGS IN ZIMBABWE

1. A low input, and hence low cost, approach to the establishment of v egetation on mine and coal ash wastes in semi-arid regions is advocate d and a specific methodology proposed. The aim of such an approach is to accelerate the process of succession leading to the formation of a mature, self-sustaining ecosystem. This approach is illustrated by its application to a tin mine tailings dam in Zimbabwe. 2. Chemical analy sis of the tailings indicated that deficiencies of P, K, Ca, Mg, S and micronutrients, together with aluminate toxicity associated with high pH, might be responsible for the paucity of natural colonization. pho sphorus fixation was shown to be minimal, indicating that low applicat ion rates of P could be used to eliminate this deficiency. 3. Glasshou se and field trials showed the tin waste to be extremely N-deficient. One species of grass (Cynodon dactylon) responded to additions of N, P , K, S, Ca, Mg and micronutrients, whereas an adapted species (Dactylo ctenium giganteum) only responded to N, P and K. 4. Glasshouse species selection trials, with the addition of essential nutrients, showed th at most indigenous plants could grow on the waste, but that herbaceous legumes were more sensitive than grasses or trees. 5. Despite the hot , dry conditions, approximately 40% vegetative cover was established a t the end of the first season, using a moderate rate of compound ferti lizer, and a mixture of adapted trees, grasses and legumes. Selection of rhizobium bacteria under high glasshouse temperatures, using N-defi cient tin waste, was successful in that nodules were observed on site. Evaluation of indigenous tree species on site showed that leguminous species were better able to survive. 6. After one season the low input approach appeared to have been reasonably successful and observations in subsequent years confirm this view.