The Countryside Survey is the UK's longest integrated national monitoring programme. It is effectively an audit of the state of the countryside of Great Britain and began in 1978, with soils monitored in subsequent surveys in 1998, 2007 and every year since 2019. The data collected for this programme provide valuable insight into how our plants, soil, woodlands and small water bodies have evolved over time. Soil organic matter, pH and bulk density data from the Countryside Survey were used to generate benchmarks for these soil health indicators. It represents a nationally representative sample of our countryside and is used for a wide range of national statistics and reporting e.g. by the Office of National Statistics.

More information can be found here on the website: https://countrysidesurvey.org.uk/

We have used the data to create national maps of many of these soil properties. These are available on the UK Soil Observatory website. Link to CS topsoil maps of GB: http://www.ukso.org/static-maps/countryside-survey-topsoil.html

Earthworm numbers were captured as part of a separate nationwide survey of all available data by UKCEH. Specifically, earthworms are counted in a 20x20x20 cubic centimetre spadeful of topsoil. This information is not as robust as the Countryside Survey data as it is not a structured survey capturing without bias from across the countryside. In these types of studies, the type of soil studied tends to be easy to access near towns and cities and for habitats of more general interest e.g. agricultural land.

More information can be found here: https://catalogue.ceh.ac.uk/documents/1a1000a8-4e7e-4851-8784-94c7ba3e164f

The habitats presented here reflect how the landscape has been grouped into common vegetation and land-use types.

Here, we excluded all areas of open water or bare rock (as these contain no soil whatsoever). We then grouped the two urban and suburban land classes into a combined urban and man-made habitat and saltmarshes and beaches, which represent coastal areas with few developed soils, into a saltmarsh and near shore sediment habitat. We do not have many samples in these two habitats; hence we do not show benchmarks for these environments.

Two habitats represent the broad types of farmlands: arable and horticulture covers cropland, and improved grassland represents pastoral farming where activities such as tillage, fertiliser and lime has been used to increased agricultural production. Currently we are unable to separate between permanent grassland and leys where land is switched between arable and grassland. However new continuous satellite data which can track the presence of machinery and bare soil will enable us to do this going forward. For land in this category, typical values will likely fall between arable and horticulture and improved grassland as management activities generally decrease soil organic matter, earthworm numbers and increase pH and bulk density.

Woodland is also divided into two distinct categories: conifer woodland which includes cone-bearing, needle-leaved trees such as pine, fir, larch and spruce; and broadleaved and mixed woodland which includes tress such as oak, hazel, sycamore, beech and ash.

Heathland, bracken & montane, acid grassland, and neutral & calcareous grasslands represent the various grasslands and shrublands outside of farms and woodlands. Upland wetlands and lowland wetlands capture the bogs, fens, marshlands and swamps that are typically seen in places like Britain's hills and mountains and the East Anglian Fens. However, we do not include the wetlands which are also deep peats. This may seem a strange exclusion, but water table height is one of the critical factors which define whether deep peat is at risk of being depleted and we do not have data on this from the data sources used. We hope to link to other initiatives mapping deep peat condition in the future.

The soil types presented here consider factors such as soil texture (how sandy, loamy or clayey the soil is), the total depth of the soil profile, whether the soil is carbon-rich (organic) or not (mineral), and if the soil is at risk of flooding in river valleys or at the coast.

Light, medium and heavy soils can be distinguished from one another based on their clay content. Specifically, we have classed light soils as containing less than 18% clay; medium soils as containing between 18 and 35% clay; and any soil with more than 35% clay as a heavy soil.

Shallow mineral soils include soils that are no deeper than 30cm. These are common over chalk bedrock and in the uplands, especially on steeper slopes that do not generally permit much soil profile development. They are at high risk of being lost to erosion.

Carbon-rich soils include those soils that are generally rich in soil organic matter (more than 20%) but are not deep peat profiles. They tend to be highly acidic, have low bulk density, and generally do not support earthworms. They have highly variable characteristics as the top layer of soil organic matter varies in depth which has a major influence on soil organic matter content, pH and bulk density. The important thing for users of the tool is to set your own baseline and then track any change over time.

River floodplain (also called alluvial) and coastal soils are those soils that are most likely to flood in river valleys and by the coast. They are at risk of structural damage from compaction when wet or erosion by scouring flood waters. At the coast, the soil chemistry may be impacted by changes in salinity from salt-rich sea water.

Urban and disturbed industrial soils cover soils that are man-made in origin or have become heavily modified over time. These include spoil tips and soils that have become heavily compacted or contaminated by industrial activity. Deep peat is the most carbon-rich soil type in the UK, with deposits several metres in thickness in some places. These two soil types have highly specialised issues which need a broader approach for monitoring, so we do not consider these in SOD.

It is possible to sub-divide the light, medium and carbon-rich soil types further based on how easily water drains away after becoming saturated from heavy rainfall or a high water table. However, in our analysis, drainage characteristics showed little detectable impact on the assessed soil health indicators.

