Optimizing the properties of artificial phyllite soil through diverse microbial agents and environmental conditions

Phyllite has been widely available, directly accessible, and free from heavy metal contamination. It is often required for the investigation into the sourcing of restoration materials and the ecological environment over multiple temporal and spatial scales in mining areas. Among them, the ecological restoration of mining areas can involve backfilling mine pits with artificial soil in the Qinling region. It is crucial to select the optimal soil-building materials. Conventional materials like coal gangue—a byproduct of mineral extraction—contain heavy metals to hinder ecological restoration. In this study, soil cultivation, potted plant, and wilting experiments were conducted to compare optimal conditions for the weathered phyllite artificial soil. Soil quality indices (soil bulk density, pH values, maximum water-holding capacity, and electrical conductivity) were calculated for each combination of weathered phyllite artificial soil. Optimal parameters were identified using variance analysis. Key variables were also determined to enhance the reliability of the optimal parameters. Furthermore, two-dimensional interpolation of biomass and germination rates was also carried out to validate the optimization. The results revealed that microbial inoculants significantly improved the physicochemical properties of weathered phyllite artificial soil. The optimal combination of treatment was 60g of straw composting agent (JG) for 60-day cultivation. The bulk density of artificial soil stabilized at an ideal range near 1.22g/cm³, with the moderate pH and electrical conductivity close to that of natural soil. Notably, the maximum water-holding capacity reached 50.87%, with a 38% increase over natural soil, indicating the superior water retention and drought resistance. Pot experiments further validated that this treatment group achieved the highest germination rate (92%) of Bermuda grass seed and high biomass levels. Field verification revealed that crop germination rates and growth conditions significantly outperformed in the plots with this artificial soil, compared with the control group. There was a consistent trend over all measured parameters. Specifically, the bulk density shared a progressive decrease over the cultivation period, eventually plateauing at the optimal 1.22 g/cm³ within the ideal range for root growth and water infiltration. The pH values stabilized between 6.5 and 7.2, which was a neutral to slightly acidic environment conducive to nutrient availability and microbial activity. Low electrical conductivity remained on the minimal salinity stress for plant development in restored sites. The maximum water-holding capacity of 50.87% was enhanced by 38% over the local natural soil. The key factor was reduced irrigation demands for seedling survival during dry periods. The pot experiments validated that the 92% germination rate was accompanied by seedling growth. Two-dimensional interpolation of biomass and germination showed that the 60g JG 60-day cultivation point also represented the peak performance. The finding can provide the preliminary theoretical support for the practical needs in ecological conservation, restoration, and sustainable ecosystems. The optimal artificial soil formula can also offer practical, effective, and locally sourced solutions to significantly accelerate the ecosystem recovery in the mining areas.