Effects of different land use types on soil structure and hydraulic characteristics of reclaimed coal mines in semi-arid areas

In order to explore the water characteristics of soil in reclaimed coal mines in semi-arid areas and make better use of the land in reclaimed mining areas, the basic physical properties, water characteristic curves, unsaturated water conductivity and water diffusion rate of the reclaimed mining areas were selected for four types of land use after the four land use modes of reclaimed mining areas: farmland, grassland, forest land and bare land. The results showed that the soil in the reclaimed mining area was sandy soil, with the highest porosity and water content of forest land, the lowest bulk density and clay content, the highest organic matter content in cultivated land and the lowest organic matter content in bare land. The content of sand grain in bare land is relatively high, and the powder content of cultivated land, grassland and forest land is relatively high, indicating that the mechanical composition of soil in mining area can be improved by three land use methods: returning land, grassland and forest. The Van-Genuchten (V-G) model could fit the soil moisture characteristic curve in the mining area well, the coefficient of determination R² was greater than 0.99, the gravity water of the soil capillary decreased significantly with the increase of water suction, and the water holding capacity in the suction section before 2.5 kPa was shown as cultivated land > grassland > bare land > forest land, and with the increase of suction, the water holding capacity of forest land was better than that of other land types. The water release process mainly appeared in the 0−4.8 kPa suction section, and the cultivated land had the best water release capacity and the worst forest land. Soil porosity and unsaturated water conductivity were significantly positively correlated, and the soil structure of four types of unsaturated water conductivity was the best in forest land > bare land > arable land > grassland. The soil volume moisture content and water diffusion rate conformed to the empirical formula of D(θ)=Aexp(Bθ) and changed exponentially, and the water diffusivity D(θ) increased exponentially with the soil volume moisture content θ, and R² was greater than 0.92, and the potential water transport capacity of forest land was the best, and the water diffusion rate of bare land changed the fastest with moisture content. The research results provide theoretical and data support for land use and ecological restoration of reclaimed coal mines in semi-arid areas.