Understanding Soil: Composition, Formation, and Uses
Definition and Importance of Soil
Soil can be defined as a geological layer, fragmented and of varying thickness, overlying the Earth’s crust. It results from the mechanical or chemical weathering of preexisting rock.
Land Use and Fragility
Uses:
- Support of vegetation
- Foundation for buildings
- Location of septic tanks
- Source of mineral resources
Fragility:
- Erosion
- Pollution
- Overexploitation
- Impoverishment of fertility
Composition and Structure of Soil
- Inorganic: Includes air (oxygen and CO2), water, and minerals from the weathering of parent rock, which are often fragmented rock and minerals.
- Organic: Composed of organic matter that has not undergone complete decomposition, and various microorganisms forming the humus from a series of partial transformations of organic matter, whose original structure is no longer recognizable.
Porosity and Permeability of Soil
- Porosity is important for soil cultivation, as it defines the volume of water that can be retained, thus giving the soil volume.
- Soil permeability is the property of the porous soil system that allows fluid flow.
Soil Processes
- Identifies the difference between what is soil and what is not.
- Identifying and classifying soil is often the object of our study, resulting in soil taxonomies.
- Requires recognizing the features and properties that distinguish a soil from other natural bodies.
Polygonal Soil
We broadly refer to soils with a macro-structure that holds this type of geometry as polygonal soils. Usually, they are also evident on the surface in beautiful shapes.
Cryosols
Cryosols include soils formed in a permafrost environment. When water is present, it occurs mainly in the form of ice.
Soil Profile
Horizon A: Eluviation Zone
This is the uppermost layer (wash zone). It is also called the leaching or washing horizon because it has few mineral salts, as these are washed away by infiltrating water (along with fine mineral fragments). The roots of most plants are found in this area. Its color is dark because of the abundance of organic matter (humus). Several subhorizons can be distinguished:
- A0: Consists almost exclusively of non-decomposed plant and animal remains.
- A1: Dark, as it is formed by more evolved humus, which forms aggregates with mineral matter, giving the soil its structure and its ability to retain cations (Ca++, K+, NH4+…) preventing their loss by vertical leaching.
- A2: Where mineral matter dominates and washing is more intense.
Horizon B: Illuviation Zone
It is lighter in color due to a lack of humus. Materials from the A horizon are deposited here, mainly colloidal materials (clays, metal oxides and hydroxides, or carbonates…).
Horizon C: Weathered Parent Material
Formed by the parent rock, more or less disjointed and weathered. It is the highest part of the rock material on which the soil lies.
Concept of Bedrock
Rock on which the soil develops and which gives rise to mineral disintegration.
Process of Soil Formation
Soil formation takes place in successive stages that run parallel to the mechanism of ecological succession in the community it supports, maturing at the same time it tends to reach its climax. Stages of soil formation:
- The bedrock begins to disintegrate.
- Organic matter facilitates disintegration.
- Horizons begin to form.
- The soil supports dense vegetation.
Humus
Humus is the more or less stable fraction of soil organic matter, which is formed after most of the vegetable or animal substances added to the soil have decomposed.