Green waste compost as a substitute for turfy soil in external-soil spray seeding substrate

The scarcity of turfy soil (TS), which is the most commonly used external-soil spray seeding (ESSS) substrate component, has recently increased. The aim of this study was to introduce a substitute for TS as an organic matter additive in substrate. Green waste compost (GWC) that was combined with sandy loam soil, polyacrylamide (PAM), and super absorbent polymer (SAP) was used for preparing the soil substrate. Further, a modified soil-spraying experiment and artificial rainfall experiments with an orthogonal design (L₁₆4³) were conducted. These experiments assessed the feasibility of GWC as a component of ESSS substrate and the optimal formulation. The results indicated that the degree of influence of the three factors controlling the amended substrate is GWC > PAM > SAP. GWC improved the physical and chemical properties of the substrate, as well as the seed germination rate and seedling growth. Significant improvements can be observed with respect to the soil bulk density, soil porosity, steady infiltration rate, and anti-shearing strength (p < .01). Additionally, the runoff and soil loss decreased under heavy rainfall. Except for the soil nutrients and seedling height, all other indicators of the GWC substrates were better than those of the commercially available TS substrates. Principal component analysis and range analysis revealed that the optimum values of various design parameters were 40% for the compost volume content, 200 g m^-3 for PAM and 100 g m^-3 for SAP. Based on these results, GWC can be considered to be an effective alternative to TS for ESSS.