Effects of coal gangue on soil property and plant growth in mining area

With indoor and outdoor treatments, coal gangue with different ratios (10%, 20%, 30%, 40% and 50%) and different particle sizes (0-2, 2-5, 5-8 and 8-10 mm) were mixed into soil, and formed reconstructed soil with different soil bulk densities (1.3, 1.35, 1.4, 1.45 and 1.5 g·cm^-3). The effects of soil reconstruction modes on soil water condition, structure stability of aggregate and the growth of Lolium perenne, Medicago sativa, and Trifolium repens were investigated. Soil saturated water (SW), capillary water (CW), and field water capacity (FC) were decreased with increasing coal gangue ratio, particle size, and bulk density of reconstructed soil. >0.25 mm particle size aggregate (R_0.25), mean weight diameter (MWD), and geometric mean diameter (GMD) increased first and then decreased with the increases of coal gangue particle size, reaching the peak at 2-5 mm coal gangue particle size. R_0.25, MWD and GMD were significantly and negatively correlated with coal gangue ratio. Based on boosted regression tree (BRT) model, the coal gangue ratio contributed 59.3%, 67.0% and 40.3% to the variation of SW, CW and FC, respectively, which was a main influencing factor of soil water content. The coal gangue particle size contributed 44.7%, 32.3% and 62.1% to the variation of R_0.25, MWD, and GMD, respecti-vely, which was the greatest influencing factor. Coal gangue ratio had a great effect on the growth of L. perenne, M. sativa, and T. repens, which contributed to 49.9%, 17.4% and 10.3% of their variations, respectively. Soil reconstruction mode of 30% coal gangue ratio and 5-8 mm coal gangue particle size was the best condition for plant growth, indicating that coal gangue could change soil water content and structure stability of aggregate. The soil reconstruction mode of 30% coal gangue ratio and 5-8 mm coal gangue particle size was recommended.