Physical properties of soddy-podzolic soils in a long-term field experiment

The main physical properties of soddy-podzolic soils in a long-term field experiment have been studied. It is shown that their changes under the impact of a century-long application of lime, fertilizers, and manure have been relatively small. Reliable differences in the parameters of approximation of the dependence of penetration resistance on the soil water content in the variant with regular application of organic fertilizers have been revealed. This attests to stronger interparticle bonds (within the studied moisture range) in this variant. Interparticle bonds in the control variant and in the variant with lime application tend to increase with a decrease in the soil water content more significantly than those in other experimental variants. This may be due to the coarser texture of the soil in the control variant and to the aggregation of soil particles under the impact of lime in the variant with lime application.     

Diagnostics of manganese-iron nodules in soddy-podzolic soils at different degrees of gleyzation from their magnetic properties

The composition and magnetic properties of manganese-iron nodules in soddy-podzolic soils at different degrees of hydromorphism were studied. The data of chemical analysis, magnetic measurements, and X-ray diffraction analysis indicate that the nanoparticles of magnetite act as a strongly magnetic phase in these nodules. The distribution of strongly magnetic nodules in soils and the absence of correlation between the content of magnetite and the magnetic parameters of the enclosing soil material indicate that the nodule magnetite is of soil origin.     

Water budget items and temperature regime of postagrogenic soddy-podzolic soils of Moscow region and their effect on the soil properties

The postagrogenic transformation of the plow horizon of soddy-podzolic soils under a mown meadow and an artificially planted dense spruce stand has been studied in relation to the microclimatic specificity, water budgets, and soil temperature regimes in the compared cenoses. Over 20 years, a considerable part of precipitation reaching the soil surface under the meadow cenosis has been discharged with the surface runoff and subsurface lateral water flows. The soil warming in summer has been considerable, and the soil freezing in winter has been relatively weak. As a result, a gray humus horizon with well-shaped fine granular and coprolitic structure has been formed within the body of the former plow layer. Under the spruce stand, a larger part of atmospheric moisture has been infiltrated into the soil. The microclimatic conditions under the spruce stand have been more humid and colder. As a result, a thinner humus horizon with a considerable admixture of weakly decomposed plant debris has been formed in the upper part of the former plow layer. Below, a newly formed horizon with a specific thin platy (schlieren) structure ha been developed. The morphology of this horizon resembles the morphology of the eluvial horizon in virgin soddy-podzolic soils.     

Changes in the rheological properties and bulk density of soddy-podzolic soils under dynamic loads

Field studies of the rheological properties of loamy sandy soddy-podzolic soils were performed. Within the studied ranges of the soil moistening and bulk density values, the soils behaved as viscoelastic bodies. The dynamic deformation of such soils under compressive stress was modeled by a differential equation of the first order linking the compressive stress, the rate of its changes, and the relative soil deformation in the vertical direction. Correlative relationships between the viscoelastic soil properties, the soil bulk density, the soil water content, and the angular frequency of the harmonic law of the soil deformation were obtained. The methods of calculation of the soil bulk density as dependent on the initial bulk density and the mode of the soil deformation upon cyclic loads by rigid cylinders and by elastic wheels were developed. These methods were realized in a computer program for the quantitative assessment of the effect of the major factors on the changes in the rheological properties, the indices of the soil deformation, and the soil bulk density under the impact of compressive loads. It was shown that an increase in the number of loading-unloading cycles leads to the transformation of the viscoelastic soil properties into elastic properties.     

Changes in the acid-base properties of cultivated light-textured soddy-podzolic soils in the course of postagrogenic transformation

The rates of changes in the acid-base properties of the sandy-loamy soddy-podzolic soils of fallow lands abandoned for 5, 10, 30, and 63 years were determined. The transformation of the vegetation related to the fallow age has been analyzed. The density of the human-induced topsoil compaction was found to be gradually restored. Mathematical models describing the changes in the acid-base properties of the sandy-loamy soils in the course of the transition from cropland to forest are proposed. The sandy-loamy soils were shown to lose their favorable acid-base properties (gained under cultivation) more slowly than sandy soils do.     

