Paramagnetic properties of humus acids of podzolic and bog-podzolic soils

The contents of free radicals in preparations of humic and fulvic acids extracted from virgin and plowed podzolic, surface gleyic podzolic, and peaty podzolic-gleyic soils were determined. The concentration of paramagnetic centers in the humic acids was 1.5–2 times higher than that in the fulvic acids. The agricultural use decreases the paramagnetic activity of the humus compounds and promotes the accumulation of biothermodynamically stable organic compounds in the plow horizons.     

Pedogenic chlorites in podzolic soils with different intensities of hydromorphism: Origin,properties, and conditions of their formation

Minerals of the pedogenic chlorite group were studied in the clay fractions isolated from the mineral horizons of podzolic and gleyic peat-podzolic soils. In the AE and E horizons of the podzolic soil, pedogenic chlorites are thought to develop from vermiculite, whereas in the E horizon of the gleyic peat-podzolic soil, they can be formed from smectite minerals. For estimating the degree of chloritization (the degree of filling of the interlayer space of 2: 1 minerals with Al hydroxides), a numerical criterion was is proposed. The difference between the values of this criterion before and after the treatment of the preparations with NH₄F indicated that the degree of chloritization in the pedogenic chlorites decreases in the following sequence: the E horizon of the podzolic soil > the AE horizon of the podzolic soil > the E horizon of the gleyic peat-podzolic soil. Another numerical criterion was proposed to estimate the degree of polymerization of Al-hydroxy complexes in pedogenic chlorites. This criterion was based on the thermal stability of soil chlorites and represented the temperature at which an increase in the intensity of the 1.0-nm peak after heating the K-saturated preparations exceeds 50% of its initial value. According to this criterion, the degree of polymerization of the Al-hydroxy interlayers in pedogenic chlorites decreases in the following sequence: the E horizon of the podzolic soil > the E horizon of the gleyic peat-podzolic soil ≥ the AE horizon of the podzolic soil. The distinct interrelation between the soil properties and the degrees of chloritization and polymerization of the Al-hydroxy interlayers attests to the modern origin of the pedogenic chlorites.     

Acid-base buffering of soils in transitional and transitional-accumulative positions of undisturbed southern-taiga landscapes

The method of continuous potentiometric titration (CPT) of soil water suspensions was used to evaluate the acid-base buffering of samples from the major genetic horizons of podzolic soils on a slope and soddy gley soils on the adjacent floodplain of a rivulet. In the soils of the slope, the buffering to acid upon titration from the pH of the initial titration point (ITP) to pH 3 in all the horizons was 1.5?C2.0 times lower than that in the podzolic soils of the leveled interfluve, which could be due to the active leaching of exchangeable bases and oxalate-soluble aluminum and iron compounds with the later soil flows. In the soddy gley soils, the buffering to acid in the mineral horizons was 2?C10 times higher than that in the podzolic soils. A direct dependence of the soil buffering to acid on the total content of exchangeable bases and on the content of oxalate-soluble aluminum compounds was found. A direct dependence of the buffering to basic upon titration from the ITP to pH 10 on the contents of the oxalate-soluble aluminum and organic matter was observed in the mineral horizons of all the studied soils. The soil treatment with Tamm??s reagent resulted in the decrease of the buffering to acid in the soddy gley soils of the floodplain, as well as in the decrease of the buffering to basic in the soils on the slopes and in the soddy gley soils. It was also found that the redistribution of the mobile aluminum compounds between the eluvial, transitional, and transitional-accumulative positions in the undisturbed southern taiga landscapes leads to significant spatial differentiation of the acid-base buffering of the mineral soil horizons with a considerable increase in the buffer capacity of the soils within the transitional-accumulative terrain positions.     

Polycyclic aromatic hydrocarbons in background podzolic and gleyic peat-podzolic soils

The qualitative and quantitative composition of polycyclic aromatic hydrocarbons (PAHs) has been determined in the background podzolic and gleyic peat-podzolic soils of the middle and northern taiga zones of northeastern Europe using the methods of highly efficient liquid chromatography and chromato-mass spectrometry. The distribution of polyarenes in the soil profiles follows the eluvial-illuvial pattern. Organic and illuvial horizons are the biogeochemical barriers for PAHs migrating in the soils. The revealed regularities of the accumulation and redistribution of PAHs in the soil profiles are in agreement with the character of the soil-forming processes in the northern and middle taiga zones.     