We have explored many different elements of our climate and their impact on soil properties and the dominant factor which has the biggest impact is always rainfall

Here we use a long-term mean annual rainfall to remove the effect of differences between years. The data from from the UKCEH Climate, Hydrology and Ecology research Support System (CHESS) dataset, which covers the period of 01/01/1961 to 31/12/2017.

After dividing the landscape into different habitats and soil types combinations, we used statistical modelling to determine where it might be possible to distinguish land covered by a low rainfall regime from a high rainfall regime. Our modelling was able to identify splits between low and high rainfall for over 40 combinations of habitat and soil.

This division between low and high rainfall is unique for each habitat-soil combination as both soil and habitat affects the sensitivity of a soil to rainfall. The division is also affected by where these combinations occur in the country and the rainfall they experience in a typical year. Soils in low rainfall areas with vegetation which have high water needs on a very freely draining sandy soils may have a very different rainfall threshold compared to a habitat-soil combination which occurs in wet upland areas.

What's more, rainfall affects the individual soil health indicators in different ways. This means that for the same combination of habitat and soil type, splits between low and high rainfall regime will occur at different mean annual rainfall thresholds. And in some cases, a rainfall split will be identified for one or more soil health indicators, but not all of them. For example, arable habitats with heavy clayey soils can be split into two rainfall regimes for pH and bulk density, but not soil organic matter. This is both due to the different sensitivity of our methods to detect the split, the need for more data but also the fundamentally different response to rainfall and moisture availability.

Soil organic matter, pH, bulk density and earthworms provide physical, chemical and biological indicators of healthy soil functioning. They are easy to measure and reliably so for most environments in the UK.

They are also closely interrelated. For instance, soil organic matter is key to promoting soil porosity (which affects bulk density), maintaining a soil's buffering capacity (which links with pH), and is a major source of energy for living organisms including plants and creatures that live in the soil such as earthworms.

There are many other soil properties which are important for soil health which we hope to include going forward e.g. contaminants levels, soil aggregation, microbial metrics etc. Have your say in our feedback section.

We recognise every soil is different but some generalities can still be made based on factors which we know most influence soil health. One way of thinking about this is every person is different and yet we still provide benchmarks for simple metrics such as weight and blood pressure taking account of a few basic facts (age, sex, etc.). For soil, these basic factors which affect health are soil type, habitat and climate.

Ultimately, the critical point is for you to start creating your own benchmarks (i.e. your starting point for a field or piece of land) and track how that is improving or degrading your soil using these simple metrics. If you continue to sample your soil in the same way and use the same lab to analyse your soil in the same way - you will soon create your own way of tracking your soil. We recommend doing this on a 5 year cycle

We divided our data into different land classes by habitats; then by the soil types underlying each habitat; and where possible, between "low" rainfall or "high" rainfall classes where data indicated rainfall had an influence on the data.

For each one of these combinations of habitat, soil type and rainfall, we then calculated the "typical" values for SOM, pH, bulk density and earthworms i.e. those which sit in the middle 80% of all our data. The bottom 10% of our data were then classed as "below typical" and the highest 10% as "above typical". We are careful about not stating these above and below typical values as healthy or unhealthy as there is still much debate in the soil community about what should define a 'health' threshold. We hope that by providing a national range of values, users of the tool can at least benchmark themselves against typical national values. See the question below about what "typical" means for each soil health metric

When we say "typical", we presume that the status quo of a soil health indicator is typical for Britain's soils. Ideally, you would want your soil to be in the typical range for all soil health indicators. That said, geography may make it challenging to optimise your soil across these 4 dimensions. For example, your soil may have formed over highly acidic parent material which puts your soil pH in or near to the "below typical" range.

In general, more soil organic matter is better as this means more carbon storage in the soil, a greater availability of nutrients for plant growth, and less soil loss via erosion. Lower bulk density and larger earthworm populations are generally better too for similar reasons, especially on agricultural land where compaction can be a serious issue. Thus, soil organic matter that is considered "above typical" and bulk density that is considered "below typical" are usually interpreted positively for soil health.

Soil pH is a context specific issue. Ideally, we don't want croplands to be too acidic or too alkaline as this will limit nutrient uptake by plants. Meanwhile, our most carbon-rich soils tend to be highly acidic and intervening to make these more alkaline could be highly detrimental for carbon emissions and for local plant species that thrive best on acid soils.

Not all soil health indicators are measured at the same time and location. Bulk density measurements only exist for soil samples taken in the 2007 survey year onwards, whereas pH and soil organic matter measurements are available for 1978 and 1998 as well. Earthworm data is much more limited as these organisms are rare or non-existent in some habitats, particularly where it may be too cold and wet.

As a result, it's possible that your location may not show benchmarks for 1 or more soil health indicators. This is something that should change as more national monitoring survey data is collected in future years.

