Soil fractions
Soil fractions refer to the categorization of soil particles based on their size. This classification is utilized in soil science to determine the granulometric composition of the soil, which is critical for various properties, including water retention capacity, permeability, and nutrient binding capability.
Stones – they are slightly altered rock fragments with a composition nearly identical to the parent rock. Being larger than 20 mm, they are typically excluded from standard grain size analysis of arable soils, though they can be significant in rocky or gravelly soils.
Gravel – smaller stones, 1-20 mm in size. Larger mineral particles do not significantly contribute to most soil processes but influence the soil's structure and water conductivity.
Sand – here we include particles of 0.1-1 mm in size, primarily consisting of chemically inactive silica. Coarse-grained fraction of soil. Soils rich in sand are well-aerated but have a low capacity to retain water and nutrients.
Dust – also composed of silicon compounds, but with finer particles of 0.02-0.1 mm. Medium-grained soil fraction. Soils rich in dust have a better water retention capacity than sandy soils but are more susceptible to water and wind erosion.
Silt – clay particles are the smallest soil particles composed of aluminosilicates, also known as floatable parts, with a particle size less than 0.02 mm. This fine-grained soil fraction exhibits excellent water and nutrient retention capabilities, though it can be challenging to work with and is less permeable.

Determining the content of individual fractions in the soil enables its classification as sandy, clayey, silty, etc., which subsequently influences its physical, chemical, and biological properties, as well as its utilization methods.

Categories and groups of soils
We categorize soil into very light, light, medium, heavy, and very heavy. Within these categories, we identify groups and subgroups based on the percentage of sand, dust, and silt present. In agricultural practice, knowing whether our soil is light or medium is sufficient to select the appropriate agricultural technology, including cultivation machines.

Here is an approximate classification of soils based on their granulometric composition.
Very light (sandy) soil:
- contains more than 85% sand
- well-ventilated, dries quickly
- poor ability to retain water and nutrients
Light soil:
- contains 70-85% sand
- better ability to retain water than very light soil, but still poor
- heats up quickly in the sun
Medium soil (sandy loam, loamy sand):
- a balanced mixture of sand, silt, and dust; no single fraction predominates
- good capacity for retaining water and nutrients
- moderate permeability
Heavy soil (clay):
- contains 35-60% silt
- excellent ability to retain water and nutrients
- poorly permeable, difficult to work with, especially when wet
Very heavy soil (silt):
- contains over 60% silt
- superior ability to retain water and nutrients
- risk of water stagnation, difficult to work with

An example of soil determination based on the content of individual fractions
Quantitative determination of individual fractions is conducted, for instance, by a chemical-agricultural station. The lower the silt and dust fractions, the lighter the soil. For example, if the soil contains 56% sand, 30% dust, and 14% silt, it is classified within the agronomic group of ordinary clay. Consequently, it is considered heavy soil (refer to the diagram "Feret's triangle").

Here are key areas where grain size distribution affects soil tillage practices:
Water retention:
- sandy soils have poor water retention capacity, making them susceptible to drought. They require frequent irrigation, and the risk of waterlogging is low.
- clay soils retain significant water, which can be beneficial in dry conditions, but can also lead to waterlogging and a threat to plant roots in the event of excessive moisture.

Aeration:
- sandy soils are well-aerated, promoting root gas exchange.
- silt soils can be less aerated, increasing the risk of root diseases and improper gas exchange.

Soil treatment:
- sandy soils are manageable irrespective of moisture levels.
- silt soils pose challenges, particularly when wet, and can harden significantly when dry.

Nutrient availability:
- sandy soils necessitate more frequent fertilization due to rapid nutrient loss.
- clay soils retain nutrients more effectively but may bind them, making them less accessible to plants.

Soil temperature:
- sandy soils warm up more quickly in spring, benefiting early crops.
- clay soils warm more slowly, potentially delaying spring planting and germination.

Erosion:
- sandy soils are less susceptible to water erosion than medium or clay soils but can be more vulnerable to wind erosion.
- clay soils are more prone to water erosion, particularly when lacking cover vegetation.

The granulometric composition of the soil, defining the content of individual mineral fractions, is crucial for crop cultivation and the selection of appropriate agricultural machinery. Understanding the granulometric composition of the soil in a given area allows the farmer to adjust cultivation practices to maximize yields and protect the soil. This includes decisions regarding irrigation, soil cultivation, fertilization, crop selection, and other agrotechnical practices.

Terminology
Parent rock – the outer layer of the Earth's crust, which, under the influence of the soil-forming process, produces the mineral material of the soil.
Friable particles - are a granulometric fraction of soil mineral grains, including particles with a diameter of less than 0.02 mm (0.01 mm).