Articles

The features of soil and hydrological conditions of the solonetzic complex of the semi-desert of the Northern Caspian region, a long-standing object at 70-year monitoring of their natural and anthropogenic transformations, were studied at the Dzhanybek Research Station of the Institute of Forest Science of the Russian Academy of Sciences. The classical works of Professor A.A. Rode  and the research led by Professor T.A. Sokolova  became the standard for comparison when conducting it at the present stage. The soils of virgin areas and meadow-chestnut soils of micro- and mesorelief depressions under separated forest stand and massive forest plantation, mainly of pedunculate oak and squat elm, were studied. The data of weather and climatic conditions were analyzed, the coefficient of humidification of the territory was calculated, the dynamics of groundwater levels, their chemical composition and mineralization were traced, the composition of water extract from soils was determined and supplies of easily soluble salts and chlorine ion by half-meter layers were calculated. Three significantly different periods of changes in soil and hydrological conditions caused by fluctuations of the groundwater table and changes in moisture content in the region have been identified. The modern stage, which began in the early 2000s, turned out to be the driest with a moisture coefficient of 0.24±0.07. Against this background, the rise of the groundwater level characteristic of the early 80s of the XXth century was replaced by its lowering. Under meadow-chestnut soils of virgin depressions at a groundwater level of 5.6±0.2 m and their average mineralization of 3.41±0.27 gl-1, at the present stage, the previously appeared tendency of their salinization has been preserved due to the accumulation of Cl-, Ca2+, Na+ ions in them. In the depressions of the micro- and mesorelief under the separated and massive forest stands, there is an increase in groundwater mineralization caused by high evapotranspiration of the trees, but due to the additional accumulation of snow by forest strips and the periodically flushing type of water regime with limited desuction, a root-accessible desalinated zone with a thickness of 350 and 250 cm, respectively, persists there now. The revealed patterns, covering a 70-year period of observations, allow a more reasonable approach to the creation of demanded landscaping in such unfavorable climatic conditions.

Anthropogenic factors of soil acidification/alkalinization change the natural protolytic balance of soils. The degree and direction of such changes are determined by the magnitude of the acid/alkaline load and soil stability - acid-base buffering capacity. The article summarizes the results of a study of the sources of buffering capacity of taiga soils in the European north-east of Russia. It is shown that the buffering capacity of soils developing in the same climatic conditions, as well as similar in lithological features, depends on the hydrological conditions of the microrelief elements, and accordingly on the composition and functioning of biocenoses. The variability of the nature and structure of soil buffering is revealed in the thickness of the most active action of biotic factors - in organogenic and eluvial horizons. The similarity of illuvial horizons of genetically different and geographically isolated soils is due to their insignificant transformation by soil processes, which is manifested in the absence or reduced content of direct products of soil formation - organic, Al-, Fe-organic compounds, minerals of the soil chlorite group. The materials can be used for soil-chemical monitoring and for predicting soil changes under the influence of pollution by acidic and alkaline compounds.

The article is dedicated to the blessed memory of the outstanding scientist, teacher-mentor, professor, doctor of biological sciences Tatyana Alekseevna Sokolova. The scientific community knows and will always remember Tatyana Alekseevna as an authoritative specialist in the field of soil science and mineralogy. The scope of her interests in the scientific and educational system is wide and diverse. One of the fundamental areas of work is the problems of soil acidity. The presented material contains some components of the creative heritage of T.A. Sokolova in the aspect of current research and prospects for its development. In particular, attention is drawn to the nature of the acidity of highly acidic soils (pHKCl <3.3, pHH2O <4.4). The specificity of the formation of the acid-base state of these objects is shown using soils of different genesis as an example. The reasons for the low accuracy and reproducibility of the results of measuring the exchangeable acidity of highly acidic soils are revealed. Recommendations for improving the quality of measurements are given.

We tracked the effect and two-year aftereffect of potassium fertilizers with a single application under beet in rates of 70-240 kg∙ha-1 K2O in six farming trails of the Central Federal District, conducted in the Voronezh and Lipetsk Regions with sugar beet on soils with increased and high soil potassium levels. The contribution of potassium to the yield increase on average over three years was 14-15%. The content of exchangeable potassium during the experiments corresponded to a higher level of potassium supply compared to the available form, by one or two classes. The use of the potassium balance indicator for calculating the rates of fertilizers applied is advisable in years favorable for crop development. Calculation of optimal rates of potassium fertilizers obtained using multi-criteria estimation allows to consider 140 kg∙ha-1 K2O with a possible increase to 210 kg∙ha-1 in years favorable for crop development as the optimal for application to sugar beet in the Voronezh Region, and from 210 to 280 kg∙ha-1 K2O in the Lipetsk Region. A promising approach to determine potassium rates to jointly take into account the indicators of the effect and after-effect of fertilizers in terms of yield growth, economic efficiency, and the possibility of achieving a positive balance. The use of calculations based on only one of the above criteria, as well as on classes or direct assessments of soil potassium supply levels based on standard methods, leads to a significant overestimation or underestimation of the results due to the temporal instability of the determined indicators. Existing methods for calculating rates of potassium fertilizers require both the correction of the proposed classes of potassium availability and the consideration of the emerging potassium balance.

