Humus is characterized by a dark color that reflects its high carbon organic.

The humus, means the top layer of soil created and maintained by the decomposition of organic matter , mainly through the combined action of animals , from bacteria and fungi in the soil. Humus is a soft and airy, which absorbs and retains much of the water , the pH varies as organic matter is whether or not related to minerals, looking dark (brownish black), with characteristic odor ranging whether it is one of many forms of humus forest ^Etymology

The Greek word designating humus "earth" is mentioned by Curtius ^(first century AD.) as originating from a Greek word meaning "land" rental of a noun out of use.

In fact, the Latin word humus, as does the word homo "man" comes from the Indo-European root * ghyom, which meant land (cf. J. Picoche 1994, p. 287).

Formation of humus

The exposure of soil tillage and repeated in a few years causing a loss of humus. Black soils become tan, lose their ability to retain and infiltrate the water and become more susceptible to erosion.

The tillage and fertilizer chemicals are not the only causes destruction of the humus which sets soils; the deforestation and overgrazing of fragile soils are others. Unprotected vegetable soil, and without addition of organic matter, the erosion and depletion of this soil are inevitable

The formation of humus or humification is called "biogenic", that is to say that humus can be formed by simple oxidation of dead organic matter in the absence of living organisms, but this process is greatly accelerated when living organisms ingest organic material or secrete enzymes that transform.

The organic matter that is the basis of the original humus is essentially plant and microbial and animal during the transformation process, while components of the deep soil are largely of mineral origin.

The raw material of humus is either the litter or crop residues, combined components of animal origin deposited in the horizon surface (the name given to the soil surface by soil scientists ) or raised by animals burrowing, including earthworms. This material is changing faster or slower (depending on conditions of temperature , moisture, acidity or the presence of inhibitors such as heavy metals or toxic) that leads to his transformation into complex organic compounds, electronegative and relatively stable. Depending on the size of the molecules produced, these compounds insoluble ( humin ) or colloids ( humic acids and fulvic acids) may migrate into the soil. The presence of large amount of cations in the soil metal such as iron or calcium or even of clay insolubilises the humic acids and fulvic acids and prevents their migration, forming what is called brown soils. In the presence of small amounts of cation metal , the migration of small molecules humic ( fulvic acids ) causes small amounts of metals in surface horizons, forming what are called podzols. The activity of burrowing animals (earthworms, ants, termites) contributes to a rapid contacting compounds with humic mineral matter, thus preventing leaching and thus their loss to the ecosystems or agroecosystems.

Organic matter in decomposition, humus product is comprised of:

• plant fragments ( leaves , needles , stems , roots , wood , bark , seeds , pollen ) decaying
• of exudates and root exudates of plants ( propolis ) and animals ( honeydew ) above the ground,
• of excreta and excreta ( mucus , slime ) of earthworms and other animals and microbial soil
• of dead animals and many microorganisms, fungi and bacteria,

All these elements are constantly being digested, displaced ( bioturbation ) and mobilized by a community of organisms known as detritivores , saprophagous or saprophytes : bacteria , fungi and invertebrates. In cold zone or continental, the formation of humus is accelerated in the spring when the temperature rises and the humidity is high.

Evolution of humus after the contribution of organic materials and nitrogen fertilizer in cultivated soil.

The humus can accumulate and grow very slowly in cold climates, to establish a carbon sink , but in warm climates, it can disappear very quickly and mineralize. It is generally absent from tropical forests , but the man produced locally in the Amazon, from charcoal , an equivalent of humus said Terra preta. Some very specific environments may show significant accumulations of organic matter humified, constituting as much carbon sinks : these bogs in cold climate (mountains, boreal) and huge accumulations observed in the forest on "white sands" in the middle tropical.

Humus is a large pool of organic matter in soil. It is useful for the farmer, gardener or forester to know the total amount of humus and its quality. One clue is the quality of its C / N ratio of soil. Like carbon and nitrogen do not recycle at the same speed (the carbon is then breathed "runs" faster than nitrogen, which is renewed with protein) a C / N Low (10 or less) indicates good soil biological activity, whereas C / N ratio (20 or more) indicates a slowdown in this activity. The smell and the visual and microscopic observation of the component agencies provide information on the quality of humus, well, if any, analysis of its chemical composition. We must also take account of the biochemical nature of carbon compounds, there is a noticeable difference in the kinetics of humification between lignified cellulosic compounds and compounds. It is possible by chemical analysis preceded by a mild acid hydrolysis to determine a C / N hydolysable which provides vital information on the rate of evolution of organic compounds added to or present in the soil so the role of humus terms of productivity and environment.

