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humus(hyo͞o`məs), organic matter that has decayed to a relatively stable, amorphous state. It is an important biological constituent of fertile soilsoil,
surface layer of the earth, composed of fine rock material disintegrated by geological processes; and humus, the organic remains of decomposed vegetation. In agriculture, soil is the medium that supports crop plants, both physically and biologically.
..... Click the link for more information. . Humus is formed by the decomposing action of soil microorganisms (e.g., bacteria and fungi), which break down animal and vegetable material into elements that can be used by growing plants. Technically, humus, as the end result of this process, is less valuable for plant growth than are the products formed during active decomposition (see fertilizerfertilizer,
organic or inorganic material containing one or more of the nutrients—mainly nitrogen, phosphorus, and potassium, and other essential elements required for plant growth.
..... Click the link for more information. ). Because of its low specific weight and high surface area, humus has a profound effect upon the physical properties of mineral soils with regard to improved soil structure, water intake and reservoir capacity, ability to resist erosion, and the ability to hold chemical elements in a form readily accessible to plants.
an organic, normally dark-colored part of the soil formed as a result of biochemical transformation of plant and animal residues. Humus consists of humic acids (most important for soil fertility) and fulvic acids (crenic acids). Humus contains the main elements of plant nutrition that become available to plants as a result of microbial activity.