RUDN University biologist presented a theoretical justification for the analysis of soil quality. The theory is based on thermodynamic analysis and can help to calculate the crucial practical parameters, for example, the optimal moisture content or mechanical tillage. The results are published in Agronomy.

Newswise — Most of the ecological and technological functions of the soil are related to the moisture content in it. What humidity will be optimal for plants in sand and clay? At what humidity should mechanical treatment be carried out for different soils? When will the soil have the maximum microbiological activity for the decomposition of organic residues and the release of carbon dioxide? How should the soil be watered in order to save water resources and prevent secondary salinization of the land? All these practically important tasks have a scientifically based solution within the thermodynamic concept of water retention and physical quality of soils.

Its basic indicator is the water retention curve (WRC), which connects the work on extracting water from the soil (thermodynamic potential of soil moisture) with its quantity (humidity). This dependence is unique for each soil and its shape, as a kind of ID, reflects the physical quality of the soil. Professor Andrey Smagin, an employee of Center for Mathematical Modeling and Design of Sustainable Ecosystems of the RUDN University, Doctor of Biological Sciences, developing a thermodynamic concept of the physical quality of soils, proposed to combine the forces of centrifugal and gravitational fields to remove water from the soil and calculate the thermodynamic potential of soil moisture by simple laboratory experiments with centrifugation of wet soil samples.

Having obtained a representative (more than 400 samples) database of the main genetic types of Eurasian soils of different texture classes from sands to heavy loams and clays, he conducted a rigorous mathematical analysis of the physical forces and mechanisms responsible for the interaction of different categories of soil moisture (gravitational, capillary, film, adsorbed) with the pore space and solid components of the soil, represented by particles of different sizes with free surface energy.

For the first time, this analysis made it possible, not empirically, but physically-reasonably, to distinguish critical conditions in terms of moisture content on different soils with the change of physical forces and mechanisms controlling water retention, moisture availability to plants and microorganisms, its mobility, technological properties for the perception of external load (bearing capacity for machinery, buildings), resistance to mechanical processing (plowing, loosening), environmental and technological risks (salinization, man-made pollution, landslides, excess gas emissions) and other characteristics of the quality of soils.

The result of this theoretical analysis was a convenient table for agronomists, foresters, landscape designers with critical values of relative moisture content, which allows you to choose the optimal humidity range for virtually any Eurasian soil, in which the soil will perform the required technological and environmental functions and services, while ensuring that there is no damage to its quality and minimal unproductive losses of scarce water resources.

Journal Link: Agronomy 2021, 11(9)

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Agronomy 2021, 11(9)