Materials for soil formation

Soil creation using materials containing potentially toxic contaminants must take into account their fate, whether in the soil, or beyond it in the vegetation or water flowing through it. In an urban context, soil formation will usually be driven towards creating a soil type that can sustain a particular type of vegetation. Soil-forming and other soil processes should also be considered when managing natural soil materials in urban greenspace schemes, in order to maintain soil sustainability and prevent soil degradation.

Background

Consideration of soil formation is important in the urban environment where greenspace is to be established, especially if the natural soil is inadequate and soil-forming materials – the basic building blocks of a soil – have to be used for vegetation growth. Artificial soil formation involves more than mixing these ingredients together. It requires an understanding of how soils are created naturally in order to encourage soil-formation processes to act as quickly and effectively as possible.

The term ‘soil-forming material’ has been employed for non-soil materials used in land reclamation to support vegetation growth. These are usually derived from mineral wastes, such as:

  • Overburden materials (i.e. soils lying above minerals of interest for mining)
  • Uneconomic geological materials encountered during quarrying or mining (spoils)
  • From the treatment or refinement of the mineral ores or raw products.

In addition, other industrial by-products, such as pulverised fuel ash or flue-gas desulfurisation (FGD) gypsum from thermal power stations, are sometimes used for this purpose.

Soil-forming materials must also have the propensity to turn into soils over time. This process can be encouraged by treatment to relieve compaction; the incorporation of organic matter such as greenwaste compost; and the choice of appropriate vegetation types that will endure and improve the quality of the substrate.

Practical considerations

In the urban context, artificial soil formation usually depends on four main sources of base materials:

  • Mineral materials in the ‘made ground’ on a site – usually a mixture of natural but degraded soil materials, together with waste materials disposed of on the site during industrial use
  • Naturally unconsolidated (or ground) geological materials – e.g. sands and gravels, mining overburden Specific waste materials from industrial processes – e.g. pulverised fuel ash, fines from washing plant
  • Remediated materials following application of soil remediation technologies – e.g. material resulting from soil washing, thermal desorption or bioremediation.

All four types are likely to be infertile and, depending on the specific source or land-use history, may have chemical or physical properties that are hostile to plants. They may also pose a risk of environmental contamination, depending on future use and the soil-forming technologies adopted. Soil formation using these types of material usually involves their amendment with organic materials to provide additional nutrient resources, and to help restrict contaminant movement and/or assist in their breakdown.

Further considerations

Effective artificial soil formation depends on good planning and assembling important information. This includes:

  • Physical and chemical properties of the proposed soil-forming materials and organic amendment materials, using involving laboratory analyses
  • Understanding of the edaphic qualities of the plant species proposed for planting
  • The risk of loss of potential contaminants, using a combination of leachate tests, bioassay testing and modelling
  • An understanding of the hydrological behaviour of the site where soil formation is to be executed, including assessments of likely risk of surface and groundwater contamination.

Case studies

Forest Research have been involved in two projects funded by EPSRC under the SUBR:IM (Sustainable Urban Brownfield Remediation: Integrated Management) Consortium.

The first, ‘Novel special-purpose composts for the sustainable remediation of brownfield sites’ developed a novel sustainable remediation technique that relies on the use of waste produced materials (composts) combined with naturally occurring minerals (clays, zeolites) to enhance the biodegradation and immobilisation capability of the compost. This was based on nursery trials to evaluate the effectiveness of the technology by monitoring the bio-availability of the contaminants of concerns to plants under specific experimental conditions.

The second, ‘Integrated urban remediation and greening’ aimed, amongst other objectives, to test the suitability of remediated soil materials for vegetation establishment.

A summary of the results from these two trials is available in a CL:AIRE SUBR:IM Bulletin ‘The use of compost in the regeneration of brownfield land(PDF-409K).

Services

Forest Research has over 40 years’ experience in establishing vegetation on brownfield sites, often where the existing soil resource is likely to limit sustainable plant survival and growth, and frequently provides consultancy and research services to the Forestry Commission and external clients.

Site investigation

Forest Research has extensive experience of conducting soil surveys, including evaluation of the soil resource.

Recommendations

Forest Research is available to provide advice and recommendations on the formation of soils on a range of substrates, and has experience of a variety of composts and other waste products as soil amendments.

Research

Forest Research has a long track record in conducting research on the use of soil-forming materials in land regeneration, including conducting batch leaching tests, nursery and field trials and ecotoxicological experiments to determine the suitability of potential materials for specific site conditions.

Further information

Forest Research Best Practice Guidance

Foot, K. and Sinnett, D. (2006). Imported Soil or Soil-Forming Materials Placement (PDF-191K). Best Practice Guidance for Land Regeneration, BPG Note 5. Forest Research, Farnham.

van Herwijnen, R. and Hutchings. A. (2006. Laboratory Analysis of Soils and Spoils (PDF-294K). Best Practice Guidance for Land Regeneration, BPG Note 2. Forest Research, Farnham.

Hutchings, A, Sinnett, D. and Doick, K. (2006). Soil Sampling Derelict, Underused and Neglected Land prior to Greenspace Establishment (PDF-956K). Best Practice Guidance for Land Regeneration, BPG Note 1. Forest Research, Farnham.

Additional information

Bending, N.A.D., McRae, S.G. and Moffat, A.J. (1999). Soil-forming Materials: Their use in Land Reclamation.Stationery Office, London.

van Herwijnen, R., Sellers, G., Sinnett, D., Moffat, A.J., Hutchings, T.R., Al-Tabbaa, A. and Ouki, S. (2008). The Use of Compost in the Regeneration of Brownfield Land (PDF-409K). CL:AIRE SUBR:IM Bulletin 10 (Contaminated Land: Applications in Real Environments/Sustainable Urban Brownfield Regeneration: Integrated Management.)


Glossary

Edaphic
Refers to plant communities that are distinguished by soil conditions rather than by the climate