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The WRB lists 40 diagnostic horizons. In addition to these diagnostic horizons, some other soil characteristics may be needed to define a soil type. Some soils do not have a clear development of horizons. A soil horizon is a result of soil-forming processes (pedogenesis). [5] Layers that have not undergone such processes may be simply called ...
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 ...
Influenced primarily by soil forming processes over time, it commonly forms below an albic horizon. It has less clay content than an argillic horizon but is still a visible layer. [3] In the pedogenesis process under a chronosequence, once the soil develops into an alfisol, the Cambic horizon will develop into an argillic (Bt) horizon.
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.
Soils are the product of climate, organisms and topography, acting on parent (geologic) material over time. Thus the great diversity of geologic materials, geomorphic processes, climatic conditions, biotic assemblages and land surface ages in the United States is responsible for the presence of an enormous variety of mineral and organic soils.
Soil animals, including fauna and soil mesofauna, mix soils as they form burrows and pores, allowing moisture and gases to move about, a process called bioturbation. [75] In the same way, plant roots penetrate soil horizons and open channels upon decomposition. [76]
No soil profile has all the major horizons. Some, called entisols, may have only one horizon or are currently considered as having no horizon, in particular incipient soils from unreclaimed mining waste deposits, [185] moraines, [186] volcanic cones [187] sand dunes or alluvial terraces. [188]
In terms of soil horizon designations, a solum consists of A, E, and B horizons and their transitional horizons and some O horizons. Included are horizons with an accumulation of carbonates or more soluble salts if they are either within, or contiguous, to other genetic horizons and are at least partly produced in the same period of soil ...