Humus

Humus [ Botany - Agronomy - Horticulture ]	Dictionary of botanic terminology - index of names
Derived terms: Humification Adjective: Humic

The dark, loamy, organic portion of the soil remaining after prolonged microbial decomposition.

Humus is a general term used to indicate the more or less complex organic substance resulting from the decomposition of plant and animal residues in a process called humification that forms the organic portion of soil. It is a dark coloured (brown or black) stable form of organic matter that remains after most of plant or animal residues have decomposed and mineralized. Generally, the decomposition has proceeded sufficiently to make it amorphous (it has decomposed sufficiently so that the source material is no longer recognizable) and relatively stable (it resists further decomposition because it is chemically protected/resistant). Humus mixes with top layers of soil (rock particles), supplies some of the nutrients needed by plants and increases acidity of soil (many inorganic nutrients are more soluble under acidic conditions, become more available). Humus modifies soil texture, coating mineral particles and holding them together; creates loose, crumbly texture, that allows water to soak in and nutrients retained; permits air to be incorporated into soil. Humus is extremely important to the fertility of soils in both a physical and chemical sense and is a major source of nutrients for soil organisms and plants.
Often incorrectly referred to as any decomposing organic material including sawdust, ground bark and manure.

To humify (Transitive & intransitive verb humifies, humified, humifying)


	*To make or turn into humus.*

Humification

The process of the formation of humus

The process of decomposition whereby organic material is humified and becomes and converted to humic substances through biochemical and abiotic processes.
Also used to evaluate the degree of decomposition of organic matter. Three degrees of humification are recognized in organic soil materials: fibric, hemic and sapric.

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Holdfast roots [ Botany ]
Dictionary of botanic terminology - index of names

Some species of climbing plants develop holdfast roots which help to support the vines on trees, walls, and rocks. By forcing their way into minute pores and crevices, they hold the plant firmly in place.

Climbing plants, like the poison ivy (Toxicodendron radicans), Boston ivy (Parthenocissus tricuspidata), and trumpet creeper (Campsis radicans), develop holdfast roots which help to support the vines on trees, walls, and rocks. By forcing their way into minute pores and crevices, they hold the plant firmly in place. Usually the Holdfast roots die at the end of the first season, but in some species they are perennial. In the tropics some of the large climbing plants have hold-fast roots by which they attach themselves, and long, cord-like roots that extend downward through the air and may lengthen and branch for several years until they strike the soil and become absorbent roots.

Major references and further lectures:
1) E. N. Transeau “General Botany” Discovery Publishing House, 1994