Formulation and use of manufactured soils: A major use for organic and inorganic wastes

Manufactured soils are created as replacements for topsoils and are mixtures of organic wastes (e.g. green waste, bark and sawdust (composts) and inorganic materials such as sand or crushed rock. They are applied in bulk for landscaping purposes and in rehabilitation of wasteland, brownfield sites and mined areas. Specialized uses include soilless media for container-grown plants and bag and pot culture of glasshouse vegetable crops where high macroporosity is required to prevent waterlogging. For use in landscaping and rehabilitation, composted municipal green waste is the most commonly used base material. Small amounts (e.g. 10–30% v/v) of mineral material (e.g. sand, rock crushing grit, subsoil) are often added. The main ingredient for structural manufactured soils (which can provide support for large footpaths, small buildings, etc.) is coarse stone aggregate while sand can be the basis for high-traffic turf such as sports fields and putting greens. There is little interaction between organic and inorganic components in most manufactured soils. Use of a greater proportion of waste inorganic materials with chemically reactive surfaces such as blast furnace slag, steel furnace slag, bauxite residue, fly ash and water treatment residuals could result in greater linkage between components, greater aggregation into a newly-formed material and greater stabilization of the organic components. This would be desirable where sustainable long-term use of the material is required (e.g. in landscaping and rehabilitation) and future research in this area is needed.