Soil is a complex physical-biological system. It is the means of support and plant nutrition, it is the basis of agricultural production, the natural filter and the protective layer of underground water reserves, as well as the living space of a large amount of organisms. Contains granules of various sizes. Its mechanical properties depend on its texture and structure.The mechanical structure of the soil defined by the volume occupied by the solid components, organic and inorganic, and of the spaces containing gas and a dilute aqueous solution of inorganics, mainly salts.

The distribution in volume of these components is approximately:
• 45% inorganic solid components
• 5% organic solid components
• 50% gases and aqueous solution

The inorganic components of soil depending on their size are classified in:
• Chippers (> 2 mm)
• Sand (2-0,02 mm)
• Sludge (0,02-0,002 mm)
• Clay (<0,002 mm)

The soils are classified into 12 categories granulated, depending on the percentage of sand, clay, silt in the soil. These 12 classes soils occupy a certain position and place in an isosceles triangle called triangle of mechanical soil texture.

Τρίγωνο Μηχανικής Σύστασης Εδάφους

Triangle of mechanical soil texture

The three main categories of soils are sandy or light soils, loam or loamy texture and clay or heavy soils with properties similar of the percentages of sand, clay and silt containing.

The term” structure” of soil includes the form of agglomerates and their distribution in size classes. From the physicochemical point of view, clay is the” active” part of the soil.

The soil pH is the measure of the soil’s acidity or alkalinity. Soil pH is considered a main variable in soils as it controls many chemical processes that take place. It specifically affects the plants’ nutrient availability by controlling the chemical forms of the nutrient. The pH value indicates the kind of nutrients existing in the soil.

pH = 7 neutral soil

pH < 7 acid soil

pH > 7 alkaline soil


The factors affecting the pH value of the soil are the source materials that formed the soil and the rainwater passes through soil which contributes to the leaching of essential nutrients. Many plant diseases are caused or aggravated by extreme pH values. This is because the extreme pH values ​​render the essential nutrients unavailable to plants, or because the soil itself is not healthy.
Soil is not a renewable resource since its formation processes require hundreds or thousands of years .

Human interventions such as land clearing, intensive crops, overexploitation of groundwater, etc. create serious disturbances in soils These disorders usually appear in the form of environmental problems of soil erosion, desertification, salinisation and pollution and result in the degradation or permanent loss of land.
Soil protection from environmental problems can be achieved by adopting appropriate techniques based on maintaining the sustainability of soil resources.

Soil’s main nutrients:

K: Potassium
P: Phosphorus
B: Boron
N: Nitrogen
S: Sulfur
Cu: Copper
Zn: Zinc
Ca: Calcium
Mg: Magnesium
Mo: Molybdenum
Fe: Iron – Ferrum
Mn: Manganese