Počvovedenie

Desert varnish or rock varnish is a thin reddish-black microlayer that cover rocks and is composed mostly of clay minerals, iron and manganese oxides. In this paper, both terms – desert and rock varnish – are used interchangeably. For more than two centuries, rock varnish has been an object of study and interest. Because it develops mainly in arid and desert areas, the interactions between radiation, wind, humidity and microbial activity are determining factors in its formation. On the other hand, the growth rates (few microns per millennium) suggest that it can function as a tool for recording past environments. The current work presents the state of knowledge of rock varnish focusing mainly on inorganic studies. The formation theories, geographical location, magnetic properties, lithodiversity, climatic variability, dating insights, pedofeatures, and some historical aspects are discussed. In addition, the different analytical techniques that have been used to study varnish chemical and mineralogical composition are grouped.

The present research provides information about distribution and fractionation of radium-226, uranium-238 and thorium-232 in the sod-podzolic-gley soil’s profile, as well as in different-sized fractions of manganese-ferrous ortsteins, which occupy 17% of the eluvial horizon soil mass. Fractionation of radionuclides was carried out using the Pavlotskaya method adding the fraction of organic matter. It is shown that radionuclides’ specific activities are distrubuted along the profile according to an eluvial-illuvial pattern. The content of biologically available (water-soluble and exchangeable fractions) and geochemically mobile compounds (water-soluble, exchangeable and mobile fractions) decreases in order radium-226 (11.9–28.5 and 15.3–32.5% of the total activities respectively) > uranium-238 (2.9–5.3 and 6.0–8.9%) > thorium-232 (0.2–4.4 and 1.1–7.4%). In compared to the host soil mass of eluvial horizon the ortsteins of all sizes accumulate the radionuclides; weighted average coefficients of the accumulation for radium-226, uranium-238 and thorium-232 are 2.1, 1.7 and 1.8 respectively. Regardless of the ortsteins’ size fractions, radium-226 is primarily increasing its content in the exchangeable compounds, uranium-238 – in the composition of the mobile fraction, while the uptake of thorium-232 depends on the neoformations’ size and occurs via mobile compounds and compounds, associated with organic matter and oxides of aluminum and iron. Within the soil profile the specific activities of the radionuclides significantly positively correlate with each other as well as with the content of eluvially-illuvially differentiated typomorphic elements, physical clay and silt, correlate negatively – with the content of manganese and organic matter. In the eluvial horizon direct correlation with iron and inverse correlation with calcium were shown for thorium-232.

Soil CO₂ emission was measured by the field chamber method in the experiment on application of no-till technology (without tillage) on chernozem soils of the Amur region of Russia, where 30% of the country’s soybeans are grown. One-factor and two-factor models for estimation of soil respiration per year were constructed based on the data of field measurements for 2022–2024. Soil temperature is a reasonably good predictor of emission (R² = 0.8, p < 0.001), which allows us to use continuous soil temperature series from loggers to calculate seasonal fluxes at a frequency of 6 times per day. Total annual flux in the experimental plot (no-till) was 0.69 t C/ha or 23.6% lower than in the control plot (conventional tillage). The contribution of the summer period to the annual flux was 59%. The two-factor T&P-model (temperature and precipitation) showed an overestimation of annual flux by 40%. Application of air temperature from the nearest weather station for modeling gave an underestimation of total flux by 13–20%. The no-till plot showed higher water-soluble carbon (2.5 and 3.8%, p = 0.055) and nitrogen (0.3 and 0.6%, p = 0.0025) relative to the conventional plot. Switching to no-till technology increases the density of the upper soil horizons by 8–12%, but the density remains within the optimum for soybean. In the no-till plot, soil volumetric moisture is also consistently higher (by 38% on average in the 0-5 cm layer), which is a strategically important advantage due to frequent periods of moisture deficiency.

The influence of salt composition on the enzymatic activity of soils of the Astrakhan region: solonchaks (Haplic Solonchaks (Aridic)), brown arid (Endosalic Calcisols) and alluvial sod (Calcic Fluvisols) soils. Ten soil samples taken from the upper soil layer (0–20 cm) from the territory of the Narimanovsky, Trusovsky and Privolzhsky districts of the Astrakhan region were examined. Sulfate and sulfate-chloride types of salinization predominate in the studied soil samples. In the non-saline alluvial sod soil of the Volga region of the Astrakhan region, the maximum integral index of enzymatic activity was found for all enzyme classes (87%), while in a similar soil with an average degree of salinity its value was 1.5 times lower and approached that in Solonchaks. Under soil salinization, the enzymes of the C cycle (invertase, dehydrogenases), N (urease), S (arylsulfatase) and P (phosphatase) showed the greatest sensitivity, and the enzymes of the O cycle (ascorbate oxidase and peroxidase) showed the least sensitivity. The use of enzyme activity in saline soils as a diagnostic indicator is possible considering the type of soil, the chemistry of salinity, and the cationic and anionic composition of the soil.

Urup Mining and Processing Plant is the largest enterprise in the South of Russia for the extraction and processing of copper pyrite, the waste of which contains high concentrations of heavy metals. As a result of their migration, the soil bordering the existing tailing dump is polluted. The work estimates the degree of contamination of the upper 10 cm layer of mountain meadow chernozem soil (Mollic Leptosol) with 48 potentially toxic elements (PTE) depending on the distance from the tailings dump and the impact of pollution on the biological properties of the soil. The priority pollutants with which the soil is most polluted have been identified: at a distance of 5 m from the tailings dump, the Ag content in the soil is 63 times higher than in the background soil; Sb – 25; Hg – 23; Cu – 19; Te – 19; Zn – 14; Cd – 14; As – in 13; Mo – in 12; Pb – in 6; Sn – in 3.7; Bi – in 3.6. At the same time, at 300-400 m from the tailings dump, soil pollution is no longer observed. The degree of decrease in biological indicators of soil condition (activity of catalase, dehydrogenase, invertase, urease, total number of bacteria, abundance of bacteria of the genus Azotobacter, germination, length of roots and shoots of radish seedlings, etc.) correlates with the content of PTE in it. As we move away from the tailing dump, the biological properties of the soil improve. The abundance of bacteria of the genus Azotobacter, the activity of dehydrogenases and invertase are the most sensitive to polymetallic contamination of mountain meadow soil from the Urupsky mining and Processing Complex, and the activity of dehydrogenases, catalase, and invertase is the most informative (correlating with the content of PTE in the soil).