![]() ![]() Additionally, due to weathering, oxides (mainly iron oxides) and clay minerals are formed and accumulated. O) Organic surface layer: Plant litter layer-the upper part is often relatively undecomposed, but the lower part may be strongly humified.Ī) Surface soil: Layer of mineral soil with most organic matter accumulation and soil life. ![]() When examining soils in the field, attention must be paid to the local geomorphology and the historical uses, to which the land has been put, in order to ensure that the appropriate names are applied to the observed horizons. Soils with a history of human interference, for instance through major earthworks or regular deep ploughing, may lack distinct horizons almost completely. Not all of them are present in every soil. In the following, the horizons and layers are listed more or less by their position from top to bottom within the soil profile. Most individual systems defined more horizons and layers than just these five. An underlying loose, but poorly developed horizon is called a C horizon. If a well-developed subsoil horizon as a result of soil formation exists, it is generally called a B horizon. The mineral soil usually starts with an A horizon. Many soils have an organic surface layer, which is denominated with a capital letter "O" (letters may differ depending on the system). Layers that have not undergone such processes may be simply called "layers". Some soils do not have a clear development of horizons.Ī soil horizon is a result of soil-forming processes ( pedogenesis). In addition to these diagnostic horizons, some other soil characteristics may be needed to define a soil type. the "cambic horizon" or the "spodic horizon". Diagnostic horizons are usually indicated with names, e.g. Other systems pick out certain horizons, the "diagnostic horizons", for the definition examples are the World Reference Base for Soil Resources (WRB), the USDA soil taxonomy and the Australian Soil Classification. The German system uses entire horizon sequences for definition. In most soil classification systems, horizons are used to define soil types. ![]() Due to the different definitions of the horizon symbols, the systems cannot be mixed. ![]() No one system is more correct-as artificial constructs, their utility lies in their ability to accurately describe local conditions in a consistent manner. There are many different systems of horizon symbols in the world. Suffixes, in form of lowercase letters and figures, further differentiate the master horizons. Master horizons (main horizons) are indicated by capital letters. The identified horizons are indicated with symbols, which are mostly used in a hierarchical way. 'coarser' or 'sandier' than the horizons above and below. These may be described both in absolute terms (particle size distribution for texture, for instance) and in terms relative to the surrounding material, i.e. Horizons are defined in many cases by obvious physical features, mainly colour and texture. A cross section of a soil, revealing horizonsĪ soil horizon is a layer parallel to the soil surface whose physical, chemical and biological characteristics differ from the layers above and beneath. ![]()
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