Use of microbiological indicators for evaluating success in soil restoration after revegetation of a mining area under subtropical conditions

Physical (aggregate stability and bulk density) and microbiological (enzyme activities and labile carbon fractions) properties were studied in soils from a degraded mining site and two areas revegetated with Casuarina equisetifolia L. ex J.R. & G. Forst. or Anacardium occidentale L. under subtropical conditions. An adjacent soil under natural vegetation was used as a standard of local, high quality soil. Six years after planting, revegetation with C. equisetifolia or A. occidentale had resulted in higher soil total organic C, water soluble C and carbohydrates, total N content and aggregate stability compared with the bare soil. Soil bulk density decreased sharply after planting of both the tree species, approaching that of soil under native vegetation. Protease-BAA and β-glucosidase activities were higher in the soil revegetated with C. equisetifolia than in that revegetated with A. occidentale, while the remaining activities reached similar values in both the revegetated soils, these being higher than those of the bare soil. It may be concluded that revegetation with C. equisetifolia or A. occidentale rapidly improved soil physical and microbiological properties of a mining area under subtropical conditions. Soil enzyme activities and labile carbon fractions were very sensitive indicators of the improvement in soil quality resulting from the revegetation. Over the duration of this experiment, revegetated soils were still far from reaching the quality levels of the soil under natural vegetation.