Comparative analysis of the composition of water extracts and soil solutions from peat gleyic podzolic soils of the Central Forest State Biosphere Reserve

The composition of soil solutions obtained by vacuum filtration from peat gleyic podzolic soils of the Central Forest State Biosphere Reserve under field conditions was determined. It was found that the composition and properties of the soil solutions reliably differ from those of the water extracts. The natural solutions are characterized by higher concentrations of metals (primarily of Na, K, Ca, and Cu), an increased content of the hydrophobic fraction of water-soluble substances, an order of magnitude lower carbon content, and lower values of the actual and potential acidity.     

Evolution of surface properties and organic matter stabilisation in podzolic B horizons as assessed by nitrogen and phosphate sorption

In podzolic B horizons illuviated Al, Fe and organic matter (OM) increase with the ongoing of the pedogenic process. Depending on OM load on mineral surfaces, modifications of the soil surface properties are expected and may influence OM stabilisation. The proportion of labile organic pools should thus vary depending on the type of podzolic horizon. In this work, we selected B horizons at increasing intensity of podzolisation, evaluated the labile OM pools through oxidation with 2 % NaClO and characterised surface properties with N₂ and phosphate sorption. Before and after oxidation, we assessed the NaOH-extractable OM fractions. Oxidation was more effective on the least polar organic compounds and led to an increase in the fulvic to humic acid ratio. Specific surface area (SSA) increased after oxidation only in the least podzolised horizons, while selectively preserved OM induced a decrease in SSA in the more developed Bs, Bsm and Bhs. Phosphate sorption induced a release of OM and always decreased after oxidation, although variations in P affinity for the surfaces were observed. The effect of oxidation on surface parameters pointed to a specific association between organics and minerals that changed during soil development. At the very beginning of podzolisation, the dominant forms seemed related to organo-metallic complexes with little interaction with surfaces. With Bs development, weak interactions between mineral surfaces and OM appeared, while at a later stage OM differentiated into bulky structures and tightly bound, rigid ones, with extremely low N₂ accessibility. The latter were not sensitive to low concentration NaClO while the former were easily oxidised.     

The effect of soil type on phosphorus sorption capacity and desorption dynamics in Irish grassland soils

Abstract. The phosphorus (P) sorption and desorption dynamics of eleven major agricultural grassland soil types in Ireland were examined using laboratory techniques, so that soils vulnerable to P loss might be identified. Desorption of P from soil using the iron-oxide paper strip test (Pfeo), water extractable P (Pw) and calcium chloride extractable P (Pcacl₂) depended on soil P status in all soils. However, soil types with high organic matter levels (OM), namely peat soils (%OM >30), had lower Pfeo and Pw but higher Pcacl₂ values compared to mineral soils at similar soil test P levels. Phosphorus sorption capacity remaining (PSCr) was measured using a single addition of P to soils and used to calculate total P sorption capacities (PSCt) and degree of P saturation (DPS). Phosphorus sorption capacities correlated negatively with % OM in soils indicating that OM may inhibit P sorption from solution to soil. High organic matter soils exhibited low P sorption capacities and poor P reserves (total P, oxalate extractable P) compared to mineral soils. Low P sorption capacities (PSCt) in peat soils were attributed to OM, which blocked or eliminated sorption sites with organic acids, therefore, P remained in the soil solution phase (Pcacl₂). In this work, peat and high organic matter soils exhibited P sorption and desorption characteristics which suggest that these soils may not be suitable for heavy applications of manure or fertilizer P owing to their low capacities for P sorption and storage.     

Mobile aluminum compounds in soils of the southern taiga (soils of the central forest reserve as an example)

The profile distributions of aluminum extracted by the Tamm and Bascomb reagents and of the exchangeable aluminum were studied in soils of automorphic, transitive, and accumulative positions in the landscapes of the southern taiga. In the mineral horizons of the gleyic peaty-podzolic soils developed on poorly drained flat surfaces and in the floodplain soils, the distribution of oxalate- and pyrophosphate-soluble aluminum has a strongly pronounced accumulative character. In the podzolic soils of the automorphic positions and slopes, an eluvial-illuvial distribution was characteristic with the maximal aluminum content in the podzolic horizons. The strong differentiation of the upper part of the profile in the automorphic podzolic soils in terms of the Al content in the Tamm and Bascomb extracts is mainly related to an increase of the pedogenic chlorite content upon the transition from the AE to the E horizon. In the podzolic horizons of these soils, aluminum can accumulate in the form of proto-imogolite structures. The exchangeable aluminum displays an accumulative type of distribution. On the basis of calculating the reserves of the different aluminum compounds, two main accumulative zones for the mobile compounds of this element were recorded in the soils of the landscapes studied: the E horizon in the automorphic podzolic soils, where Al accumulates as soil chlorite or, probably, as proto-imogolite, and the A1 horizon of the floodplain soils, where Al accumulates in aluminoorganic complexes.     

