Soil is the fundamental system that sustains life on Earth. The soil includes both the geological part and the biological communities that live in it and that contribute to its formation and transformation. The discipline in charge of studying, evaluating, comparing and determining the composition of soils is edaphology . Soils are classified according to their composition and structure.
In AgroCorrn we are going to talk about the types of soils and their main characteristics and thus better understand the soil we walk on.
What is soil
Soil is a porous, biologically active, structured medium that is developed on the Earth’s surface . Soil includes those biologically active surface materials of the geosphere (solid part of the planet). It differs from rocks in that it includes inorganic (mineral, water, gases) and organic (humus) matter that are being transformed, which leads to its structuring and organization in horizons.
It has a very important role as it fulfills important ecological functions , it is the habitat of many living beings, it regulates the hydrological cycle and the climate, and it participates in biogeochemical recycling (such as the carbon and nitrogen cycle, etc.).
Therefore, we must be aware of the pollution that we produce, which affects all living beings on the planet. In AgroCorrn we have prepared this other article on How to avoid soil contamination .
How the floor is divided and organized
Soils and their characteristics can vary spatially, both laterally and vertically. Vertical variability is defined by the presence of different levels with different characteristics and properties, forming a sequence of horizons that constitutes the edaphic profile or solum .
Therefore, horizons are levels more or less parallel to the surface with characteristics that differentiate it from the others but are related.
The soil begins to form when a rock is exposed to the atmosphere, and begins to be colonized by lichens and when its minerals begin to decompose and alter physically and chemically. This process is known as meterorization . This results in the formation of horizons A and C.
- Horizon A: it is the most superficial horizon and is formed by biological activity as a consequence of the implantation of vegetation.
- Horizon B: also called the accumulation horizon. Its origin is a consequence of the processes of translocation and transformation of the materials of horizons A and B. In it, products of alteration and new formation accumulate.
- Horizon C: it is the deepest (located after B) and is made up of bedrock and fragments derived from weathering.
Types of soils and their characteristics
There are several systems of soil classification (Kubiena Classification, French, Soil taxonomy-USDA, WRB-FAO / UNESCO), but recently, in 2006 the FAO, the ISRIC / World Soil Information and the International Union of Soil Sciences developed a new version of the World Soils Reference Base (WBR). Currently, it is the official soil classification system in the European Union and establishes the following types of soils :
- Histosols : made up of little or no decomposed vegetable remains, with or without a mixture of sand, silt or clay, in conditions of excess water. They typically appear in mobs or bogs.
Soils conditioned by anthropic influences
- Anthrosols : formed by land mobilization, accumulation of rubble, residual sludge or contributions of manure or with agricultural use.
- Technosols: soils developed on manufacturing, construction or mining waste.
Low evolution soils highly conditioned by climate
- Cryosols : they are permanently frozen (permafrost).
Low evolution soils highly conditioned by the original material
- Andosols : with a high content of amorphous or low crystallinity materials from pyroclastic volcanic materials. They are found in almost any climate.
- Arenosols: sandy soils.
- Vertisols: very clay soils.
Other soils of moderate evolution
- Umbrisols: soils rich in organic matter and acids.
- Cambisols: characterized by weathering of the parent or initial material.
Soils conditioned by topography and water
- Leptosols: they are very shallow soils on continuous rock and extremely gravelly and / or stony soils ( lithosols ).
- Regosols: they are very weakly developed mineral soils.
- Fluvisols: they are located near rivers and present a stratified profile where the amount of organic matter decreases irregularly or is abundant in very deep areas.
- Gleysols: soils with water permanently (or almost) in the first 50 cm. There is a reduction in iron oxides and they can have reddish, brownish or yellowish or grayish / bluish colors.
- Stagnosols: are soils with a layer of water that allow intense reduction conditions and due to the washing of the materials produced by the water, they can present albic or whitish horizons.
- Planosols: these are soils with a light colored surface horizon that shows signs of periodic stagnation of water that abruptly passes to a horizon with a significant increase in clay with respect to the surface horizon.
Soils typically of arid or semi-arid climate
- Solonchaks : soils with a high content of soluble salts (halite, gypsum) and humus.
- Solonetz: rare and have high proportions of sodium and / or magnesium.
- Calcisols: soils with accumulations of calcium carbonate.
- Gypsisols : soils with accumulations of gypsum.
- Durisols: soils with silica.
Typically steppe soils
- Chernozems: cold steppe environments. Surface horizon dark brown or black due to the accumulation of organic matter and may have calcium carbonate in the deeper horizons.
- Kastanozems: drier and warmer steppe environments. Surface horizon of brown color because there is less accumulation of organic matter.
- Phaeozems: warmer and more humid steppe environments. Similar to the previous ones, but without calcium carbonate.
Soils with a clay-rich subsoil
- Albeluvisols: it presents horizons with mineral depletion due to its eluvation by the passage of water.
- Alisols : very acidic soils. In any climate excluding tropical and subtropical climates.
- Acrisols : advanced degree of weathering. Only in tropical and subtropical climates.
- Luvisols and lixisols . They are similar, although they differ in the type of clays they present.
Typically tropical and subtropical climate soils
- Nitisols: deep, well-drained, red tropical soils with a silty subsurface horizon with sodium. Rich in iron.
- Ferralsols : they are the classic soils of the humid tropics, deeply weathered and with red or yellow colors. They are usually clayey with a high content of iron and aluminum compounds.
- Plinthosols: soils with hardened clay, iron and quartz crusts.
S typically uelos cold and humid climate
- Podzols: they have a characteristic B horizon called spodic and it is composed of organic matter, aluminum and iron.
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