Topsoil alternatives selection for surface coal-mined land reclamation in Inner Mongolia, China: an experimental study

There are many surface coal mines located in Inner Mongolia, which has dry and scarce topsoil, and the selection of topsoil alternatives is key to coal-mined land reclamation. This study used the largest surface coal mine in the Holonbuyr grassland as the experimental site. The soil of layer II (loess) and layer III (mild clay) under the local topsoil, which has a high clay content and good texture, has the potential to be a substitute for topsoil. To reduce its viscosity and improve its nutrients, soil amendments mixed with organic matter, such as corn stalk and sheep and cattle manure and microbial agents, were added to four mixed substrates with different formulas. Twelve topsoil alternatives were produced and compared for further research. The results show that (1) by mixing a variety of substrates, topsoil alternatives can fully meet the alfalfa (Medicago sativa L.) growth requirement. (2) The addition of exogenous organic matter and microbial agents could significantly increase the nutrient content and the number of microorganisms in the soil, thereby increasing the plant height of alfalfa (Medicago sativa L.) and the average dry mass of the aboveground and underground parts