There are many types of soils and each of them has striking differences from other varieties. The soil consists of a variety of particles of any size, which are called "mechanical elements". The content of these components allows you to determine the granulometric composition of the soil, which is expressed as a percentage of the mass of dry earth. Mechanical elements, in turn, are grouped in size and form fractions.
Common fractions of soil constituents
There are several groups of mechanical composition, but the following is considered the most common classification:
- sand - is divided into large, medium and small;
- silt - is divided into rough, thin and colloids;
- dust - coarse, medium and fine.
Another division of the granulometric composition of the earth is as follows: loose sand, cohesive sand, light loam, medium and heavy, sandy loam, light clay, medium and heavy. Each group contains a certain percentage of physical clay.
The soil is constantly changing, as a result of this process, the granulometric composition of soils also does not remain the same (for example, due to podzol formation, sludge is transferred from upper horizons to lower). The structure and porosity of the earth, its heat capacity and coherence, air permeability and moisture capacity depend on the components of the soil.
Skeleton classification of soils (according to N.A. Kachinsky)
|Boundary values, mm||Faction Name|
|more than 3||Rocky soil|
Features of fractions of mechanical elements
One of the main groups forming the granulometric composition of the earth is “stones”. It represents fragments of primary minerals, has poor water permeability and a fairly minimal moisture capacity. Plants growing in this land do not receive sufficient nutrients.
The second most important component is sand - these are fragments of minerals, in which quartz and feldspars occupy the largest part. This type of fractions can be characterized as well permeable with low water lifting capacity; moisture capacity is not more than 3-10%.
The sludge fraction contains a small amount of minerals that make up the solid phase of soils and is mainly formed from humic substances and secondary elements. It can coagulate, is a source of plant life and is rich in aluminum and iron oxides. The mechanical composition is water-absorbing, water permeability is minimal.
Coarse dust belongs to the sand fraction, but has good water properties and does not take part in soil formation. Moreover, after rains, as a result of drying, a crust appears on the surface of the earth, which negatively affects the water-air properties of the layers. Due to this feature, some plants may die. Medium and fine dust has low liquid permeability and high moisture capacity; she is not involved in the formation of soil.
The granulometric composition of soils contains large particles (more than 1 mm) - these are stones and gravel, which form the skeletal part and small (less than 1 mm) - fine earth. Each fraction has unique properties and features. Soil fertility depends on a balanced number of composition elements.
The important role of the mechanical composition of the earth
The mechanical composition of the soil is one of the most important indicators that agronomists should be guided by. It is he who determines the fertility of the soil. The more mechanical fractions in the granular composition of the soil, the better, richer and in large quantities contains a variety of mineral elements necessary for the full development of plants and their nutrition. This feature affects the processes of structure formation.