Selection of topsoil alternatives from overburden of surface coal mines

Abstract: Selection of topsoil alternatives is very important for surface mined land reclamation in the region of topsoil shortage. This paper conducted research on the selection of topsoil alternatives from overburden of a surface coalmine in Inner Mongolia, which is located in the famous Hulunbaier grassland. The analysis of geological profile indicated the potential capability of Layers Ⅱ and Ⅲ to become topsoil alternatives. The samples of Layers Ⅱ and Ⅲ were taken from its original places, the weathering materials of Layers Ⅱ and Ⅲ were taken from dumps, and the original topsoil was also taken as control for comparison. Thus, five treatments including original topsoil, Layer II weathering material, Layer II, Layer III weathering material and Layer III were selected. The physical, chemical properties and heavy metal contents of these five soil materials were determined based on samples' analysis. Seeds germination of alfalfa and surface crust situation of these soil materials were also obtained from pot experiments to check their effectiveness as topsoil. The results showed that soil textures of Layer Ⅱ and its weathering material contained 94.75% and 62.32% of clay respectively, which were clay and silty clay. Such soil could be relatively good topsoil alternatives, but the aggregate contents were lower, the pH values were slightly higher (8.02 and 9.22 respectively), and some nutrients such as organic matter contents, rapidly available K and available P were deficient. The serious surface crust of Layer Ⅱ and its weathering material decreased emergence rate of seeds. Layer Ⅲ and its weathering material contained almost 100% of clay, which were brown and heavy clay soil, but they had lower aggregate contents, moderate pH values (7.75 and 7.83 respectively), rich available K and lower other nutrient contents. All the samples of the five soil materials had lower contents of heavy metals such as As, Cr, Cu, Ni, Zn and Pb, meeting with the first class of the national soil environment standard. The surface crust situation of Layer Ⅲ and its weathering material were not serious and had better emergence rate of seeds, which were all larger than 55%, compared with the 65% of control treatment and the 25% of Layer II. The results indicated that Layer Ⅲ had similar soil chemical and physical properties and better seed germination compared with the original topsoil, and could be good topsoil alternatives. The weathering material of Layer Ⅲ was the best for topsoil alternatives.