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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.
Soil profiles contain multiple layers, known as horizons, that are generally parallel to the soil surface. These horizons are distinguishable from adjacent layers by their changes in morphological properties as the soil naturally forms. The same soil horizons may be named and labeled differently in various soil classification systems around the ...
The solum (plural, sola) in soil science consists of the surface and subsoil layers that have undergone the same soil forming conditions. The base of the solum is the relatively unweathered parent material. Solum and soils are not synonymous. Some soils include layers that are not affected by soil formation. These layers are not part of the solum.
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.
Soil formation, also known as pedogenesis, is the process of soil genesis as regulated by the effects of place, environment, and history. Biogeochemical processes act to both create and destroy order within soils.
A stonelayer, or soil stonelayer, or stone line, is a three-dimensional subsurface layer, or soil horizon, dominated by coarse particles (>2mm), that generally follows (mimics) the surface topography (Sharpe 1938).
This is a somewhat arbitrary definition as mixtures of sand, silt, clay and humus will support biological and agricultural activity before that time. [47] These constituents are moved from one level to another by water and animal activity. As a result, layers (horizons) form in the soil profile.
A fragipan is a diagnostic horizon in USDA soil taxonomy. They are altered subsurface soil layers that restrict water flow and root penetration. Fragipans are similar to a duripan in how they affect land-use limitations. In soil descriptions, they are commonly denoted by a Bx or Btx symbol. They often form in loess ground. [1]