R.W. PLENDERLEITH and L.C. BELL

Department of Agriculture, University of Queensland, Brisbane, Australia.

Abstract

Twelve grasses were screened in a glasshouse trial to evaluate their suitability for the revegetation of mining wastes containing abnormally high concentrations of plant-available Cu. Rhodes grass, buffel grass, green panic, green couch, Makarikari grass, signal grass, setaria, Sabi grass, Indian couch, pearl millet, black speargrass and African lovegrass were grown in a fertilised alluvial soil to which Cu had been added at rates of 2 to 600 mg/kg Cu. Plant top yield, tissue Cu concentrations and soil Cu extracted by 0.02 and 0.1 M EDTA, 0.005 and 0.05 M DTPA, 0.01 M CaCl₂ and deionised water were measured.
The Cu tolerance of the grasses, assessed by added or extractable Cu at 50% yield reduction, decreased in the order: pearl millet > Sabi grass = Rhodes grass > Indian couch > buffel grass > green couch = setaria = African lovegrass = signal grass = green panic = Makarikari grass > black speargrass.
Although "critical" Cu concentrations for toxicity in plant tops could not be assessed for individual species, an analysis of the data for the combined species gave a critical toxic concentration of 18 mg/kg.
The extracts, 0.005 M DPTA and 0.02 M EDTA, were the most convenient for routine analyses of soils. For each of the soil extractants tested, extractable Cu values corresponding to 90% and 50% relative yield are cited for the least and most tolerant grass species.