Abstract: Reconstructing the soil matrix by covering coalmine spoils with soil is a key method for ameliorating the soil properties of the spoils, and accelerating vegetation recovery in minefields located in high-elevation frigid areas. In this study, a field experiment was conducted in the Shengxiong coal minefield at Muli, Qinghai Province. Field experiment treatments involved covering coalmine spoil with soil to four depths [0 (Control), 5, 10, and 15 cm] to identify the outcomes in each case and identify optimal vegetation restoration methods. Five forage species were trialed in this study: Elymus nutans, Festuca sinensis, Poa crymophila var. ‘Qinghai', Poa pratensis var. ‘Qinghai', and Puccinellia tenuiflora. It was found that ground cover of E. nutans was the highest among the tested species, and its height increased with time. The average vegetation cover after 3 years for the four soil cover treatments ranked: 15 cm (74.6%)>10 cm (70.8%)>5 cm (64.3%)>control (58.8%). During the study period, the difference in plant density between different treatments became progressively more significant. There was an extremely significant difference in the yield of aboveground biomass between the control plot and the soil-covered plots (P<0.01). The highest yield of aboveground biomass (453.6±38.4) g·m^-2 occurred in the treatment with 10 cm soil cover. This was nearly 2 times higher than in the control treatment. A significantly positive correlation was observed between soil nitrogen concentration and height (r= 0.578) and density (r=0.6198) of herbage (P<0.05). Similarly, there was an extremely significant positive correlation between aboveground biomass yield and soil available nitrogen content (r=0.839, P<0.01). In turn, soil organic matter content was significantly correlated with plot biomass yield (r=0.592, P<0.05). It is estimated that the cost of covering with soil to 5, 10 and 15 cm depth is, respectively, 20000, 40000 and 60000 CNY·hm^-2. The results demonstrate that soil covering can effectively promote plant growth and improve the height, ground cover and density of vegetation. Soil covering of mine spoil to 10 cm depth is an economical and effective method to restore the vegetation in open mining areas in alpine grassland.

Key words: soil covering, alpine mining area, vegetation restoration, herbage, coal mine spoils