The soil is an essential natural resource for life and for the production of other resources.Soil science as a science was formed in the XIX century. The founder of the scientific soil science was the outstanding Russian scientist Vasily Vasilyevich Dokuchaev (1846-1903), who defined the soil as “daytime – or close to them horizons of rocks (no matter what), which were more or less naturally modified by the mutual influence of water, air and various kinds organisms – living and dead, which affects in a known manner on the composition, structure and color of such formations. Where this condition is not present, there are no natural soils either, but there is either an artificial mixture or rock. ” By this he emphasized the peculiarity of the soil as an independent natural body, formed as a result of a change in the upper part of the earth’s crust under the influence of the above factors.
Academician V.R. Williams (1863 – 1939) developed the biological theory of soil and its fertility and specified the definition of soil as “a loose surface horizon of the Earth’s land capable of producing crops”. With this he emphasized the most important property of the soil, inherent only to her, her fertility.
The soil is the main and indispensable means of agricultural production, the wealth of any country, as it provides human food, livestock – feed, and industry – raw materials. Agriculture is entirely built on the use of the soil, therefore knowledge of its origin, composition, properties, distribution and ways to increase fertility is a necessary condition for increasing the level of agricultural production.
The soil as a surface layer is composed of 4 essential elements :
- mineral matter : it is the inorganic material composed of rocky and mineral fragments. The most important particles are: clay, silt, gravel and clay.
- Organic matter : it is the accumulation of waste from plants and animals along with the humus (final product of the decomposition of organic waste).
- water : it is retained considering the porosity of the soil, that is, its permeability. Water also determines the solution of the soil or the greater or lesser concentration of salts in the soil.
- air : it is found in the pores of the soil and is characterized by being more humid, with a higher concentration of carbon dioxide and less oxygen than the air in the atmosphere.
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
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 soil change processes 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.
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