The acid-base buffer capacity of podzolic soils and its changes under the impact of treatment with the Mehra-Jackson and Tamm reagents

The acid-base buffer capacity before and after the treatment with the Mehra-Jackson and Tamm reagents was assessed by continuous potentiometric titration for the main genetic horizons of two profiles of podzolic soils in the Central Forest State Reserve. The total buffer capacity was calculated in the pH range from the initial titration point (ITP) to 3 for the acid titration and from the ITP to 10 for the base titration, as well as the buffer capacities in the pH intervals of 0.25. It was found that both treatments abruptly decreased the base buffer capacity, which reached 70–90% in the E horizons. The high direct linear correlation of the difference between the total base buffer capacities before and after each treatment with the content of Fe in the Tamm extract was revealed. From the results obtained, a conclusion was drawn that finely dispersed Fe hydroxides were the main solid-phase constituents ensuring the base buffer capacity, and the deprotonation of hydroxyl groups on the surface of Fe hydroxides was the essential buffer reaction during the base titration.     

Aluminum compounds in soil solutions and their migration in podzolic soils on two-layered deposits

The fractional composition of aluminum compounds was studied in soil solutions obtained using vacuum lysimeters from loamy podzolic soils on two-layered deposits. The concentration of aluminum was estimated in brooks and a river draining the area with a predominance of these soils. In soil solutions, the concentration of aluminum was experimentally determined in the following compounds: (1) organic and inorganic monomers, (2) stable complexes with HAs and FAs together with polymers, and (3) the most stable complexes with HAs and FAs together with fine-crystalline and colloidal compounds. The total Al concentration in soil solutions from forest litter was 0.111–0.175 mmol/l and decreased with depth to 0.05 mmol/l and lower in solutions from the IIBD horizons. More than 90% of the Al in the solutions was bound into complexes with organic ligands. Some amount of Al in solution could occur in aluminosilicate sols. The translocation of Al complexes from the litter through the AE horizon to the podzolic horizon was accompanied by an increase in the ratio between the Al concentration in fraction 2 and the C concentration in the solution. The concentrations of Al_tot in the surface waters varied in the range from 0.015 to 0.030 mmol/l. Most of the Al came to the surface waters from the litter and AE horizons and partially from the podzolic horizon due to the lateral runoff along the waterproof IIBD horizon. Approximate calculations showed that the recent annual removal of Al from the AE and E horizons with the lateral runoff was 7 to 560 mg (3–21 mmol) from 1 m².     

Mineralization of soil organic matter initiated by the application of an available substrate to the profiles of surface and buried podzolic soils

The priming effect (PE) initiated by the application of ¹⁴C-glucose was studied for copiotrophic microbial communities of organic horizons and for oligotrophic microbial communities of mineral soil horizons, as well as for mineral horizons of buried soils depleted in the input of fresh organic matter. The intensity of the PE depended on the reserves of C_org, the initial amount of the microbial biomass, and the enzymatic activity, which decreased from the organic to the mineral soil horizons. The ratio of the PE to the applied carbon was two times higher in the mineral horizons as compared with the organic horizons. This is explained by the predominance of K-strategists capable of decomposing difficultly available organic compounds in the mineral horizons, so that the turnover of the microbial biomass in the mineral horizons was more active than that in the organic horizons. The predominance of K-strategists was confirmed by the close correlation between the PE and the activity of the cellobiohydrolase enzyme decomposing cellulose (R = 0.96). In general, the absolute value of the PE was controlled by the soil organic matter content, whereas the specific PE was controlled by the functional features of the microorganisms. It was shown that the functional features of the soil microorganisms remained unchanged under the conditions of their preservation in the buried soil.     

Phosphate status of chernozem-like hydromorphic soils in the northern Tambov Plain

The phosphate status of chernozem-like soils in the northern forest steppe of the Tambov Lowland depends on soil waterlogging and hydrological conditions. Due to surface waterlogging and free effluent seep-age in podzolized, chernozem-like soils of open watershed depressions, the removal of bases and iron decrease the total phosphorus content by 10–15% because of the decrease in active mineral phosphates. Organic matter acts as a buffer preventing phosphorus from leaching. In podzolized, chernozem-like and podzolic, gleyic soils of closed watershed depressions, significant amounts of iron phosphates are accumulated in fine earth and ortsteins due to surface waterlogging and difficult effluent seepage. Under ground waterlogging, calcium phosphates prevail in the composition of active mineral phosphorus in the gleyed, gleyic, and gley chernozem-like soils of above-floodplain terraces.     

