You soil types are the different classes used to distinguish the soils present on the earth's surface according to criteria that vary from country to country. Some of the most common criteria are those inherent to the soil — such as texture, mineral composition, characteristics of the parent rock, depth and porosity — as well as external ones — such as the climate of the soil development area and the relief.
In general terms and according to texture, soils can be classified into:
sandy;
silty;
clayey
Read too:Forms of soil degradation
Summary of soil types
Soils are mineral and organic bodies that cover the earth's surface. They are a direct result of the processes of weathering.
The formation of soils, a process called pedogenesis, depends on factors such as climate, relief and slope of the land, as well as the presence of animal and plant life.
The different types of soils are identified based on criteria such as: texture, mineral composition, aspects of the mother rock, climatic conditions of the formation area, relief and others.
According to texture, soils can be classified as sandy, silty and clayey.
There are also organic soils, formed essentially by organic matter.
The Brazilian Soil Classification System identified 13 soil types in Brazil. The most common are the latosol and the argisol.
What is soil?
soils are mineral and organic bodies formed on the earth's surfacethrough the action of weathering agents on a rocky substrate. This is unconsolidated material that was not transported through erosive processes, thus developing a soil profile in that area. Soil formation is called pedogenesis.
Several factors are involved in soil formation. Are they:
climate elements, which determine the variation in temperatures, moisture content and rainfall of an area;
relief and topography;
presence of biological agents (animals and plants).
The mineral composition of a soil varies according to the nature of the parent rock — nomenclature associated with the rock that has undergone the processes of mechanical and chemical decomposition that originated the soil — and also the presence of microorganisms and small animals responsible for what we call weathering biological.
The ground is dynamic, since its interaction with the environment and, therefore, with the weathering agents is constant. The presence of vegetation cover helps in the maintenance and nutrition of the soil, while its removal makes the substrate even more exposed to the action of rainwater, winds and other elements external.
It is also important to note that, when we observe a soil profile, we identify the presence of several horizons. The horizons are layers superimposed on each other, which were formed through the action of one (or more) weathering process. The colors and composition (mineral and organic) of the horizons are variable, which allows us to classify soils into different types.
What types of soil exist?
The types of soil existing around the world are classified according to various criteria, considering its inherent characteristics — such as mineral composition, texture, porosity, presence or absence of a particular horizon, the thickness of the horizons, the depth—and aspects of their area of formation— like the climate it's the relief.
Based on these and other aspects and the importance given to each of them, the types of soils vary considerably from country to country.|1| Broadly speaking, they fall into one of the categories described below.
sandy soils: have about 70% of materials with median granulometry (0.05 to 2 mm), classified as sand. For this reason, they have high porosity and absorb water more easily. On the other hand, they are chemically and physically poorly fertile, with low organic matter content and high acidity (low pH), in addition to being highly susceptible to erosive processes. common in areas of semi-arid climate.
silty soils: they have an intermediate granulometry between sand and clay, what we call silt (0.002 to 0.05 mm). Although their appearance is similar to clayey soils as they are formed by fine particles, they do not are cohesively aggregated, which means that these soils are quite susceptible to the processes erosive.
Clay soils: at least 30% of the material they are composed of has a very fine texture (< 0.002 mm), classified as clay. They can be formed from several minerals, especially iron and aluminum. They are less porous and have low permeability and, as a result, are able to retain the absorbed water for a longer time. They are well structured and less prone to erosion.
Organic soils: also called humic, they are very rich in organic matter and nutrients coming mainly from rich vegetation that sustains them, but also of the microorganisms and small animals that make them their habitat. Quite common in humid climate regions.
Read too: What is the difference between erosion and weathering?
Types of soil in Brazil
There are at least 13 types of soil in the Brazilian territory. Below we present a brief description of each one of them, following the Brazilian Soil Classification System of Embrapa (Brazilian Agricultural Research Corporation).
Argisols: second most common soil type in Brazil. They are characterized by the presence of clay in their B horizon (layer in which elements are present resulting from weathering, such as clay, oxides and hydroxides of iron and aluminum and also raw material |2|). They have deep and well-developed profiles. Its color varies from yellowish to reddish.
Cambisols: shallow soils still in formation, with a B horizon, which we call incipient. Its color varies from brown to yellowish brown.
Chernosols: nutrient-rich soils due to the presence of large amounts of organic matter in their surface layer, called the A horizon. They may have a well-developed or incipient B horizon, in addition to the presence of other elements, such as calcium and potassium. They have a black color.
Spodosols: sandy textured soils, mostly, and with variable depth. They are characterized by the presence of organic matter in the B horizon and a horizon above it, the E, which is lighter in color and is located just below the surface layer.
Gleissolos: present high water saturation most of the year, being found in areas such as river and coastal plains. Due to the chemical processes triggered by the water in contact with the minerals present in the substrate, its color varies from bluish and greenish to gray tones.
Latosols: are the most common type in Brazil, found in more than 40% of the national territory. They went through a long process of weathering until they reached their current stage, being, therefore, deep and well developed. They have a red or yellowish color and good permeability, but they are not chemically fertile.
Luvisols: they are very shallow and have a high concentration of clay and minerals, such as calcium and magnesium, with very different textures along their length. They tend to have intense leaching on the top layer.
Neosols: incipient soils that do not have an alteration horizon (horizon B), which makes them very shallow. Its characteristics are still very similar to those arranged by the mother rock.
Nitosols: deep and well-developed clayey soils, presenting a reddish color and a shine that receives the name of waxiness, an aspect derived from weathering and also from the displacement of clays within the profile of the ground.
Organosols: composed of a high concentration of organic matter. They have a high saturation index and are very dark in color.
Planosols: low permeability and shallow soils that present a B horizon with a high concentration of clay, in contrast to the A horizon, with a sandy texture.
Plintosols: present a subsurface layer with a high concentration of iron, which results in the formation of nodules called plinthite or even concretions with greater coverage. They are acidic and not very fertile and develop in the presence of high humidity and heat.
Vertisols: clayey soils of low permeability that develop in areas of dry climate. Due to the presence of expansive clay, they change slightly in appearance in the hot and dry season, when cracks appear on their surface.
Grades
|1| TOLEDO, Maria Cristina Motta de; OLIVEIRA, Sonia Maria Barros de; MELFI, Adolpho José. From rock to soil: weathering and pedogenesis. In: TEIXEIRA, Wilson.; FAIRCHILD, Thomas Rich.; TOLEDO, Maria Cristina Motta de; TAIOLI, Fabio. (Eds.) deciphering the earth. São Paulo, SP: Companhia Editora Nacional, 2009, 2nd ed. P. 210-239.
|2| Idem.
image credits
[1] Wagner Santos de Almeida / shutterstock
By Paloma Guitarrara
Geography teacher
Source: Brazil School - https://brasilescola.uol.com.br/geografia/tipos-de-solo.htm