Soil recovery in a chronosequence of revegetated coal mine spoils in Colombian drylands: a view from the assessment of physical-chemical and biological properties

Characterizing changes in soil properties is essential to understand the effect of land rehabilitation practices and the mechanisms that drive such changes. The objective of this study was to evaluate the recovery of physical-chemical and biological properties of Technosols with increasing rehabilitation age in a chronosequence of dry forests (7, 10, and 21 years) in the El Cerrejón open-pit coal mine (La Guajira, Colombia). Based on previous studies that demonstrated a greater effect of surface change on the physicochemical properties of soils, composite samples taken at two depth levels (0–3 cm and 3–20 cm) were analyzed for each site. The studied properties improved over time, increasing significantly with respect to non-rehabilitated sites, mainly near the surface (0–3 cm). Particularly, after seven years, the increases in soil N content and soil P solution were significant (32% and 71%, respectively). The increased structural and functional development of the vegetation over time led to increased inputs of organic materials via fine litterfall. Overall, soil organic matter (SOM) ranged from 63 to 89% in the rehabilitated sites compared with a reference mature dry forest. Increased SOM is a key indicator of recovery in degraded mine spoils, as it has an outsized ability to influence other soil properties. This represents a positive result for the revegetation/restoration strategy applied at the El Cerrejón mine.