ROOT GROWTH IN REHABILITATED GOLD MINE TAILINGS

Gold mine tailings are characterised by their extreme physical and chemical conditions such as massive clay structure, desiccation cracks, high penetration resistance when dry, low hydraulic conductivity, high pH and salinity. The physical factors affecting root growth in rehabilitated residue materials have not been widely understood and there is a need for further research on the mechanisms of root exploitation in heterogeneous residue layers especially in relation to texture and the development of shrinkage cracks. A trench profile method was used to map the roots of Eucalyptus camaldulnesis and E.gomphocephala along with visible cracks within a residue profile. The maps were digitised and interpreted in ArcView GIS. The basic physical and chemical properties of residue layers were measured both in situ and in the laboratory for 476 soil samples. The results indicate that the roots in tailings exploited the low resistance paths (usually along the cracks) first and then grew laterally along the sandy loam soil layers and bedding surfaces of the residue. Abundant lateral roots were found in sandy loam layers and extended to 25 cm distance away from the nearest cracks. Several residue layers were found to have bulk densities exceeding the threshold values for restriction of root growth estimated from the texture. Root distributions away from cracks were mainly determined by the texture of residue layer and the combination of >18% clay and <30% of sand found to be the main contributing factor to limit root growth in tailings. Penetration resistance, size of the roots and moisture content conformed to linear relationships.