Thanks to the erosion and activity of living beings, the outer portion of the earth's rocky crust, its surface, becomes what we know as "soils."
Without the soil the existence of higher plants would be impossible and, without them, neither we nor the rest of the animals could live.
Although it forms a very thin layer, it is essential for life on dry land. Each region of the planet has soils that characterize it, according to the type of rock from which it has been formed and the agents that have modified it.
The soil comes from the interaction between the atmosphere, and biosphere. It is formed from the decomposition of the mother rock, due to climatic factors and the action of living things. This implies that the soil has a mineral and a biological part, which allows it to support a multitude of plant and animal species.
The decomposition of the mother rock may be due to physical and mechanical factors, or by alteration, or chemical decomposition. In this process, very small elements are formed that make up the soil, colloids and ions. Depending on the percentage of colloids and ions, and their origin, the soil will have certain characteristics.
Organic matter comes mainly from the vegetation that colonizes the mother rock. The decomposition of these contributions forms the gross humus. To these vegetal remains are added those coming from the decomposition of the contributions of the fauna, although in its total proportion it is of minor importance.
The decomposition of organic matter provides different minerals and gases to the soil: ammonia, nitrates, phosphates ... These are essential elements for the metabolism of living beings and make up the trophic soil reserve for plants, in addition to ensuring their stability.
The soil is classified according to its texture: fine or coarse, and by its structure: flocculated, aggregated or dispersed, which defines its porosity that allows a greater or lesser circulation of water, and therefore the existence of vegetables that need more concentrations or less high water or gas.
The soil can also be classified by its chemical characteristics, by its power of absorption of colloids and by its degree of acidity (pH), which allows the existence of a vegetation more or less in need of certain compounds.
The soils not evolved They are raw soils, very close to the mother rock and have hardly any contribution of organic matter. They are the result of erosive phenomena or the recent accumulation of alluvial contributions. Of this type are polar soils and deserts, both rock and sand, as well as beaches.
The soils little evolved They depend largely on the nature of the mother rock. There are three basic types: ranker, rendzina and steppe soils. Ránker soils are more or less acidic, such as tundra and alpine soils. The rendzina soils are formed on a carbonated mother rock, such as limestone, are usually the result of erosion and are basic soils. The steppe soils develop in continental climates and sub-arid Mediterranean. The contribution of organic matter is very high. Depending on the aridity of the climate they can be from chestnut to red.
In the evolved soils We found all kinds of humus, and some independence from the mother rock. There is a great variety and among them are the soils of temperate forests, those of regions with great abundance of rainfall, those of temperate climates and the Mediterranean red soil. In general, if the climate is favorable and the place is accessible, most of these soils are now occupied by agricultural holdings.
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