Humus, the chemical sense, consists of free humus (= humified organic matter, unrelated to clays or metal oxides) and humus bound. Humus is a free light fraction C / N ratio, readily biodegradable (except in very acid soils, or clogged) and easily in the migrant profile in well-drained soils or where the water table drops. During the process of leaching , there is a deep accumulation of non-biodegraded humic compounds, which can form by complexing with metals that migrated level indurated ( alias ). Humus Humus is linked most stable one that is most interesting on a agricultural sustainability and its cation exchange capacity ("CEC") and anionic. It is also called humin insolubilization. These are the migrants humic compounds (humic and fulvic above), soluble or colloidal, that filter water color "tea" in certain tropical or temperate.

Forms of humus

On the slopes, and under good conditions, the humus layer rarely exceeds 30-40 cm. It is thicker in the valleys and hollows.

According to that humus has been formed in an aerated soil or rather suffocating (eg because of a total water saturation or compaction repeated) can be classified into two categories humus.

Humus formed under aerobic conditions:

• The mull , with good incorporation of organic matter and mineral matter carried mainly by earthworms present in the forests to intense biological activity and grasslands. Then we find that debris (leaves) of the previous year or the previous autumn, and a layer of varying thickness of material organo-mineral brown. The soil is rich in nutrients, mineralization is fast: it is an ideal environment for earthworms except where the soil is calcareous (rendzina Black Forest). In tropical areas (savanna) and sub-desert environments, the Mull can be produced by other burrowing organisms such as termites and insects Tenebrionidae ;
• The modern , with a surface layer of organic matter unincorporated, humified the fauna and fungi , found in forests and moors biologically active medium. It shows (fall) leaves of the year who undergo decomposition mainly fungal , but leaves the previous year partly decomposed, reduced to their network of ribs (skeletonized), with many filaments of fungi , roots ( mycorrhizae ) and especially fecal pellets (droppings) from animals in the litter and humus layer (thickness of a few millimeters to several centimeters). Its smell fungus is characteristic ("modern smell");
• The mortality , with a surface layer of organic matter humified with little or no present in forests and heathlands low biological activity, which slows the rate of decomposition of plant debris, resulting in soil acidification and a phenomenon podzolization. The heath is an example of mortality. The thickness of this type of humus can be considerable, but is not a criterion for identification. The portion of Fire is often the means by which this form of humus is its balance and allow vegetation to recover, restoring the soil nutrients immobilized in the organic layer

Humus formed by anaerobic

• The peat , containing a large quantity of identifiable plant residues, sometimes dating back several thousand years. It is a veritable archive of the environment. Peat is formed in environments flooded permanently, in the presence of dense aquatic vegetation and high growth ( Sphagnum , large sedges , manna , etc. ...). The peat contains many pollen that can reconstruct the history of the landscape until very ancient times;
• The anmoor , containing a large amount of humified organic matter mixed with clay. The anmoor forms in temporarily flooded environments, such as along rivers, the drying phase to the biological processes leading to humification to unfold

Complex clay-humic

Clay-humic complexes (or CAH) are formed by the combination of clay and humus, both in the flocculated state following the work of micro-organisms in the soil, and particularly earthworms , which through the bringing together in liquid medium (as in a test tube) can bind these molecules (negatively polarized ) by a cation bivalent : the calcium (Ca + +). It appears that the mucus of some agencies can also play a role in the formation of these complexes become stable and insoluble once dried (like cement when it "takes"), which explains the resistance of humus in water and the erosion and maintaining its structure and its unique capillary action.

These complexes can further fix heavy metals, possibly radioactive, restricting their transfer to plants and water, and the food chain.

Destruction of humus

Effects of soil erosion.

Glazes.

The contributions of biocides , pesticides and fertilizers can degrade or kill the humus.

Tillage kills humus by burying it, causing a too rapid mineralization of organic matter and soil loss that commonly reach 10 tons / year / ha in temperate zones and up to several hundred tons in the tropics.

The loss of humus is also reflected by a phenomenon of glaze tilled soil, which greatly reduces their ability to absorb water. The latter, polluted by pesticides and excess nitrates (officials swarm of algae and green cyanobacteria visible on the ground) runs off, carrying fine particles that increase turbidity in rivers.

Today, there are many methods to grow crops without destroying the humus: Organic farming , cultivation simplified technique , using the RCW fragmented , natural farming , etc..

(1 votes, average: 4.00 out of 5, rated)

 Loading ...

Help us improve the wiki Send Your Comments