Optimizing the formulation of external-soil spray seeding with sludge using the orthogonal test method for slope ecological protection

Abstract External-soil spray seeding has gradually become a widely used technology for slope ecological rehabilitation in China in the 21st century. Meanwhile, with ever-increasing amounts of municipal sewage sludge being produced, sewage sludge has become a new source of solid waste pollution in the environment. Therefore, the goal of this study was to utilize sludge as a new kind of spray seeding component to replace non-renewable turfy soil. Orthogonal experiments were conducted to optimize the substrate formulation regarding the four factors of soil-to-sludge ratio, fiber content, soil additive concentration, and bioorganic fertilizer concentration. The results showed that sludge improved the physical and chemical properties of the substrate, increased plant growth, and within a certain range of dosage, reduced runoff and soil loss. The improvements of soil bulk density, total porosity and soil nutrients were particularly notable ( P P Festuca arundinace performed best among the three plants ( P −3 .