Soil horizon
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A soil horizon is a layer parallel to the soil surface whose physical, chemical and biological characteristics differ from the layers above and beneath. Horizons are defined in many cases by obvious physical features, mainly colour and texture. These may be described both in absolute terms and in terms relative to the surrounding material, i.e. 'coarser' or 'sandier' than the horizons above and below.
A cross section of a soil, revealing horizons
Surface runoff, a potential pathway for nonpoint source pollution, from a farm field in Iowa during a rain storm
Albic Luvisol – dark surface horizon on a bleached subsurface horizon (an albic horizon) that tongues into a clay illuviation (Bt) horizon
Soil profile of a road in Bengaluru
Soil
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Soil, also commonly referred to as earth or dirt, is a mixture of organic matter, minerals, gases, liquids, and organisms that together support the life of plants and soil organisms. Some scientific definitions distinguish dirt from soil by restricting the former term specifically to displaced soil.
Surface-water-gley developed in glacial till in Northern Ireland
Soil measuring and surveying device
A, B, and C represent the soil profile, a notation firstly coined by Vasily Dokuchaev (1846–1903), the father of pedology. Here, A is the topsoil; B is a regolith; C is a saprolite (a less-weathered regolith); the bottom-most layer represents the bedrock.
A soil texture triangle plot is a visual representation of the proportions of sand, silt, and clay in a soil sample.