Soil-structure interface

Introduction

The structure of the soil is its state, which results from the granulometry of the elements that compose it and the way in which they are arranged. The natural evolution of the soil produces a stratified vertical structure (not in the sense of stratification in ecology) which is known as a profile.[1][2]Primary particles (sand, silt or clay) are not found isolated in soils, but forming secondary particles or aggregates.[3].

The layers that are observed are called horizons and their differentiation is due to both their internal dynamics and vertical transport.

Vertical transport has two dimensions with different influences depending on the soil:

- Leaching or washing is produced by water that infiltrates and penetrates vertically from the surface, dragging substances that are deposited mainly by adsorption.

- The other dimension is the vertical rise by capillarity, important especially in climates where wet seasons alternate with dry seasons.

The rock that provides its mineral matrix to the soil is called parent rock. Native soils are distinguished, which sit on their bedrock and represent the most common situation.

Soil profile and horizons

The soil profile is the vertical arrangement of all its horizons or layers. A soil horizon is a horizontal stratum that develops within the soil and has different characteristics of composition, texture, adhesion, etc. . Classically, in complete or evolved soils, three fundamental horizons or layers are distinguished, which constitute their profile and which from the surface downwards are:

• - O horizon, or superficial layer of the A horizon: It is the most superficial part of the soil, formed by leaves, branches and plant remains (detritus).

• - Horizon A, or vertical wash zone: It is the most superficial and herbaceous vegetation takes root there. Its color is generally dark due to the abundance of decomposed organic matter or elaborate humus, determining the passage of water dragging it downwards, fine-sized fragments and soluble compounds. It is subject to bioturbation.

• - or precipitate zone: It practically lacks humus, so its color is lighter (brown or red), in it the materials dragged from above are deposited, mainly clay materials, metallic oxides and hydroxides, etc., situated at this level we will find arid calcareous and tropical lateritic shells.

Soil-structure interface

Introduction

The layers that are observed are called horizons and their differentiation is due to both their internal dynamics and vertical transport.

Vertical transport has two dimensions with different influences depending on the soil:

- Leaching or washing is produced by water that infiltrates and penetrates vertically from the surface, dragging substances that are deposited mainly by adsorption.

- The other dimension is the vertical rise by capillarity, important especially in climates where wet seasons alternate with dry seasons.

The rock that provides its mineral matrix to the soil is called parent rock. Native soils are distinguished, which sit on their bedrock and represent the most common situation.

Soil profile and horizons

• - O horizon, or superficial layer of the A horizon: It is the most superficial part of the soil, formed by leaves, branches and plant remains (detritus).

soil molecular structure

The way in which the earthy particles are arranged together determines the structure of the soil. Clay particles have a lamellar shape and when deposited, they tend to be placed touching the edges or the face of one sheet and the edge of the other. This occurs due to the negative charge on the faces, which also gives rise to the double layer phenomenon. The result of this is the well-known "flocculated structure".

If the negative charges are compensated (as occurs in marine deposits), we will obtain a much more compact "dispersed" structure as the adjacent faces can be brought into contact.

If there are organic colloids in the clay complex, the flocculate derived from these presents the mineral particles distanced from each other by the organic molecules, which, being of notable dimensions, cause the formation of large empty spaces that give the soil a lacunar-type structure. The flocculate can therefore be made up of granules and more or less complex clumps, that is, agglomerates of more or less large diameters that give rise to a granular or clump-type structure quite rich in empty spaces between the contact areas between the agglomerates themselves.

According to recent studies (1965), these agglomerates would be consolidated by lignin, produced by the decomposition of organic substances, which would give a certain stability to the lumps and a certain degree of resistance against disintegrating agents.

Soil structure is a property that is continually changing, depending on a complex of physical, chemical and biological factors.

We can summarize it as: rocky, sandy, silty, clayey, loamy and humiferous.

As agents or factors that favor a good structure of the clumps, from the point of view of agronomic use of the soil, we can remember:

• - Land tillage operations that introduce organic substances, or the formation of empty spaces;

• - The mechanical action exerted by the roots of plants;

• - Climatic variation, variation between ice and thaw, or between dry periods and wet periods;

• - The chemical and coagulant actions of certain ions such as calcium, iron oxide, etc.

Some factors, on the other hand, tend to destroy the above-mentioned lump structure.

• - Water from rain or irrigation can act as a disintegrating agent, due to its mechanical action, or as a diluent of soluble mineral salts;

• - Some cations such as Na act as structure destroyers in alkaline soil, due to their destructive effect on colloids.

The molecular structure of the soil has a very important role in the hydrodynamic behavior of the cultivated soil.

soil molecular structure

If the negative charges are compensated (as occurs in marine deposits), we will obtain a much more compact "dispersed" structure as the adjacent faces can be brought into contact.

Soil structure is a property that is continually changing, depending on a complex of physical, chemical and biological factors.

We can summarize it as: rocky, sandy, silty, clayey, loamy and humiferous.

As agents or factors that favor a good structure of the clumps, from the point of view of agronomic use of the soil, we can remember:

• - Land tillage operations that introduce organic substances, or the formation of empty spaces;

• - The mechanical action exerted by the roots of plants;

• - Climatic variation, variation between ice and thaw, or between dry periods and wet periods;

• - The chemical and coagulant actions of certain ions such as calcium, iron oxide, etc.

Some factors, on the other hand, tend to destroy the above-mentioned lump structure.

• - Water from rain or irrigation can act as a disintegrating agent, due to its mechanical action, or as a diluent of soluble mineral salts;

• - Some cations such as Na act as structure destroyers in alkaline soil, due to their destructive effect on colloids.

The molecular structure of the soil has a very important role in the hydrodynamic behavior of the cultivated soil.

Navegación

Soil-structure interface

Introduction

Soil profile and horizons

Soil-structure interface

Introduction

Soil profile and horizons

soil molecular structure

References

soil molecular structure

References