Effect of long-term drainage on the content and composition of humus in soddy-podzolic soils and their particle-size fractions

Changes in the quantitative and qualitative characteristics of humic substances in soddy-podzolic soils and their particle-size fractions in the course of long-term drainage have been studied under the conditions of pronounced microrelief and different intensities of agrotechnical impacts. The transformation features of humic substances during the periods of specific impacts have been characterized.     

Postagrogenic transformation of organic matter in soddy-podzolic soils

In the chronological sequence of postagrogenic soils, the restoration of the original differentiation of the soil profile and its horizons proceeded with different rates depending on the fallow age and the horizon depth. The layer sampling (at 5-cm intervals) showed that the plow horizon began to differentiate into a system of subhorizons in all the fallow soils. The zonal pedogenesis showed clear signs of manifestation already in the 15-year-old fallow. The upper part of the former plow horizon in the 15- and 60-year-old fallows under herbaceous plants was transformed into a soddy horizon, while a postagrogenic soil 90 years old already developed under a zonal type of vegetation and approached the control soil in its morphological features. The content and reserve of carbon in the soils showed a stable tendency of increasing (especially in the upper part of the plow horizon) during the entire postagrogenic period under study. The water permeability of the soils gradually increased and approached that of the virgin soil. However, the compacted subsurface horizon (the plow pan) disappeared only after 90 years. The assessment of the physicochemical properties of the soils and the structural and functional parameters of the humic acids indicated the expansion of the layer differentiation primarily within the homogeneous plow horizon. From the elemental analysis and 13C NMR spectroscopy data, the degree of aromaticity in the molecular structure of the humic acids gradually decreased, and the aliphatic part developed with the age of the fallow.     

Re-evaluation of the structural properties of some British swelling soils

The structural condition of swelling soils can be assessed from their shrinkage curves. We re‐evaluated data on six British swelling soils using modern methods to model the void ratio, e, as a function of the moisture ratio, ?. The points on the e–? curve were fitted with a constitutive shrinkage equation using an unbiased least‐squares, curve‐fitting program. The shrinkage curves were then differentiated to obtain their slopes, σ(?), which were used to calculate the overburden potentials, Ω. The slope functions were subsequently differentiated to obtain the curvatures, κ(?), from which the maximum curvature at the wet end was used to separate the structural shrinkage, S_c, from the proportional (unsaturated) shrinkage. At the point of maximum curvature, S_c and the volumetric air content, θ_ac, were calculated and found to correspond closely to those reported previously. Water retention curves were constructed and fitted using the van Genuchten equation, from which the α coefficient appears an important structural parameter. The structural condition of a swelling soil appears to be well described by its air content at the point of maximum curvature, its van Genuchten α coefficient, and a parameter describing the effect of the overburden potential.     

Stimulation of nitrogen fixation in soddy-podzolic soils with fungi

Stimulation of nitrogen fixation in soddy-podzolic soils is related to the hydrolytic activity of fungi decomposing plant polymers. It was found that the rate of nitrogen fixation upon the simultaneous inoculation of the strains of nitrogen-fixing bacteria Bacillus cereus var. mycoides and the cellulolytic fungus Trichoderma asperellum into a sterile soil enriched with cellulose or Jerusalem artichoke residues is two to four times higher than upon the inoculation of the strains of Bacillus cereus var. mycoides L1 only. The increase in the nitrogen fixation depended on the resistance of the substrates added into the soil to fungal hydrolysis. The biomass of the fungi decomposing plant polymers increased by two–four times. The nitrogen-fixing activity of the soil decreased when the growth of the fungi was inhibited with cycloheximide, which attested to a close correlation between the intensity of the nitrogen fixation and the decomposition of the plant polymers by fungi. The introduction of an antifungal antibiotic, together with starch or with plant residues, significantly (by 60–90%) decreased the rate of nitrogen fixation in the soll.     

