Statistical Evaluation of Sprayed Synthetic Soils Amended with Four Additive Factors Used in High- and Cut Rock Slopes

Abstract

There are many bare and cut rock slopes resulting from quarrying or highway engineering abandoned in China because of immature outside soil spray seeding (OSSS) engineering techniques. To improve properties of synthetic soil technique to spray on such slopes (gradient >50°), four components of OSSS, that is, cement, inorganic compound fertilizers (ICF), wood bits, and peat soil at four treatment levels for each were mixed into soil using orthogonal array designs OA16 (45). Relationships of each of four components with plant biomass, soil physicochemical and microbial features were explored to determine optimal synthetic soil combinations for OSSS techniques. Significant differences in plant biomass, soil physicochemical properties and microbial activities among 16 different OSSS synthetic soils with different contents of four components were identified. Optimal combination of N10 with higher nutrients (added with 0.8% ICF, 1.5% cement, 1.5% peat soil, and 2.0% wood bits) and N13 with highest viscidity (added with 0.4% ICF, 2.0% cement, 1.5% peat soil, and 2.0% wood bits) than other combinations were obtained to be used in OSSS sprayed soils to reconstruct the bare high- and cut rock slopes, which was supported by results of cluster analysis. On the other hand, based on canonical correlation analysis, redundancy analysis, and discriminant analysis, soil physicochemical properties explained 56.41% of the soil microbial activities and the cement is the most influential factor on soil properties. Among all tested indicators, soil NH4-N, total P, pH, organic C, phenol oxidase, invertase, CM-cellulase, acid phosphatase, alkaline phosphatase, and basal respiration were more responsive to OSSS synthetic soils. Our results have documented improvement of soil physicochemical and microbial features of the OSSS soil under the condition of 2.0% cement content.