Physical and mechanical properties of the soil: 8 indicators and what they mean
The value of the physical and mechanical properties of the soil is important for determining its value for agricultural use. Consider the description of the characteristics of physical and mechanical properties, which include plasticity, stickiness, swelling and its corresponding shrinkage, cohesion, physical maturity of the soil, its hardness and resistivity when processed by agricultural machines.
General concepts
Soil physical and mechanical properties allow it to intensively influence the growth and development of all forms of plants, the speed and friendliness of seed germination, the spread of the root system in depth and width, have a significant impact on tillage machines.
Physical and mechanical properties
This concept includes plasticity, soil stickiness, swelling under the influence of moisture, shrinkage when drying, hardness and resistivity, cohesion, physical ripeness.
Plasticity
The ability of an earthen clod to acquire in its raw state a shape that was artificially given to it. In this case, no cracks should form, the lump should be preserved even after the end of the impact. Too wet or dry soil will not be plastic, good plasticity appears with a certain degree of humidity.
Plasticity with a maximum indicator can be determined using the Vasiliev cone, if it goes 1 cm deep into the soil under the influence of its weight in 5 seconds. The minimum indicator is obtained if a cord with a diameter of 3 mm, which can be rolled out of the ground, breaks into separate parts.
Plasticity indicates the mechanical composition of the soil (0 - sand, 0-7 - characteristic of sandy loam, from 7 to 17 - loam, over 17 - clay). The property depends on the size of the particles, the composition of the absorbed s alts, because they largely show how wet the soil is and how much humus is in it. Humus soil is less plastic.
Stickiness
Property is defined as the ability of wet soil to stick to objects it touches. Stickiness is detected if the adhesion of particles is weaker than between them and objects. The property depends on the chemical, mineral, mechanical composition, humidity and structure. Structureless clay soils stick more strongly, structural and loose soils stick less.
Stickness rises with increasing moisture, but to a certain level, then decreases even for wet soil, as the adhesion between particles increases. In structural soils, this property is found at 60-80% of the total moisture capacity. Structureless earth sticks even with low humidity.
Soil stickiness is measured in the effort that must be expended to tear off an adhering object from the ground (in g per 1 cm2). There are viscous (15g/cm2), strongly (5-15), medium (2-5) and slightly viscous (<2g/cm2) soils.
<2г/см2) почвы.Swelling
This property describes the increase in the volume of land after wetting. As a result, the soil increases in volume. The soil swells, which contains a lot of colloids, most of all swelling is characteristic of clay soils. Soils with vermiculite and similar minerals swell easily.
Swelling is determined in percent by volume. The value depends on the quality and number of colloids. Exchangeable cations influence the swelling. If there are 1-valent cations in the soil (mainly sodium), then the earth is able to swell by 120-150%, when saturated with 2- and 3-valent cations, the soil practically does not swell.
Shrinkage
This concept defines the decrease in the volume of the soil when it dries. Shrinkage is measured as a percentage of the resulting volume of the original. Shrinkage depends on the same conditions as swelling, and is, as it were, its reverse process. With a large shrinkage, the soil cracks, the roots of plants are torn.
Connectedness
The ability of the soil to resist the force that is aimed at separating the soil particles. Connectivity indicates the structural strength of the soil. The property depends on the mineral and mechanical composition, composition of cations, humidity, organic content, structuredness. Expressed in kg/cm2. Considerable connectivity is inherent in clay soils, the level increases if the soil is saturated with sodium ions.
The connectivity of sandy soils increases with an increase in organic matter and decreases under the same conditions in clay soils. Structural lands have a low connectivity, unstructured - more.Soils with high cohesion have good resistance to weathering and water erosion.
Physical ripeness
The condition of the soil when it is easily worked, lumpy and loose. The earth crumbles, does not stick to agricultural machines. Sandy and sandy loamy soil ripens the fastest, clayey soil lasts. The rate of physical ripeness also depends on the humus content, the more it is, the faster the soil becomes suitable for processing.
Hardness
Determined by the resistance of the soil to the penetration of various objects into it. Hardness is expressed in kg/cm2. Defined by characteristics that are inherent in connectivity.
The hardness increases as the humidity level decreases. The presence of calcium and magnesium lowers the hardness by an order of magnitude compared to the hardness of solonetzic soils.Clays and loams are hard, sandy ones are softer. Hardness determines another property - resistivity, which determines the suitability of the land for agricultural cultivation.
According to hardness, soils are divided into loose (100kg/cm2). If the soil is too hard, it indicates poor agrophysical properties.
Resistivity
Expressed by the effort that must be expended on cutting the formation, turning it over and rubbing against the surface of the tool. Measured in the range from 0.2 to 1.2 kg / cm2, it is affected by composition, density, humidity, cation composition, hardness, organic volume, structure.
Small resistance in light, unsaturated s alts, sandy loam and sandy soils, the greatest - in clay and s alt marshes. When cultivating virgin lands and unkempt lands, the resistance increases by 45-50% relative to plowed fields.
Well-structured soils with high humus content have less resistance than those with weak structure and little humus layer.
Physical and mechanical properties of the soil determine its characteristics, which affect the value of the land, primarily for agricultural use. Powerful, structural, high-humus, well-aerated and moderately moist soils of light mechanical composition have the best properties. Among all types of soils, chernozems are considered the best in most indicators. These are the most suitable lands for agricultural use, the most fertile and fruitful.
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