He Soil forms With the weathering of the rocks. This material is composed of mineral particles and organic materials, among others.
Air, water and living organisms are also part of the thin layer of material that covers the surface of the earth. All the elements present in it are in a slow but constant interaction with each other.
Most plants get their nutrients from the soil and are the main source of food for humans and animals. Thus, much of the biota depends on the soil for its existence.
How is the soil formed?
Soil profile
The profile of a soil is defined as the chemical and physical description of the horizons that make up the soil, from the surface to the depth, where the processes of soil formation are no longer evident.
Horizons in a profile have been formed and differentiated from the original parent material in place. These are not the result of geological processes, although some characteristics of a profile may be the result of Geological events . Most soils exhibit the following horizons:
Horizon O
It includes a layer of debris and sometimes a humus. These materials are differentiated by the degree of decomposition of the organic matter. This horizon is generally not present in soils of cultivation, in maintained meadows and soils severely eroded.
Horizon A
Mulch rich in humus where nutrients, organic matter and biological activity are greater. The A horizon is usually darker than other horizons due to organic materials.
Horizon E
This horizon is mostly devoid of clays in its composition and sometimes coloring agents, so it is much clearer than other horizons.
Horizon B
Subsoil rich in clays. This horizon is usually less fertile than the mulch, but maintains a higher humidity. It generally has a lighter color and less biological activity than the A horizon. The texture may be much heavier than that of A as well.
Horizon C
It is composed of little meteorized rocks that are located in the bottom and is the source from which the horizons A and B are formed.
Composition of the soil
There are only four categories of the infinite variety of substances that can be found in soils: minerals, organic matter, air and water.
The ratio in which these four components are found can vary greatly. The air and water present are found in the porosities between the solid particles of the soil.
The radius between pores that are filled with water from those that are filled with air can vary between seasons, weekly or even daily.
This depends on the additions of water corresponding to rainfall, flow, groundwater discharge and avalanches. Therefore, the volume of the pore space itself can be altered by certain processes.
Floor orders
The soil taxonomy at its highest hierarchy level identifies 12 soil orders. The names of the orders and the taxonomic properties of the mimes have Greek and Latin roots that reveal something about the material.
It is also recognized 6 suborders that are in the next level of classification. There are about 300 groups and more than 2,400 subgroups of soils.
Soils within a subgroup that have similar physical and chemical properties that affect their response to handling and manipulation are recognized as families. The series are the lowest category in the soil classification system.
When making maps of a soil, the researchers look for areas with soil-forming factors that are similar and thus find soils of similar composition.
These mappings describe features such as colors, texture and structure. These are the ones that will allow to classify to a certain portion of ground within a certain taxonomic category.
Factors affecting soil formation
1- Weathering
The soil is formed continuously but slowly, from the gradual degradation of rocks through weathering.
- Physical weather : Degradation of rocks from the result of the mechanical action. Changes in temperature, abrasion or freezing are all causes that give rise to this process.
- Chemical weathering : Degradation of rocks through change in chemical composition. This can occur when the minerals inside the rocks react with water, air or other reagents.
- Biological weathering : Degradation of rocks thanks to living elements. Animal excavators cause water and air to enter the rock. In the same way the roots of the plants can grow through the cracks, causing them to break.
2- Accumulation of material
The accumulation of material through the action of water, wind and gravity also contributes to the formation of the soil. This process can become very slow, taking several tens of thousands of years. Five major interactions are those that affect soil formation:
- Parental material: minerals that form the base of the soil.
- Living organisms: influence the formation of soil.
- Climate: affects the rate of weathering and organic decomposition.
- Topography: slope inclination influences factors such as irrigation, erosion and deposition.
- Time: influence on soil properties.
Interactions between these factors produce an infinite variety of soil types across the entire land surface.
Parenting Materials
They are defined as the soil minerals that form the base of the same. They are produced from rocks that have undergone processes of weathering and natural erosion.
Water, wind, changes in temperature, gravity, chemical interaction, living organisms and differences in pressure help the rupture of the parent material.
The types of parent materials and the conditions under which they are broken will influence the properties of the soil they form.
Organisms
Soil formation is influenced by organisms, microorganisms, digging insects, animals and humans. As the soil forms the plants begin to grow on it. Plants mature, die and new take their place, the leaves and roots then become part of the soil.
Bacteria, fungi, worms and other excavators degrade the litter, debris and animal waste that eventually become part of the soil as well. This material can take the form of peat, humus or charcoal.
Weather
Temperature affects the rate at which weathering and organic decomposition occur. With cooler and drier conditions, these processes can be slow and with hot and humid conditions, they can become relatively fast.
The rain dissolves some of the soil materials and holds in suspension some others. The water carries or filters these materials through the soil. Over time this process can change the soil and make it less fertile.
Topography
The shape, length and degree of slopes affect drainage processes. The aspect of a slope determines the type of vegetation and indicates the amount of rainwater it has received.
Soil materials are progressively moved within the natural landscape by the action of water, gravity and wind. In this way, the soils present on steep slopes tend to be much thinner. In this way, the types of soils that are transported include:
- Alluvial: Those transported by rain.
- Coluviales: Those transported by gravity.
- Wind: Those transported by the wind.
Weather
Soil properties can vary according to how long the soil has been exposed to erosion.
Materials that have recently been deposited as those of an avalanche show no sign of developmental activities. Rock minerals undergo more weathering processes and thus form materials such as clays and iron and aluminum oxides.
Stages in soil formation
All soil-forming activity begins with the accumulation of parent material. This step is followed by the accumulation of organic material on the surface.
Some pioneering species such as grasses and algae live and die on this surface, and organic material begins to accumulate on both the surface and the interior where the roots were found.
The A horizon begins to form once sufficient organic material has been transformed by the soil biota into humic materials.
The humic materials stain the soil particles making them brown or black. This portion will continue to grow in thickness until the rate of addition of organic material equals that of erosion losses. This state will be affected by certain environmental conditions such as climate changes and vegetation succession.
The B horizon begins to form as materials are brought to depth by the water being filtered. These materials include humic substances, clays, salts and metals. The E horizon is formed as the B horizon moves deeper into the ground.
References
- Queensland Government. How soils form. [Online] March 14, 2016. [Quoted on: February 27, 2017.] qld.gov.au/environment.
- Scharf, R. CHARACTERIZATION OF THE ASHEPOO-COMBAHEE-EDISTO (ACE) BASIN, SOUTH CAROLINA. [Online] [Quoted on: February 27, 2017.] webapp1.
- United States Department of Agriculture.Soil Formation and Classification. [Online] [Quoted on: February 27, 2017.] nrcs.usda.gov.
- Soil-net.com. Soil Formation - Introduction. [Online] [Quoted on: February 27, 2017.] soil-net.com.
- The-compost-gardener.com. What is Soil? [Online] [Quote On: February 27, 2017.] the-compost-gardener.com.