Development of planting substrates for ecological restoration using quarry waste

This study aimed to develop a novel artificial planting substrate (APS) using quarry waste to replace externally sourced soil in applications such as landfill cover systems and ecological slope restoration. This approach addresses the dual challenges of waste rock disposal and land resource scarcity. A four-factor, four-level orthogonal experimental design was employed to investigate the effects of polyacrylamide (PAM), weathered basalt, mudstone, and straw powder, with glutenite as the base matrix, on the physicochemical properties of APS and plant growth, with the objective of optimizing substrate composition. The results showed that pure glutenite was unsuitable as a planting substrate. PAM addition significantly improved the water-holding capacity and available nitrogen content of APS (p < 0.05), thereby promoting plant growth. However, when the PAM content exceeded 0.3% by mass, seed germination decreased; overall, 0.3% PAM was found to be the optimal level for plant growth. Weathered basalt significantly affected total phosphorus content (p < 0.05), and its relatively high cation exchange capacity promoted plant growth, with the best performance observed at a mixing ratio of 60%. Mudstone had only a limited effect on most measured parameters. A 40% mudstone content was most favorable for plant growth, whereas 60% significantly reduced organic carbon and available potassium contents (p < 0.05). Straw powder significantly improved APS porosity, moisture content, and chemical properties, notably increasing available phosphorus, available potassium, and organic carbon contents while reducing pH (p < 0.05). Multi-factor analysis of variance was performed to evaluate the effects of the four substrate components on 16 physicochemical parameters and to identify the optimal formulation. In the optimized APS, the dry mass ratios of PAM, weathered basalt, mudstone, and straw powder to glutenite were 0.3%, 60%, 40%, and 6%, respectively. These findings provide both a theoretical basis and technical support for the ecological restoration of quarry areas and the resource utilization of quarry waste.