Indicators of Soil Resilience for Scotland and Northern Ireland
December 2005


Background to research
Considerable work has been carried out to date in terms of reviewing and developing indicators of soil quality and to a lesser extent, soil resilience. However, indicators have yet to be applied routinely to the assessment of functionality of soils, as determined by physical, chemical and biological properties. In particular, practical indicators have not yet been identified to enable assessment of the buffering function of soil and the interaction between environment and potential indicators of soil quality. There is increasing awareness of the threats affecting soils in Scotland and Northern Ireland and a growing need to be able to measure soil quality, resistance and resilience.

Objectives of research
Key findings
A set of headline, secondary and tertiary indicators for soil quality is proposed which included physical, chemical and biological indicators. Headline indicators are: (physical) soil depth above impermeable layer, topsoil total porosity/bulk density, subsoil permeability; (chemical) total soil organic matter (SOM), total soil N, C:N ratio, pH and Olsen P; (biological) microbial biomass C and potentially mineralisable N. The advantages and disadvantages of each indicator are discussed with reference to the soils of Scotland and Northern Ireland.

Soil resistance is defined as: "the capacity of a soil to continue to function without change throughout a disturbance". Soil resilience is defined as "the capacity of a soil to recover its functional and structural integrity after a disturbance". Sets of headline and secondary indicators for soil resistance and resilience are proposed. The headline indicators for soil resistance are: (physical) soil texture, bulk density and aggregate stability; (chemical) total SOM, soil pH and buffering capacity; (biological) microbial biomass C, presence of key microbial groups and soil respiration. The headline indicators for soil resilience are (physical) aggregate stability and soil structure; (chemical) buffering capacity; (biological) microbial biomass C, presence of key microbial groups and soil respiration.

The main sources of data on the soils of Scotland and Northern are listed in the report. This data allows us to assess the current (or relatively recent) state of Scotland's soils. However there is a shortage of soil physical data and an almost complete lack of biological data for soils in Scotland and Northern Ireland. Almost none of the available soil property information allows assessment of whether the status of measured parameters is acceptable or not. Similarly, the available data provides little indication of the soil’s ability to resist stresses or recover from them.

The extent or "health" of soil recovery is defined as the extent to which the functional capacity of the soil is restored or the extent to which the soil is delivering its full potential. It was not possible to establish thresholds for full (healthy) or no (unhealthy) soil recovery following a perturbation at this stage in terms of physical, chemical or biological indicators. Nor was it possible to define baselines for soil resilience for the chosen headline indicators with any degree of confidence given the nature and extent of available data. There may be some merit in setting preliminary baselines for soil resilience for the chosen headline indicators using expert group discussion where data exist (e.g. for some physical and chemical indicators). However, considerable further work is required before thresholds for soil recovery/no recovery can be set with confidence for the wide range of soil types present in Scotland and Northern Ireland.

The relative importance, in the Scottish and Northern Irish context, of the major threats identified in the EU Soil Framework Directive will depend on land use, soil types present and on local socio-economic drivers. It is important that the pressures and risks affecting soils in Scotland and Northern Ireland are identified and prioritised in order to facilitate choice of the most appropriate indicators (for soil quality, resistance and resilience) for use in specific situations and to optimise their effectiveness in protecting our soil resource.

Development of an interactive tool that quantifies the ability of soils to deliver identifiable environmental outputs was proposed. Development of such a tool will necessitate further research to identify the link between soil properties and the functions that they deliver.  In this report we have highlighted those soil properties that have proved to be most valuable in this context on the basis of current knowledge. However, this is a rapidly developing area, and as discussed in earlier sections there are many areas in which our current understanding is inadequate.

Recommendations for uptake
A risk-based approach to soil monitoring is proposed as being appropriate, considering the threats currently facing soils in Scotland and Northern Ireland. All indicators which are taken forward for development and/or inclusion in a new minimum dataset for use in assessing soil quality, resilience and/or resistance should as far as possible be sensitive, accurate, reproducible, interpretable, capable of rapid, high throughput and inexpensive. Further refinement of the proposed set of indicators is required in order to allow us to implement a programme of monitoring that will allow quantification of loss of soil quality and the resistance and resilience of soils to change.  The development of indicators for soil resistance and resilience is considered of greater importance than the development of indicators for soil quality. Future work on indicators should include development of new, cheap, rapid throughput chemical and biological methods which have been shown to be effective in recent studies.

Development of a minimum dataset of soil quality/resistance/resilience indicators should ideally be linked to a digitised national database containing reference values for physical, chemical and biological parameters in terms of good and poor soil quality and the resistance/resilience of different soil types under different land capability/land use classifications.  Ideally, this database should be available free or at low cost under licence to anyone wishing to use it. The availability of linked or stand-alone decision support tools to enable land managers, scientists, consultants, regulators and policy-makers to interpret soils data and asses the quality and health of soils status is vital if maximum use is to be made of the above digitised national database.

Copies of this report are available from the Foundation, in electronic format on CDRom at £20.00 + VAT or hard copy at £35.00, less 20% to FWR members.

N.B. The report is available for download from the SNIFFER Website