Humus

The humus , sometimes named topsoil , indicates the roadbase of the ground created and maintained by the decomposition the Organic matter, primarily by the combined action of the Animaux, the Bactérie S and the Champignon S of the ground. The humus is a flexible and aired matter, which absorbs and retains well the Eau, of pH slightly Acide, of dark aspect (brownish with black), with odor characteristic varying according to whether it is about a forest humus , of Prairie, or ground cultivated. The humus is different from the Compost. In the compartment of the Biosphere which is the ground, the humus of it is the part biologically most active. It is most present in moderated zone, but there is recently redécouvert and studied a kind of old humus and human origin in Amazonia; the “Terra lent” . The humus is absent from Désert S.

The slow and natural decomposition of a humus releases directly with the root S of the plants of the Azote, the Phosphore and all the nutritive elements essential to the growth of the Végétaux. If the humus is hidden by Labor or is asphyxiated (durable Inondation, compression, covering seals), it is degraded or dies and released quickly in pore water of the ground its nitrogen and part of its chemical elements by mineralizing and by losing its properties.

Before the Microscope does not highlight the fact that they are micro-organisms and Invertébrés which produce the humus, he was regarded as an inert chemical substance; the Dictionary Littré, of the French language (1872-1877) defines it as “topsoil” and gives some the following under-definition: “Term of Chemistry. Brown matter not very water soluble, soluble in the Alkali S, coming from the decomposition and slow combustion from the organic substances in the ground or at its surface” .

Agronomist S as Claude Bourguignon alerted as of the years 1970 on the loss and degradation of the humuses of the plowed agricultural zones, in the whole world, with like consequence a progressive reduction in the outputs, even (and sometimes especially) by compensating for these losses by artificial fertilizers, and an increase in the erosion of the grounds.

Etymology

The Latin word humus indicating the ground is quoted by Curtius (Ier century a. J. - C.) like coming from a Greek word meaning “ with ground ”, locative of substantive out of use.

Formation of the humuses

It is known as “biogenic” , i.e. the humus cannot be formed by simple oxidation of the Nécromasse in the absence of living organisms. The organic matter which is at the base of the humus is of primarily vegetable origin, then fungic and animal during the process of transformation, whereas the components of the deep ground are mainly of mineral origin. The raw material of the humus is the Litière, to which are added components of animal origin deposited on the surface horizon (name given to the surface of the ground by the pedologists) or re-installed by the digger animals, of which the Vers of ground. This matter undergoes a more or less fast evolution (according to the conditions of Température, moisture, acidity or the presence of inhibiters such as certain heavy metals or poisons) which leads to its transformation into mineral matter in the form of electronegative complex Colloïdes, stable and insoluble.

The organic matter which while breaking up produced the humus is made up;

  • of plants and Pollen S in decomposition,
  • of Excrement S and Exsudat S (Mucus, Mucilage S) of worms of ground and other animal and/or fungic organizations,
  • of the animal corpses and many micro-organisms, microscopic mushrooms and microbes,
All these elements are unceasingly digested, moved (Bioturbation) and are mobilized by a community of organizations known as Détritivore S or Saprophyte S, whose Bactérie S, Champignon S, Invertébré S and Arthropode S. In cold or continental zone, the formation of the humus is accelerated with the Printemps when the temperature goes up and that moisture is important.

The humus can accumulate and evolve/move very slowly under cold climate, until constituting one of the elements of the Puits of carbon, but in hot climate, it can evolve/move very quickly, even to mineralize themselves and disappear when it is exposed to the sun and that water misses. It is generally absent from rainy tropical forests, but the man locally produced an equivalent of the humus there known as Terra lent.

The humus constitutes a reserve from approximately 10 to 30 cm of organic matter in the ground, sometimes more. It is useful for the farmer, the gardener or the forester to know the total quantity of humus and its quality. One of the indices is the Rapport C/N ground. Odor and the visual aspect, as well as the observation under the microscope of the organizations the component inform about its quality, thus, if necessary that analyzes of its chemical composition.

One distinguishes from many components of the humuses and in particular of colloids, the fulvic acid and the humic acid , which disadvantage many pathogenic micro-organisms of the animals and plants. It is them which tint the water of a color " the" in certain tropical or moderate zones.

Types of humus

According to whether the humus were formed in a ventilated ground or rather asphyxiated (because for example of a total water saturation or a repeated compaction), one can classify the humuses between two extremes.

Humuses formed in aerobiosis:

  • the mull, with a good incorporation of the Organic matter and mineral matter carried out mainly by the Worms of ground, present in the Forests with intense biological activity and the Meadows;
  • the Moder, with a surface layer of Organic matter humified, nonbuilt-in, present in the Forests and the moors at average biological activity;
  • the Mor, with a surface layer of not or not very humified Organic matter (very similar to the Peat, from where its etymology), present in the forests and moors with weak biological activity.

Pseudo-humuses formed in anaérobiose:

Complex Argilo-humic

See also: Complex argilo-humic

The argilo-humic complexes (or CAH ) are consisted the association of Argile and humus, both in a state flocculated following the work of the micro-organisms of the ground, and in particular of the Vers of ground, which thanks to a special body of their digestive tract can bind these molecules which are negatively polarized by an ion with positive bipolarisation; the Calcium (Ca++). It seems that mucuses of certain organizations can also play a part in the constitution of these complexes which are stable and insoluble and which explains the resistance of the humus to water and erosion and the maintenance of its structure and its exceptional capillarity.

These complexes can moreover fix heavy metals, possibly radioactive, by limiting their transfer to the plants and water, with the food chain.

Destruction of the humus

The contributions of Biocide S, Pesticide S and Engrais can degrade or kill the humuses.

The ploughing kills the humus by hiding it, causing a too fast mineralization of the organic matter and losses of ground which reach usually 10 tonnes/an/hectare in moderate zone and until several hundred tons in tropical zone.

The disappearance of the humus also results in a phenomenon of glacis plowed grounds which strongly decreases their capacity to absorb water. This one, polluted by the Pesticide S and of excesses of Nitrate S (persons in charge of the pullulation of visible green Alga S on the ground) streams by carrying the fine particles which increase the Turbidité rivers and rivers.

See too

  • farming Pedology
  • Cycle of the nitrogen
  • Cycle of carbon
  • Technical simplified

External bonds

Filmed conferences:
  • Conference (filmed) of Claude Bourguignon, 1st part
  • Conference (filmed) of Claude Bourguignon, 2nd part
  • Short interview of C Burgundian, on site, in the course of observation of a ground cultivated

Simple: Humus

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