The soil chemical properties of reclaimed land in an arid grassland dump in an opencast mining area in China

Opencast coal mining damages the land in arid grassland mining areas where topsoil is scarce. Restoration of the soil chemical properties is important for land reclamation and the rebuilding of vegetation. We studied a south dump after 4 years of reclamation, a north dump after 8 years of reclamation, and undamaged land to identify changes in the soil profile after mining and reclamation. Variance, correlation, and principal component analyses assessed spatial and temporal differences, and correlations between soil organic matter (SOM), total nitrogen (STN), available phosphorus (SAP), available potassium (SAK), and soil pH (pH) in the 0–40 cm layers. The soil chemical properties were evaluated to support the reconstructed soil profiles and guide soil reconstruction in grassland mining areas. SOM, STN, SAP, and SAK in the south dump were significantly lower than those in the undamaged land. SOM and STN levels in the north dump were lower than those in the undamaged land. SAP and SAK levels in the north dump were higher than those in the undamaged land. Therefore, land reclamation can improve the chemical properties of the reconstructed soil profile in grassland mining areas lacking SAP. Principal component analysis revealed that increasing reclamation years improved the soil chemical quality, and that of the surface soil was better than that of the lower layer. The chemical quality of the soil below 20 cm was consistent. At 0–40 cm, correlations between the soil chemical properties declined from top to bottom, and changed from interdependent to mutually independent; SOM was the core element. The use of topsoil and coal gangue to construct soil profiles can improve the soil chemical properties and resolve the difficulties of land reclamation caused by surface soil scarcity and droughts.