What is the ground?

We explain what the soil is and how it is composed. In addition, classification of soils and their different characteristics.

1. What is the ground?

Commonly we call soil the most superficial portion of the earth’s crust , consisting mostly of rock residues from erosive processes and other physical and chemical alterations, as well as organic matter resulting from the biological activity that develops on the surface.

The soil is the most visible portion of the planet, where we sow crops, build our houses and bury our dead. It is an extremely varied and multiform surface , on which climatic phenomena such as rain, wind, etc. occur.

Similarly, the soil is the scene of complex chemical and physical processes , as well as an underground ecosystem of small animals and abundant microorganisms, whose presence directly impacts the fertility of the same.

The soils are formed by the destruction of the rock and the accumulation of different materials over the centuries, in a process that involves numerous physical, chemical and biological variants, which results in an arrangement in well-differentiated layers, such as a cake, observable at the points of failure or fracture of the earth’s crust.

2. How is the soil composed?

The soil is composed of solid, liquid and gaseous ingredients, such as:

• Solid . The mineral skeleton of the soil is mainly composed of rocks, such as silicates (micas, quartz, feldspar), iron oxides (limonite, goetite) and aluminum (gibbsite, boehmite), carbonates (calcite, dolomite), sulfates (aljez), chlorides, nitrates and solids of organic or organic-mineral origin, such as different types of humus.
• Liquids . Water aboundsin the soil, but not always in a pure state (as in deposits) but loaded with ions and salts and various organic substances. Water in the soil travels by capillarity, depending on the permeability of the soil, and transports numerous substances from one level to another.
• Gaseous . The soil has several atmospheric gases such as oxygen (O ₂ ) and carbon dioxide ( CO ₂ ), but depending on the nature of the soil it can also have the presence of gaseous hydrocarbons such as methane (CH ₄ ) and nitrous oxide (N ₂ OR). Soil gases are tremendously varied.

3. Soil characteristics

The properties and characteristics of the soil are enormously varied, according to the type of soil and the particular history of the region where it is located. But in broad strokes we can identify the following characteristics:

• Variability . The soils generally have slightly homogeneous components in their size and constitution, so despite showing themselves as a homogeneous mixture , they actually have rocks and elements of different sizes and different nature.
• Fertility . The possibility of soils to house nutrients derived from nitrogen, sulfur and other elements of importance for plant life, is called fertility and is related to the presence of water and organic matter, and to the porosity of the soil.
• Mutability . Although the processes of soil change are long term and we cannot verify them directly, it is true that they are in constant physical and chemical mutation .
• Robustness . The soils have different physical properties , including solidity and texture: there are some more compact and rigid, others more malleable and soft, depending on their particular geological history.

4. Types of soils

There are different types of soil, each fruit of different formation processes, the result of sedimentation, wind deposition, weathering and organic waste. They can be classified according to two different criteria, which are:

According to its structure . Can we talk about:

• Sandy soils . Unable to retain water, they are scarce in organic matter and therefore not very fertile.
• Limestone soils . They abound in calcareous minerals and therefore in salts, which gives them hardness, aridity and whitish color.
• Humid soils . Of black earth, in them the organic matter abounds in decomposition and they retain the water very well, being very fertile.
• Clayey soils . Composed of fine yellowish grains that retain water very well, so they usually flood easily.
• Stony soils . Composed of rocks of different sizes, they are very porous and do not retain water at all.
• Mixed soils . Mixed soils, usually between sandy and clayey.

According to their physical characteristics . Can we talk about:

• Lithosols . Thin layers of soil up to 10cm deep, with very low vegetation and also called “leptosols”.
• Cambisoles . Young soils with initial accumulation of clays.
• Luvisols . Clay soils with a base saturation of 50% or higher.
• Acrisols . Another type of clay soil, with base saturation less than 50%.
• Gleysols . Floors of constant or almost constant water presence.
• Fluvisols . Young soils of river deposits, usually rich in calcium.
• Rendzina . Soils rich in organic matter on limestone.
• Vertisols . Clay and black soils, located near runoff and rocky slopes.