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humus

humus (hyōō´məs), organic matter that has decayed to a relatively stable, amorphous state. It is an important biological constituent of fertile soil. 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 fertilizer). 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.

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humus

humus The dark-coloured amorphous colloidal material that constitutes the organic component of soil. It is formed by the decomposition of plant and animal remains and excrement (see litter) and has a complex and variable chemical composition. Being a colloid, it can hold water and therefore improves the water-retaining properties of soil; it also enhances soil fertility and workability. Acidic humus (mor) is found in regions of coniferous forest, where the decay is brought about mainly by fungi. Alkaline humus (mull) is typically found in grassland and deciduous forest: it supports an abundance of microorganisms and small animals (e.g. earthworms).

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humus

humus
1. Decomposed organic matter of soils that are aerobic for part of the year: it is dark brown and amorphous, having lost all trace of the structure and composition of the vegetable and animal matter from which it was derived.

2. A term used by some horticulturists to describe any kind of organic matter in the soil.

3. A surface organic soil horizon that may be divided into types, e.g. mor (acid and layered) or mull (alkaline and decomposed). It is the ‘histic epipedon’ of the USDA Soil Taxonomy. See also humification.

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humus

humus
1. Decomposed organic matter of soils that are aerobic for part of the year: it is dark brown and amorphous, having lost all trace of the structure and composition of the vegetable and animal matter from which it was derived.

2. A surface organic soil horizon that may be divided into types, e.g. mor (acid and layered) or mull (alkaline and decomposed). It is the ‘histic epipedon. See also HUMIFICATION.

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humus

humus
1. Decomposed organic matter in soils that are aerobic for part of the year. It is dark brown and amorphous, having lost all trace of the structure and composition of the vegetable and animal matter from which it was derived.

2. Surface organic soil horizon that may be divided into types: mor (acid and layered) or mull (alkaline and decomposed). It is now known as a ‘histic epipedon’.

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humus

humus Dark brown, organic substance resulting from partial decay of plant and animal matter. It improves soil by retaining moisture, aerating and increasing mineral nutrient content and bacterial activity. Types include peat moss, leaf mould, and soil from woods.

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humus

hu·mus / ˈ(h)yoōməs/ • n. the organic component of soil, formed by the decomposition of leaves and other plant material by soil microorganisms.

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humus

humus The semi-decomposed organic matter in the soil; it provides nutrients for plant growth and increases the water-absorbing capacity of the soil.

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humus

humus XVIII. — L., ‘mould, ground, soil’.

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humus

humus •Lammas • Cadmus • Las Palmas •chiasmus, Erasmus •Nostradamus •famous, ignoramus, Seamus, shamus •Polyphemus, Remus •grimace • Michaelmas •Christmas, isthmus •litmus •animus, equanimous, magnanimous, pusillanimous, unanimous •anonymous, eponymous, Hieronymus, pseudonymous, synonymous •Septimus •Mimas, primus, thymus, timeous •Thomas •enormous, ginormous •brumous, hummus, humous, humus, spumous, strumous •blasphemous •bigamous, polygamous, trigamous •endogamous, monogamous •calamus, hypothalamus, thalamus •venomous •autonomous, bonhomous, heteronomous •Pyramus •dichotomous, hippopotamus, trichotomous •Thermos

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