ADLib Glossary (S)

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Soil and its Importance

Soil is a basic limited resource that will continue to be essential for many human activities. It includes both topsoil and subsoil to a depth of at least 1 metre. The biological, physical and chemical characteristics of soil need to be protected for it to perform its important functions. These include producing food, raw materials and energy. Soils also provide a filtering and buffering action to protect water and the food chain from potential pollutants; they help to maintain gene pools and wildlife populations; and they often cover historic and archaeological sites and contain artefacts and historical indicators such as pollen.

Soil types can be classified in a wide variety of ways. One common albeit simple approach is to classify by texture. There are seven main types: sandy, shallow, clay, deep silty, other mineral, organic mineral and peat.

There are many ways of classifying soils. A simple soil classification has been used is given here. The basic soil texture types are:

SANDY: Soils which are sand or loamy sand to 40 cm depth and are sandy to 100 cm. Soils which are sandy loam to 40 cm only are classified as Other Mineral.


CLAY: Soils with predominantly clay or clay loam topsoils overlying clay sub-soils.




PEAT: Soils that contain more than 20% organic matter derived from sedge or similar plant material.

See also:

Soils that are predominantly mineral but contain between 6 and 20% organic matter. These can be distinguished by darker colouring that stains the fingers black or grey and gives the soil a silty feel.Mineral soils that do not fall into any of the categories above.Soils of sandy silt loam to silty clay loam texture 100 cm depth.Mineral soils over chalk, limestone or other rock in which the parent material is within 40 cm of the soil surface. Sandy soils developed over sandstone should be regarded as sandy.
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