Microbial Fertilizers and Shading Contribute to the Vegetation Assembly and Restoration of Steep-Slope after Soil Spray-Sowing in the Yuanjiang Dry-Hot Valley Region

Road construction and strip mining in mountainous regions inevitably causes the destruction of vegetation and soil, leading to large ranges of exposed slopes. Although soil spray-sowing has become a promising method to accelerate community assembly in humid regions, the application of microbial fertilizers and shading in slope recovery during soil spray-sowing are rarely reported in dry-hot valleys. This study compared the effectiveness among artificial seeding, arch column + planting bags, and soil spray-sowing by slope restoration trials in the Yuanjiang dry-hot valley, southwest China. Additionally, we explored the effect of slope degrees, shade, and microbial fertilizers on seedling survival and growth after soil spray-sowing. Results indicated that soil spray-sowing displayed better species survival and growth performance than artificial seeding and arch column + planting bags. The richness, density, and height of seedlings dropped dramatically with the increasing of slope degrees after soil spray-sowing, especially when the slope degree was greater than 1. Although shading observably improved the species density, it inhibited the growth of Albizia julibrissin and Crotalaria pallida. Moreover, microbial fertilizers Penicillium chrysogenum and Bacillus aryabhattai markedly enhanced the density and growth of species Azadirachta Indica, Cajanus cajan, Indigofera cassioides, and Sophora xanthanth. Soil spray-sowing, combined with shading and microbial fertilizers, contributes to species survival and growth when the slope degree is less than 1.73 and the soil spray-sowing process coincides with the rainy season, which provides the theoretical basis and technical support for ecological restoration in the dry-hot river valley.