Polycyclic aromatic hydrocarbons in pyrogenic soils of swampy landscapes of the Meshchera lowland

The composition and distribution of polycyclic aromatic hydrocarbons (PAHs) were studied in organomineral and organic soils of the Meshchera National Park. It was found that the background oligotrophic peat soils unaffected by fires in central parts of the bogs are characterized by the increased PAH concentrations due to their high sorption capacity. The fires of 2007 and 2010 resulted in the transformation of the plant cover and soil morphology, the formation of new horizons, and the change in the PAHs content and composition. Significant burn-off of organic matter was found in oligotrophic-eutrophic soils and resulted in the decrease of PAHs content after fire. Only partial burn-off of organic horizons and intense formation of PAHs were recorded in the soil with initially great thickness of peat horizons. Pyrogenic accumulation of PAHs was identified in organomineral soils of the marginal parts of bogs and of forest sites.     

Peat soils: Genesis and classification

This paper considers three topical problems—the definition of peat soils as natural-historical formations and the estimation of their profile thickness, the analysis of the genesis of organic soils, and the principles of the classification of peat soils. Based on the experimental data of long-term studies, it was concluded that peat soils may include the whole peat layer and the upper horizons of the surface mineral soil. The organic and mineral parts of the natural structures were found to be a genetically homogeneous soil profile, which has the same history of development. The upper layer of the peat soils should be considered as the horizon reflecting the contemporary stage of the soil formation. A hierarchy of peat soils is analyzed for developing their classification.     

Rheological features of the coagulative structure of northern taiga peaty podzolic semi-gley soils of the European Northeast

The results of rheological studies using a MCR 302 modular research rheometer of soil pastes of northern taiga peaty podzolic semi-gley soils are presented. It was found that their coagulative structure has weak structural links. They are little resistant to mechanical stress and their stability decreases in the direction from the northern to the extreme northern taiga by about two times. The strongest coagulative links between soil particles characterize the horizons with increased organic contents and the horizons that are transient in terms of granulometric composition, which lie at the border where light deposits shift heavier ones.     

Short-term controls over inorganic phosphorus during soil and ecosystem development

Geochemical sorption and biological demand control phosphorus (P) retention and availability in soils. Sorption and the biota predominantly utilize the same inorganic form of P, from the same soil pool, on the same time scale, and thus are likely to compete for P as it flows through the available pool. In tropical soils, P availability is typically quite low and soil geochemical reactivity can be quite high. We tested whether greater P sorption strength in tropical soils resulted in lower biological uptake of available P. Since the strength of soil sorption and biological demand for P change as ecosystems develop and soils age, we used soils from the two upper horizons from three sites along a 4.1 million-year-old tropical forest chronosequence in the Hawaiian archipelago. We evaluated the strength of geochemical sorption, microbial demand, and the partitioning of added available P into biological versus geochemical soil pools over 48 h using a ³²PO₄ tracer. Soil sorption strength was high and correlated with soil mineral content. The amount of added phosphate geochemically sorbed versus immobilized by microbes varied more between the organic and mineral soil horizons than among soil ages. Microbial activity was a good predictor of how much available P was partitioned into biological versus geochemical pools across all soils, while sorption capacity was not. This suggests that microbial demand was the predominant control over partitioning of available P despite changes in soil sorption strength.     

Anisotropy of the properties of some anthropogenically transformed soils of podzolic type

It is shown that the horizons and profiles of anthropogenically transformed soils of podzolic type—light typical agrozems, typical texture-differentiated soils developed from glaciolacustrine loamy sands and clays and from noncalcareous mantle loams, agrosoddy deeply podzolic soils developed from noncalcareous mantle loams, and agrosoddy shallow-podzolic soils developed from noncalcareous mantle loams and from calcareous loams underlain by ancient glaciolacustrine loams and clays—are characterized by some anisotropy of most of their properties. The highest anisotropy is typical of the field water content, bulk density, and total porosity. The coefficients of anisotropy (gradients) calculated for the separate horizons as the ratios between the values of the properties measured in the horizontal and vertical directions (k = P_horiz/P_vertic) of these properties are much higher than those of other soil properties. The coefficient of anisotropy of the soil profile (K) is suggested as the coefficient of correlation between the values of a given property determined in the horizontal and vertical soil sections. For the considered properties, K varies from 0.4 to 0.6. For other soils properties, such as the solid phase density, the electrical resistance determined in a laboratory and in the field, and the organic carbon content, the coefficients of anisotropy are close to 1.0. The clay content has an intermediate anisotropy. The values of anisotropy and its direction (gradient) should be taken into account upon the assessment of the soil physical properties and the processes controlling them; this is particularly important in the study of soil transformation. The revealed regularities of the soil anisotropy make it possible to suggest a new interpretation of the data on the distribution of water and energy in soil profiles.     