Soil is the largest store of organic carbon in the terrestrial environment, containing more than double the amount of carbon stored in the atmosphere. As such, soil has the potential to be a major carbon sink. For example, wetland soils are great stores of organic carbon as their low temperatures and high moisture levels slow down decomposition and release of any carbon to the atmosphere. But soil can also be a source of carbon losses as land use changes, for instance, from a woodland to a cropland. As the main component of soil organic matter, the benefits of organic carbon to soil structure and wider soil health are similar to soil organic matter.

For more information, see the following report:
The Royal Society (2020). Soil Structure and its benefits: An evidence synthesis. https://royalsociety.org/topics-policy/projects/soil-structure-and-its-benefits/ 66pp.

Nitrogen is one of soil's macronutrients (elements that plants need in relatively large amounts to grow) and is thus a fundamental indicator of soil fertility. Nitrogen levels have also been used as an indicator of unintended nitrogen enrichment of the soils managed for conservation following deposition of atmospheric nitrogen compounds from industry and agriculture across the landscape. This can cause significant damaging effects for native plants and the wildlife associated with them.

Nitrogen levels relative to carbon (the carbon-to-nitrogen ratio, or C:N) are also important for soil nutrient cycling. Soils with a C:N ratio of 24:1 are in optimal condition for microbes to release nutrients to crops, thereby enhancing agricultural productivity.

Like nitrogen, phosphorous is one of soil's macronutrients (elements that plants need in relatively large amounts to grow) and is thus a fundamental indicator of soil fertility. Without enough phosphorous, the growth of plant shoots can be slowed or even halted entirely. On the other hand, an excess of phosphorous in soils can build up over time through repeated use of manures or non-organic fertilisers. This can be an issue for some plants as it reduces their ability to take up iron and zinc. Soils that are richer in clay content have a greater capacity to hold phosphorous than siltier and sandier soils.

Phosphorous levels are often indicated by an indicator called "Olsen-P", an easily accessible form of phosphorous for plants. This fraction has traditionally been favoured for limed, fertilised agricultural soils and environments with neutral to alkaline pH soils. However, it is not considered appropriate for acidic soils in moorlands, wetlands and woodlands.

Soil mesofauna are small bugs and other organisms that are visible to the naked eye but are no larger than a grain of sand. They include mites, springtails and tardigrades. Like earthworms, they influence soil structure including its ability to hold moisture, and they affect how quickly nutrients are released from organic matter, thereby affecting the soil's productivity. The Countryside Survey has records for more than 30 broad taxonomic groups of soil mesofauna going back to 2000 across the breadth of habitats and soil types of Great Britain and maps are available through the UK Soil Observatory: http://www.ukso.org/static-maps/countryside-survey-topsoil.html

Soil erosion is the loss of topsoil from the land by running water or wind. Croplands are particularly susceptible to erosion, especially during fallow periods between the harvesting of one crop and the sowing of another, and if the soil is silty or lies on a noticeable slope. Soils that have been compacted and damaged by heavy machinery are also vulnerable.

Erosion is estimated to move about 2.2 million tonnes of topsoil per year in the UK alone, making the land locally less productive, but also contaminating water courses nearby. Defra have estimated that the total cost of erosion in England and Wales is in the region of £150 million per year. Keeping soils protected in fields using cover crops, as well as increasing soil organic matter content, reducing and preventing compaction, and maintaining healthy earthworm densities can all help to reduce soil erosion.

For more information, see the following report:
The Royal Society (2020). Soil Structure and its benefits: An evidence synthesis. https://royalsociety.org/topics-policy/projects/soil-structure-and-its-benefits/

The Countryside Survey has records for 13 heavy metals including cadmium, chromium, copper, nickel, lead, zinc, aluminium, titanium, manganese, arsenic, selenium, molybdenum and mercury. These records go back to 2000 and cover the breadth of habitats and soil types of Great Britain.

Some of these metals (e.g. zinc and manganese) are micronutrients (elements that plants need in very small amounts to grow) and can be useful indicators of soil fertility. However, if heavy metals are too abundant, they can make a soil toxic for plants and organisms. In extreme cases, river floodplain soils can be enormously enriched in heavy metals by contaminated soil and water from metal mining and processing further upstream. This contamination can persist well beyond human lifetimes, so a lot of river valleys in Wales, northern England, and Scotland with a history of metal mining may to this day have soils with toxic levels of heavy metals.

Soils can also be contaminated by pathogens and pesticides, and upland soils have in the past become enriched in radionuclides such as Caesium-137 by fallout from the Chernobyl nuclear plant explosion in 1986. More recently, attention has turned to microplastics (tiny waste products of larger pieces of plastic waste). These microplastics can enter the soil from sewage sludge that's been used as fertiliser. Once in the soil, microplastics can leach into groundwater or be ingested by soil organisms potentially reducing the benefit of their activity for soil.