Soil quality assessment of constructed Technosols: Towards the validation of a promising strategy for land reclamation, waste management and the recovery of soil functions.

Mine reclamation has long relied on reusing topsoil to mitigate mining impacts but recently constructed soils (i.e., Technosols) have emerged as novel technologies for restoring post mining landscapes. However, their success depends on their ability to sustain soil functions. To assess the efficiency of a limestone mine reclamation, we measured the soil quality (SQ) of a three- (SC3) and seven-year-old (SC7) Technosol under sugarcane, and one 20-year-old (P20) Technosol under pasture, constructed with limestone spoil in southeastern Brazil. Soil chemical, physical, and biological attributes were evaluated and compared with those of an adjacent natural soil (NS; Rhodic Lixisol). We also tested the Soil Management Assessment Framework (SMAF) for assessing the SQ of the studied soils. SMAF was suitable to detect SQ changes over the years of reclamation. After three and seven years under sugarcane cultivation, the Technosols showed similar SQ indexes (= 0.70 and 0.67) to that of the native soil (SQ = 0.69), whereas after 20 years under pasture the SQ (= 0.88) of P20 was superior to that of NS. Overall, the Technosols recovered most of the ecosystem services expected for healthy soils, especially in P20, where carbon stocks were 2.7 times higher than in NS (82.1 vs 30.35 Mg C ha-1). We highlight the importance of using soil quality assessment tools, such as SMAF, in mine reclamation. In summary, Technosols from limestone wastes could restore basic soil functions under tropical environmental conditions within only 20 years.