The study objects are represented by calcareous and weakly differentiated soils underlain by the hard carbonate-silicate rocks (red-colored and without reddish pigment ones) that have formed in the cold, continental environment of the southern part of the Lena-Angara plateau, Eastern Siberia. The study aimed to investigate the autochthonous/ allochthonous nature of the loose calcareous substrate underlain by the hard rock using data of clay mineralogy. Intensive leaching of carbonates in the soil profiles led to decrease of the pH values simultaneously with increase of the proportions of dithionite extractable iron in the topsoils. The clay mineral association is the same in the red-colored soil and calcareous hard rock. It represented by chlorite and dioctahedral mica (illite), and a small proportion of the mixed-layer illite-smectite (vermiculite) structures with < 50% of smectite (vermiculite) layers. The latter increases slightly in the soil horizons compared to the hard rock. Oppositely, clay mineralogy in the profile on the non reddish colored rock differs from that in the silicate part of the hard rock. Dioctahedral smectite, talc, dioctahedral mica, chlorite, and mixed-layer chlorite-vermiculite (smectite) were identified in the silicate part of the calcareous hard rock. In the soil horizons the decrease of the proportions of talc and smectitic clay was occurred. Besides, appearance of kaolinite in the soil horizons that is absent in the hard rock can be an indicator of the allochthonous substrate occurrence. The studied soils are illustrated two variants of pedogenesis on the loose calcareous substrate underlain by hard carbonate-silicate rocks: (i) on the eluvium of hard rock (red-colored profile) and (ii) with admixture of allochthonous loose substrate in the profile underlain by hard calcareous rock.

Middle and Upper Devonian (Voronezh, Belgorod regions of Russia) and Early and Middle Carboniferous (southern flank of Moscow sedimentary basin) paleosols were studied in detail. It was shown that the specificity of clay mineralogy of studied paleosols (with few exceptions) is their monomineral composition. Devonian terrestrial deposits and paleosols developed from them are kaolinitic, rare they have berthierine composition. Early Carboniferous paleosols are smectitic and Middle Carboniferous — palygorskitic. The mineralogy clear reflects the trends towards the aridization of climate and shifts in climatic zonation. Monomineral compositions and the absence of interstratification are the principal differences between Paleozoic, and Quaternary paleosols and modern soils developed from terrigenous deposits. The main reason behind it is the juvenile nature of Paleozoic paleosols from one side and the re-cycling of material from which Quaternary soils are developed – from other

The mineralogical composition of the silt fraction of marshes soils on the tombolo, a bridge between the mainland and a small island on the Pomorsky coast of the White Sea, has been studied. The soils on different parts of the marshes are characterized by different sequences of sediments and soil horizons embedded in them. Mica minerals (“illites”), kaolinite, chlorite and mixed-layer illite-vermiculite and chlorite-smectite were present in the silt fraction of all soils. Variation of mineralogical composition of clays was noted both between soil horizons and between the studied profiles. In our opinion, the variation is determined both by sediment composition and soil weathering of minerals, which confirms the idea of T.A. Sokolova about the complex character of formation of mineralogical composition of clays in soils on sediments re-deposited by water. The main weathering process in marsh soils was the degradation transformation of chlorite and, possibly, mica with the formation of smectite packages. These processes are spatially associated with the aeration zones of the marsh soils, at least periodically under oxidative regime.

The interaction of water-soluble organic matter (DOM) in aqueous extracts obtained from H horizon samples of peaty-podzolic-gleyic soil on kaolinite and muscovite were studied. The extracts contained different amounts of water-soluble Corg. mainly with molecular masses of about 20 kDa, represented mainly by hydrophilic compounds, but with different ratios of hydrophobic and hydrophilic components and with different concentrations of compounds containing aromatic structures. It has been established that the sorption of DOM components under the experimental conditions depends on the Сorg. concentration in the extracts, on the ratio of hydrophilic and hydrophobic components, on the mineral : solution ratio and practically does not depend on pH. Hydrophobic components and aromatic compounds are more sorbed on kaolinite surface compared to muscovite. The observed decrease of C org. sorption on both minerals when sorption per unit area of external surface in the experiments with the mineral : solution ratio of 1:50 in comparison with the ratio of 1:10 may indicate both the heterogeneity of sorption centers on the surface of minerals and the competition for these centers between the components of DOM. No significant changes in the curves of molecular weight components of DOM after interaction with kaolinite and with muscovite were revealed.

The fractionation of the clay fraction was carried out and the mineral composition of clay and its subfractions in the soil of the rhizosphere of the Norway maple (Acer platanoides L.) and in the bulk soil from the AELoa horizon of podzolic soil was studied. It was found that the clay fraction is dominated by a 1‒0.2 microns subfraction (56% in the rhizosphere of maple and 60% in the bulk soil) and contains 20% of 0.2‒0.06 microns subfraction in the rhizosphere and 27% of this fraction in the bulk soil. The content of 0.06‒0.02 and <0.02 microns subfractions did not exceed 10%. A significant increase was revealed in the proportion of 0.06‒0.02 microns subfraction and a decrease in the proportion of <0.02 microns subfraction in the rhizosphere compared with the bulk soil. The size fractions of clay both in the rhizosphere and in the bulk soil are differentiated by their mineral composition. The 1‒0.2 microns fraction is dominated by kaolinite; the proportion of micas increased and the proportion of kaolinite decreased in the 0.2‒0.02 microns fraction, while in the <0.02 microns fraction the proportion of labile minerals significantly increases. There was no significant difference in the mineral composition of the clay fraction and the 1‒0.2 microns subfraction. It was found that the 0.2‒0.02 microns subfraction in the rhizosphere contains significantly more labile minerals compared to the bulk one, which are a result of intensively occurring mica transformation processes into labile structures in the rhizosphere.