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Horizon

Single layer in soil profile with similar properties or material but which differs at least in one property, e.g. colour or texture from adjacent horizons above or below in the profile; diagnostic horizon: Dominant soil property or material defines name of horizon, e.g. gypsic horizon having distinct calcium sulfate (gypsum: CaSO4) enrichment; genetic horizon depending on the type of pedogenesis.


Humification

Process whereby the carbon of organic residues is transformed and converted to humic substances through biochemical and abiotic processes.


Humus

Organic compounds in soil, exclusive of undecayed plant and animal tissues, their partial decomposition products, and the soil biomass; a term often used synonymously with soil organic matter, its structure is amorphous, specific weight is low and surface area high. Humus is important for soil fertility, and helps to bind soil particles and aggregates together.


Hydromorphic soils

Formed under conditions of poor drainage in marshes, swamps, seepage areas or flats.


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