This project builds on the findings of the previous Environment Agency-led project, Identification and development of a set of national indicators for soil quality. Gain a broad consensus across the UK soil science community on the suitability of potential indicators for soil monitoring in the UK.
Why have indicators of soil quality?
With regard to 'environmental interaction', the composition of drainage water from soil greatly influences stream and lake water quality within catchments. More detailed analysis of the same data set showed bulk density data in relation to land use for all soils (Sparling and Schipper, 2004) and only for silt loam soils (Sparling et al., 2000). The model is based on the assumption that bioavailability is related to the interaction of free metal ions with receptor sites of the organisms – the biotic ligands.
Soil organic carbon (SOC) is likely to be one of the minimum dataset of soil indicators for reasons unrelated to its value as an indicator of soil quality. Accompanying the reports was a delegate pack which set out the processes undertaken to date, the form of the challenge processes and methodology of SQI practices (ie the Tiered Approach). Member of consortia (with Defra, SEERAD, CCW, DOENI, EH, NAWAD, EN, SEPA,) The Agency is responsible for Soil Quality Indicators in the context of the soil function.
Soil quality' - The capacity of a specific soil to function, within natural or managed ecosystem boundaries, to support plant and animal productivity, to maintain or improve water and air quality, and to support resident health. to man. The use of sludge values (MAFF, 1993) as trigger values for total soil metal concentrations in an agricultural context was thought to be appropriate, particularly as a guide to assess the significance of rates of change (in combination with other measures approximate, such as aerial deposition).
Workable ranges and trigger values for soil quality indicators
The Environment Agency’s approach
The approach, outlined in the following sections, was based on the knowledge and understanding of similar work undertaken internationally (Sparling et al., 2003), together with the experience of the UK soil science community. This approach, involving internal and external experts, ensured that the diverse needs of both the consortium and the Environment Agency were met.
The challenge – testing the indicators
Of the 67 identified potential indicators, only a limited number turned out to be relevant for the interaction of the soil with the environment. Fully testing all the above indicators would be prohibitively expensive in terms of time and resources.
The tiered approach
These are likely to be significantly fewer in number and scale compared to Tier 2 sites. At Tier 1, sampling is initially expected every five years – or at a frequency to be determined through subsequent work.
Establishing the minimum dataset
Soil reaction as measured by pH
A soil pH of 6 is recommended for grazing livestock (MAFF, 1981), but the significant decrease observed over time is thought to have been exacerbated by a decline in liming practices (Skinner and Todd, 1998). This variation and low stability over time can also be used as an argument against using a soil pH meter as an indicator of soil quality (De Clerk et al., 2003).
Aggregate stability
Biological indicators, such as nutrient mineralization, are also affected by a decrease in aggregate stability (Webb et al., 2003). A measure of aggregate stability would also provide a better assessment of the physical quality of the soil in rocky soil.
Soil bulk density
The laboratory determination of soil bulk density is a simple and robust procedure (Hall et al., 1977). Nevertheless, the data suggest that land use will have a strong influence on soil bulk density.
Catchment hydrographs
Most of the previous research aimed to explain an effect (such as flooding) by a hypothesized cause (such as large-scale afforestation or other changes in land use). Furthermore, the effects of the variables affecting the hydrography (precipitation, land use and soils) can be identified separately.
Mineralisable nitrogen
For the purposes of this review, we are only interested in assessing soil quality for the. New Zealand uses PMN as their only biological indicator – specifically long-term fertility changes – in the minimum data set. Biological methods involve measuring the amount of mineral N released into the soil by microbial activity during incubation.
In contrast, PMN may be considered inappropriate as an indicator in MDS because it is so variable.
Soil macroporosity
By relying on bulk density data, one disadvantage of the macroporosity method is that, without careful handling, the intact cores are susceptible to damage and loss of soil volume during sample extraction, transport and handling (Hernanz et al., 2000). Regarding sampling location, one main problem in measuring physical parameters such as macroporosity is that they vary in position in the soil profile (Neves et al., 2003). Each combination should be considered for any combination-specific relationship that exists between sustainable land use and measured SQI (Shulka et al., 2003).
In an applied study of macroporosity as an indicator of physical soil quality in New Zealand, Sparling et al. 2003) defined macroporosity trigger values for two land use groups without distinguishing by soil type.
Olsen P
For Olsen P to be a useful soil quality indicator in a minimum data set and to have relevance to the soil function of environmental interaction, there must be an explicit link between measured values in the soil and likely impacts on broader environmental quality (cf. McDowell , 2001) ). However, this should be the role of an indicator in the minimum data set to highlight likely environmental risk, and it is clear that Olsen P-values were used to assess the potential for adverse effects on the wider environment (Jordan et al. , 2000). Change in soil Olsen P values. indicates an increase in the available P content of the soil and likely risk of nutrient enrichment for aquatic systems.
