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In soil classification systems, topsoil is known as the O Horizon or A Horizon. [8] [9] Soil horizons are layers parallel to the soil surface whose physical, chemical and biological characteristics differ from the layers above and beneath. The depth of the topsoil layer is measured as the depth of the surface to the first densely packed soil ...
The A horizon is the top layer of the mineral soil horizons, often referred to as 'topsoil'. This layer contains dark decomposed organic matter, which is called "humus". The technical definition of an A horizon may vary between the systems, but it is most commonly described in terms relative to deeper layers.
Humus has a characteristic black or dark brown color and is an accumulation of organic carbon.Besides the three major soil horizons of (A) surface/topsoil, (B) subsoil, and (C) substratum, some soils have an organic horizon (O) on the very surface.
The soil suborders within an order are differentiated on the basis of soil properties and horizons which depend on soil moisture and temperature. Forty-seven suborders are recognized in the United States. [6] The soil great group category is a subdivision of a suborder in which the kind and sequence of soil horizons distinguish one soil from ...
Soil scientists use the capital letters O, A, B, C, and E to identify the master horizons, and lowercase letters for distinctions of these horizons. Most soils have three major horizons—the surface horizon (A), the subsoil (B), and the substratum (C). Some soils have an organic horizon (O) on the surface, but this horizon can also be buried.
By passing from a horizon to another, from the top to the bottom of the soil profile, one goes back in time, with past events registered in soil horizons like in sediment layers. Sampling pollen , testate amoebae and plant remains in soil horizons may help to reveal environmental changes (e.g. climate change, land use change) which occurred in ...
Soil is made up of layers called soil horizons, these make up a vertical soil profile.There are five master horizons O, A, E, B, and C. The O horizon contains organic matter, A is considered the topsoil, E is present or absent depending on the type of soil and conditions, B is the subsoil, and C is unconsolidated rock.
The term humus form is not the same as the term humus.Forest humus form describes the various arrangement of organic and mineral horizons at the top of soil profiles. [1] It can be composed entirely of organic horizons, meaning an absence of the mineral horizon. [2]