A low input approach to vegetation establishment on mine and coal ash wastes in semi-arid regions. I. Tin mine tailings in Zimbabwe.
A low input, and hence low cost, approach to the establishment of vegetation on mine and coal ash wastes in semiarid regions is advocated 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. Chemical analysis of the tailings indicated that deficiencies of P, K, Ca, Mg, S and trace elements, together with aluminate toxicity associated with high pH, might be responsible for the paucity of natural colonization. Phosphorus fixation was shown to be minimal, indicating that low application rates of P could be used to eliminate this deficiency. Glasshouse 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 trace elements, whereas an adapted species (Dactyloctenium giganteum) only responded to N, P and K. Glasshouse species selection trials, with the addition of essential nutrients, showed that most indigenous plants could grow on the waste, but that herbaceous legumes were more sensitive than grasses or trees. Despite the hot, dry conditions, approximately 40% vegetative cover was established at the end of the first season, using a moderate rate of compound fertilizer and a mixture of adapted trees, grasses and legumes. Selection of Rhizobium bacteria under high glasshouse temperatures, using N-deficient 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. After one season the low input approach appeared to have been reasonably successful and preliminary observations for a further 18 months supported this view.