Regularities of the distribution of eroded and aggraded soddy-podzolic soils on slopes

The distribution of differently eroded soddy-podzolic soils on slopes of different gradients, lengths, and aspects has been studied with the use of a quantitative parameter of slope erodibility K. The latter is calculated as a product of slope gradient in the power of 1.3 and the length of the flow line (m) in the power of 0.5. It is shown that moderately eroded soddy-podzolic soils appear on the slopes of northern and northeastern aspects with K equal to 0.4; on the slopes of southern aspect, this parameter is somewhat lower (0.24). Moderately eroded soils prevail on the slopes of northern and northeastern aspects with K equal to 0.7.     

Effect of the long-term application of different fertilization systems on soddy-podzolic soils

The characteristics of the control variant of an acid nonlimed soil in which the pH values have remained stable for 40 years should be used as criteria for the maximum permissible loads of mineral fertilizers affecting the agrochemical and biological soil properties. Considerable alteration of these limiting agrochemical and biological soil properties (in the variant with NK application) leads to the soil degradation not only in the plow layer but also in the 1-m-deep layer. The application of lime, especially in combination with complete mineral fertilizer, prevents soil degradation, improves its properties, decreases the uptake of heavy metals by plants, and favors the production of ecologically clean agricultural products.     

Stable and labile components of humus in soddy-podzolic soils

A mathematical model was proposed to characterize the seasonal dynamics of the humus composition in loamy soddy-podzolic soils. The results of determining the composition of the organic matter during two successive seasons revealed the presence of labile and stable components in almost all the groups and fractions of the humic substances. The seasonal changes in the content of the humic substances, the exchangeable Ca, and the pH value at the equilibrium state of the soil were found to be identical during the successive years.     

The seasonal dynamics of yeast communities in the rhizosphere of soddy-podzolic soils

The annual dynamics of the number and taxonomic composition of yeast was studied in the rhizosphere of two plant species (Ajuga reptans L. and Taraxacum officinale Wigg.) in a forb-birch forest on soddy-podzolic soil. Eurybiont phyllobasidial cryptococci and red-pigmented phytobionts Rhodotorula glutinis were found to predominate in the phyllosphere of these plants, whereas the typical pedobionts Cryptococcus terricola and Cr. podzolicus occurred on the surface of roots and in the rhizosphere. The seasonal changes in the number and species composition of the yeast communities in the rhizosphere were more smooth as compared to those in the phyllosphere. In the period of active vegetation of the plants, the phytobiont yeasts develop over their whole surface, including the rhizoplane. Their number on the aboveground parts of the plants was significantly lower than that of the pedobiont forms. Thus, the above-and underground parts of the plants significantly differed in the composition of the dominant species of epiphytic yeasts.     

Variations in parameters and productivity of humus in soddy-podzolic soils with respect to microfeatures of topography and agrogenic impact

The long-term dynamics of humus parameters and bioproductivity of soddy-podzolic soils in an agrocenosis under the conditions of well-pronounced microfeatures of topography and agrotechnical impact of different intensity has been studied. Unfavorable changes in qualitative and quantitative parameters of humus in soils of depressions and their role in the productivity of phytocenoses have been analyzed. The difference between the pronouncement rate of humus degradation and a drop in productivity of phytocenoses in depressions in comparison with elevated areas and its dependence on the kind of agrotechnical impact has been revealed.     

Distribution of the particle-size fractions in soddy-podzolic soils subjected to sheet erosion

Tendencies in the formation of organomineral profiles of arable agrosoddy-podzolic soils on slopes in different denudation and accumulation zones were characterized on the basis of an integrated study of the humus status of the soils (using the granulodensimetric fractionation method), the content of clay, and the composition of clay minerals. It was shown that the organomineral and mineralogical parameters of the surface-horizon transformation could be used for improving the diagnostic accuracy of soils on the slopes basing on their conventional characteristics.     