The last two methodologies used by Sparling et al. 2003a), by which trigger values for soil indicators could be derived, modeling was done to set a limit value and used expert judgment to derive response curves for changes in the Olsen P-level (on the x-axis) against soil quality (0-100) %).
Soil quality indicators: metals and organic micropollutants
Therefore, the relevance of the values for use in an SQI context, from an environmental risk perspective, is not clear. At any time, it is the available fraction of the total metal concentration that can interact with and influence soil life - that is, the amount of metal in the soil that is in equilibrium with the metal in the soil solution. The data below (Figure 2.3.8.5) for the plots receiving N, P, potassium (K), sodium (Na) and magnesium (Mg) fertilizers illustrates any additional effect of the fertilizer.
The prevailing environmental conditions, soil characteristics including soil properties and biota, and the properties of the compounds themselves – polarity, solubility, volatility – will determine the fate of chemicals in the soil (O'Neill, 1993; Moorman, 1996; MacLeod et al., 2001 ).
Total nitrogen
Measuring total soil nitrogen (N) provides an indication of the total amount of all forms of N in the soil and also of the size of the organic N reserves and the organic matter quality. As the C:N ratio increases, N mineralization decreases, providing an indication of the potential activity of soil microbial populations (White, 1987). Topsoil TSN may only provide a limited indication of the capacity of the N budget in the soil, due to the exclusion of a relatively large part of N in the coarse soil fraction.
Total N is an indicator of the total nitrogen content of the soil; also, when associated with SOC, it can provide an indication of the likely mineralizable nitrogen supply.
Soil organic carbon
While SOC is mainly located in the top 15 cm, pesticide leaching does increase at SOC levels below 3-4%. At a soil depth of 12 inches or more, there is little evidence of a trigger or breakpoint; at depths of 15 cm or less, pesticide leaching increases at SOC levels less than 3-4%. No unclear threshold at soil depth of 30 cm or more; at depths of 15 cm or less, pesticide leaching increases when SOC is less than 3-4%.
Water storage decreases with less than 4% SOC; and where soil depths are 15cm or less, pesticide leaching increases more sharply at SOC levels below 3-4%.
UK soil quality indicators: identification of minimum dataset
Over short periods (10 years), climate-induced SOC change in the European cropland ranged 0.2–0.8% (with a confidence of 90%). The temporal variability of SOC must be considered when attempting to detect a change in SOC. The minimum detectable change in SOC will be influenced by soil type and land use.
After model calibration, the criteria described in approach 2 of Sparling et al. 2003) can be marked in SOC distribution curves for each soil group.
Peer review
Technical workshop
From peer review by selected experts and workshop summaries from the technical workshop, trigger values were derived for some of the indicators in the minimum data set. Further, the trigger values should be seen in the context of interpretive information also collected on site about soil type, land use, etc. Triggers - the values or range of values above or below which a level of change is understood to be critical in terms of the suitability of the land for a specific use.
This information will enable changes in Olsen P values to be placed in the context of soil function of environmental interaction. For habitats, the trigger table from the Olsen P ratio below was thought to be reasonable in light of the lack of sensitivity of Olsen P at the lower limits. Although it was recognized by the group that OMPs responded to environmental pressure, their role as an indicator of soil function in environmental interaction was not clear.
The indicators
Trigger values for indicators
Road testing the indicators and triggers
The soil quality indicators and respective trigger values should be tested in a desktop pilot trial and field validation exercise. Minimum data set - minimum number of key soil quality indicators to be used for high-level policy issues. Department for the Environment, Transport and the Regions (DETR), Circular 02/2000, Contaminated land: Implementation of Part IIA of the Environmental Protection Act Methods for assessing land quality.
Soil quality monitoring in New Zealand: developing an interpretive framework. 2002) Identification and development of a set of national indicators for soil quality.
Summary of peer review meeting
Macroporosity OFF Tricky, although it would be great if it could be measured easily and cheaply. Point linked to area – 'intelligent sampling' (Chambers Pers. Comm.) Why do we want to monitor. Also to establish success criteria for the sampling program: 'What do we want it to do?'.
Delegate pack for technical workshop
Aggregate stability was not considered an appropriate criterion for use as a Tier 1 soil quality indicator. Bulk density was considered an appropriate measure for use as a soil quality indicator. The catchment hydrograph was not considered a suitable measure for use as a soil quality indicator.
The metals copper (Cu) and zinc (Zn) were considered suitable for use as indicators of soil quality.
Extrapolated datasets used at the technical workshop
