‘Soil quality’ encompasses the physical, chemical and biological properties of soil. These properties determine the ability of the soil to perform a variety of functions indicative of a healthy soil.
- Nutrient cycling – soil provides a habitat for the soil invertebrate and microbial communities required to break down organic materials and release the nutrients necessary to sustain growth. If the full range of invertebrates and microbes necessary to carry out these processes cannot function, plants and higher organisms will be unable to thrive within the ecosystem
- Water balance – soil acts as a store for water. A healthy soil will retain the water necessary to support the ecosystem, allowing infiltration of excess water to groundwater and preventing surface run-off and waterlogging
- Physical structure – soil will provide the physical medium to support vegetation, allowing adequate root development and the medium in which to hold water
- Pollution mitigation – soil acts as a buffer to pollution entering the system. The organic matter and clay constituents of soil allow pollutants to be immobilised within the system, reducing the risk of them being transferred to water bodies, vegetation and soil fauna.
Ultimately, these processes in combination will allow the whole ecosystem to function in a sustainable manner. For urban greenspace to be sustainable, the soil quality must be able to support both soil communities and vegetation. The presence of greenspace can serve to improve soil quality over time.
Greenspace is often established on previously disturbed soils, such as on former industrial land. These soils are often of poor quality, with low organic matter content and poor structure, sometimes containing contaminants that may limit ecosystem functioning. The creation of greenspace, often in combination with ground preparation (for example to reduce soil compaction) and the incorporation of soil amendments will allow the development of healthy soils over time. This achieved by:
- Establishing and managing vegetation to provide the organic inputs that are necessary to allow the soil ecosystem to flourish (for example through incorporating soil amendments and the supply of leaf litter and root exudates)
- Trees reduce the impact of heavy rainfall events, mitigating surface run-off of water into surface water courses
- The root systems of vegetation and the action of soil invertebrates such as earthworms improve soil structure, allowing infiltration of water.
The importance of soil quality is recognised by the UK Government, and a Soil Strategy (PDF-508K) for England has been produced by Defra. This strategy specifically mentions the role of urban greenspace in protecting soils in the built environment.
Greenspaces affect soil quality in urban areas in three main ways.
- Protecting existing soil quality. Where greenspace is already present, soil quality can be managed in a sustainable way. This can be achieved through the appropriate use of fertilisers and pesticides, planting species that help to improve soil fertility (e.g. nitrogen-fixing species), and maintaining vegetation cover to prevent soil loss
- Improving soil quality. The establishment of greenspace can be used to improve soil quality. This can include employing cultivation techniques to alleviate soil compaction and the natural creation of an organic matter soil layer through the cycling of organic materials
- Creating soils. Often the soil at a site will not be capable of supporting vegetation. Soil amendments can be incorporated into the existing soil to improve its fertility, water-holding capacity and microbial community.
These processes occur through natural soil development, or as a result of good management practices.
Forest Research Best Practice Guidance
van Herwijnen, R. and Hutchings, T. (2006). Laboratory Analysis and Soils and Spoils (PDF-294K). Best Practice Guidance for Land Regeneration, BPG Note 2. Forest Research, Farnham.
Foot, K. and Sinnett, D. (2006). Imported Soil or Soil-Forming Materials Placement (PDF-190K). Best Practice Guidance for Land Regeneration, BPG Note 5. Forest Research, Farnham.
Forest Research has extensive experience of conducting soil surveys and providing management options for soil creation and protection. We provide advice and recommendations on the sustainable management of soils and the use of soil amendments.
Forest Research has a long track record in conducting research on the establishment of greenspace on a variety of soil types, including the effects of soil quality on tree survival and growth, and of the use of fertilisers, soil amendments and pesticides on soil quality.