Transformation of humic substances in soddy-podzolic soils under agrogenic impacts

The transformation of humic substances in soddy-podzolic soils under agrogenic impacts of different intensities and durations was studied. Indices of the initial stages of degradation and regradation of soil humus were revealed, and the humus status of soils under different fertilizing conditions was estimated.     

Spatial-temporal dynamics of organic carbon in soddy-podzolic soils of postagrogenic biogeocenoses

The organic carbon content in developed soddy-podzolic soils increased during the overgrowing of abandoned plowland with meadow and forest vegetation. The highest carbon content was recorded at the stage of 40–50-year-old forest, which was related to the largest input of organic matter into the soil and the intense litter decomposition during this period. A decrease in the soil carbon content was observed during the development of forest vegetation on the long-term hayfields in place of the former croplands, because the humus content in the lower part of the old-arable horizon decreased significantly. The spatial variability in the distribution of organic carbon in the soils increased with the development of forest biogeocenoses.     

Assessing the biological activity of oil-contaminated soddy-podzolic soils with different textures

The respiratory activity features in oil-contaminated soddy-podzolic soils of different textures have been studied. Unidirectional processes occur in contaminated loamy and loamy sandy soddy-podzolic soils; their intensities depend on the soil parameters. The mineralization rates of the oil products and the activity of the microflora in loamy soils exceed the corresponding parameters for loamy sandy soils. The long-term impact of oil and its transformation products results in more important disturbances of the microbial community in light soils. It has been shown that light soils containing 9% oil require longer time periods or more intensive remediation measures for the restoration of soil microbial cenoses disturbed by the pollutant.     

Influence of xenobiotics on the microbiological and agrochemical parameters of soddy-podzolic soil

We studied the influence of various chemical compounds, i.e., azobenzene (an insecticide and acaricide), nitrification inhibitors (DCD, dicyandiamide and DMPP, and 3,4-dimetylpyrazolphosphate), and inhibitors of urease activity (HQ-hydroquinone), on the agrochemical and microbiological parameters of a soddy-podzolic soil. It is proved that these xenobiotics are able to influence the agrochemical parameters (the pH and the content of NO₃⁻ and NH₄⁺, the microbial activity (the basal respiration, the microbial mass carbon, and the microbial quotient), and the number of bacteria of different physiological groups in soddypodzolic soil. The influence of the xenobiotics was preserved for some time, which testified to their persistence in the soil. Upon cultivating the soil microorganisms in different media, the growth of the heterotrophic bacteria was inhibited, the radial growth velocity was slowed down, and the sporogenesis of the micromycetes was retarded. The toxic effect of the xenobiotics was higher with their increasing concentrations.     

Dynamics of acid-soluble iron compounds in soddy-podzolic soils of the southern Komi Republic

The content of total iron and its contents in the Tamm, Mehra-Jackson, and 1 N H₂SO₄ extracts were determined for arable and forest soddy-podzolic soils with different degrees of gleyzation. The seasonal dynamics of the acid-soluble iron compounds in the soils were studied. It was found that the amount of iron extractable by 1 N H₂SO₄ was smaller than that passing into the Tamm and Mehra-Jackson solutions. The seasonal variation of the acid-soluble iron compounds in the humid years was significantly higher than in the dry years; it depended on the hydrological conditions of the year of observations and the soil density and degree of gleyzation. The temperature conditions of the year of observations had a lower effect on the content of the acid-soluble iron. The profile distributions of the acid-soluble and total iron depended on the vertical and lateral migration of water, as well as the meso- and microrelief conditions. An increase in the content of acid-soluble iron was observed under the decreased temperature in the spring and fall. The mobilization of iron under the effect of podzolization was activated during the period of the summer rains. In the third year of the agricultural development, the content of acid-soluble iron in the soils slightly decreased, which could be indicative of a decrease in the content of iron involved in the biological cycle under the development and drainage conditions. An exception was provided by the arable soils on the toeslope, where the content of acid-soluble iron was higher than that in the forest soils occupying analogous positions in the relief.