Why soil is important

Soil is linked to everything around us and performs many important roles in sustaining life on Earth. Soil plays seven key roles:

Providing the basis for food and biomass production

Unless sealed (covered over by roads, buildings, etc.), all soils support biomass production, whether it is natural vegetation or planted for agriculture and forestry. From the smallest seedling to the largest tree, all land-based vegetation depends on soil to provide them with nutrients, water and root support. In turn, this vegetation supports animal life on land.

The productivity of soil is dependent upon its physical and chemical conditions, as well as on climate. The most productive soils are usually used for arable farming and less productive soils support grassland, heathland and forests. Currently, around 75% of land is used for food production; however, future needs (e.g. biofuel production, urban development) may result in competition for this high quality agricultural land resulting in further pressure on soil.

Controlling and regulating environmental interactions- regulating water flow and quality

Soil and water quality are very closely linked and, to a significant extent, soil properties determine water quality. As water passes through soil it is filtered and purified which helps to generate clean and wholesome groundwater. This process also includes the removal of nutrients thereby reducing the risk of water eutrophication (the process by which water bodies become enriched by nutrients).

Soils also store water; in fact, Scottish soils can store more water than is held in all Scottish freshwater lochs. The storage of water and its slow release regulates water flow thereby reducing the risk of flooding.

However, soils have a finite capacity for storing water, nutrients and pollutants. Once the storage capacity is exhausted no further storage can occur. This can result in the excess being released from the soil, potentially resulting in water pollution or flooding.

Storing carbon and maintaining the balance of gases in the air

Soil organic matter is an extremely important component of soil. It improves nearly all soil properties (e.g. moisture retention, soil structure, drainage, nutrient storage) and therefore plays a vital role in many functions of soil.

The ability of soil to store carbon is important in reducing the amount of carbon dioxide (CO₂) in the atmosphere, thereby regulating climate change. Soil organisms continually breakdown complex organic molecules into simpler organic molecules and when the process is complete they are released as nutrients and gases, including greenhouse gases such as CO₂. However, soil organisms are also involved in a process called humification where new, more complex and stable organic matter is formed. In some soils, notably peats, organic matter breakdown does not occur completely owing to the high acidity and water content, which results in the accumulation of organic matter in the soil.

The amount of organic carbon in a particular soil is determined by the balance between carbon input to the soil (as organic matter) and carbon loss from the soil. On a global scale, soils contain about twice as much carbon as the atmosphere and about three times as much as vegetation. Scotland’s soils contain more than half of the UK’s terrestrial carbon and are therefore important carbon stores. A loss of 0.5% of this stored soil carbon would be roughly equivalent to Scotland’s annual greenhouse gas emissions.

The majority of CO₂ emissions from soil occur as a result of land use changes such as the draining or cultivating of organic soils, or the conversion of grasslands to arable land. Any disturbance of organic soils by forestry operations or construction projects, for example, may also result in CO₂ emissions.

Soils are also an important source of the greenhouse gas nitrous oxide (N₂O) with fertilised agricultural soils being responsible for the majority of Scotland’s N₂O emissions. In addition, agricultural soils can be an important source of ammonia, which affects sensitive semi-natural habitats through eutrophication.

Providing valued habitats and sustaining biodiversity

A habitat is a place that provides an organism with everything that it needs to survive, including food and shelter. Soil is a very complex habitat, sustaining a diverse range of organisms both above and below ground.

Biodiversity is the term used to refer to all the variety of life on Earth. It consists of all species, varieties and genes living both above and below ground.

Biodiversity above and below ground is influenced and controlled by soil properties. Scientists believe that soil biodiversity is much higher than in any other terrestrial habitat, even rainforests.

Whereas above ground biodiversity is relatively well known and understood, most soil organisms are still unknown and not yet scientifically described. The largest group of soil organisms are micro-organisms such as bacteria and fungi. It is believed that they may hold important genetic material that may be used for future drug development.

Providing a platform for buildings and roads

Buildings and infrastructure require land for their construction. The constant need for land for development has resulted in a gradual reduction in productive soil and land as they become permanently covered with roads and buildings.

Providing raw material

Soils provide a direct source of minerals and other resources. These include:

sand, gravel and stones for building;
ore for industry;
peat and coal for heating;
peat for horticulture.

Soils can cover or be built up on many of these raw materials; therefore, to get access to them the covering soil has to be removed.

Preserving cultural and archaeological heritage

Soil can conserve and preserve the archaeological record by forming a protective layer over archaeological sites and buried artefacts, ensuring their protection from potentially destructive elements like wind and rain. Landscape features such as cultivation terraces and rig and furrow resulting from historic land use also form part of our cultural heritage. These features may require some form of maintenance over time to ensure their survival as a result of considerate soil management.