Soil attributes in coal mining areas under recovery with bracatinga (Mimosa scabrella)

The coal reserves in the south of Brazil were intensely exploited at the time of great demand for such fuel. This resulted in changes in the environment, mainly in the chemical, physical and biological characteristics of the soil. Due to the potential to control erosive processes, increase soil quality and restore biological diversity, revegetation is a promising alternative to recover those impacted areas. In that respect, bracatinga is a pioneering tree species that easily grow in different environments and has being planted as vegetation cover in areas under recovery. Therefore, the objective of this work was to characterize the chemical features and to evaluate the soil microbiological attributes in areas degraded by coal mining and under recovery using bracatinga as cover plant. In the bracatinga canopy projection area, soil samples were collected in the environmental restoration areas that have been, at the time of collecting, under a regime of 2, 4, 6 and 12 years of restoration. In addition an area with natural occurrence of bracatinga was used as control. Microbial biomass nitrogen, microbial biomass carbon and microbial biomass respiration increase in average 281, 230 and 157% respectively, when the 12-year-old areas were compared to the 2-year-old-areas. Likewise, a decrease in qCO₂ in the order of 60% was observed for that same comparison. The 12-year-old areas reached the same values of qCO₂ found in the reference area. The data suggest an improvement in the microbiological attributes of the soil with the increase in recovery time for the studied areas. SIGNIFICANCE AND IMPACT OF THE STUDY: In coal mining areas under recovery with typically acid soils, the use of the current recovery strategies (revegetation mainly) has been efficient to increase the quality of soils, especially in the environmental restoration areas. Soil microbiological attributes such as microbial biomass nitrogen, microbial biomass carbon, microbial basal respiration and metabolic quotient (qCO₂ ) are dynamic and highly sensitive. These parameters have the potential to be adopted together with conventional attributes, such as floristic composition indices and species diversity indices, to evaluate the degree of any particular environmental recovery process being conducted at previously explored mining areas.