Contribution of different proton sources to pedogenetic soil acidification in forested ecosystems in Japan

The contribution of different proton sources to pedogenetic soil acidification was evaluated for three Japanese forest soils, i.e. ando soil, podzolic soil and brown forest soil in relation to the respective soil forming processes. Soil acidification rate and net proton generation were quantified based on the theory of proton budget for the respective soil horizon compartments (mainly the O, A and B horizons) by measuring fluxes of solutes entering and leaving the soil horizon compartment and vegetation uptake. Protons were produced by the dissociation of organic acids and nitrification in the O horizon and then consumed by adsorption and decomposition of organic acids and nitrate uptake by vegetation in deeper soil horizons at all plots. Excess uptake of cation over anion by vegetation was highest among proton sources in the whole soil compartment at all plots. Pedogenetic soil acidification was considered to include cation leaching from surface soil horizons due to proton generation by the dissociation of organic acids and nitrification and subsequent cation excess accumulation in wood in the growth stage of forests. In ando soil, andosolization resulted from the low contribution of net proton generation by the dissociation of organic acids as well as a lower soil acidification rate and complete acid neutralization. Dissolved organic carbon (DOC) fluxes in ando soil were lower than those in podzolic soil and brown forest soil due to high adsorption capacity of amorphous materials. In podzolic soil, podzolization resulted from intensive acidification in the O horizon, which derived from net proton generation by the dissociation of organic acids and nitrification as well as cation excess uptake by vegetation due to concentrated fine root biomass in the O horizon, and subsequent high proton efflux to subsoil. The high fluxes of DOC and Al leached from surface soil horizons were considered to contribute to eluviation of Al from surface soil and illuviation in subsoil in podzolic soil. In brown forest soil, brunification resulted from a lower DOC flux from the O horizon due to high decomposition and adsorption by oxides, where podzolization was weakened by high acid neutralization. Thus, the three representative processes involved in the pedogenesis of Japanese forest soils were well characterized by quantification of the respective proton-generating and consuming processes in each soil horizon.     

Contributions of separate reactions to the acid–base buffering of soils in brook floodplains (Central Forest State Reserve)

The acid–base buffering of gleyic gray-humus soils developed in brook floodplains and undisturbed southern-taiga landscapes has been characterized by the continuous potentiometric titration of soil water suspensions. During the interaction with an acid, the major amount of protons (>80%) is consumed for the displacement of exchangeable bases and the dissolution of Ca oxalates. In the O and AY horizons, Mn compounds make the major contribution (2–15%) to the acid buffering. The buffer reactions with the participation of Al compounds make up from 0.5 to 1–2% of the total buffering capacity, and the protonation of the surface OH groups of kaolinite consumes 2–3% of the total buffering capacity. The deprotonation of OH groups on the surface of Fe hydroxides (9–43%), the deprotonation of OH groups on the surface of illite crystals (3–19%), and the dissolution of unidentified aluminosilicates (9–14%) are the most significant buffer reactions whose contributions have been quantified during the interaction with a base. The contribution of the deprotonation of OH groups on the surface of kaolinite particles is lower (1–5%) because of the small specific surface area of this mineral, and that of the dissolution of Fe compounds is insignificant. In the AY horizon, the acid and base buffering of soil in the rhizosphere is higher than beyond the rhizosphere because of the higher contents of organic matter and nonsilicate Fe and Al compounds.     

Distribution of rare-earth (Y,La, Ce) and other heavy metals in the profiles of the podzolic soil group

Along with Fe and Al, many heavy metals (Mn, Cr, Zn, Cu, and Ni) show a markedly pronounced eluvial-illuvial redistribution in the profiles of soils of the podzolic group. The intensity of the redistribution of the bulk forms of these metals is comparable with that of Fe and exceeds that of Al. Although the podzolic soils are depleted of rare-earth metals, the latter respond readily to soil podzolization. The inactive participation of Al is explained by an insignificant portion of the active reaction-capable fraction. Podzolization does not influence the profile distribution of Sr and Ba. The leaching degree of heavy metals such as Mn, Cr, Zn, Ni, and Zr is noticeably higher in the sandy podzols than in the loamy podzolic soils. Leaching of heavy metals from the podzolic horizons is of geochemical importance, whereas the depletion of metals participating in plant nutrition and biota development is of ecological importance. The leaching of heavy metals is related to the destruction of clay particles in the heavy-textured podzolic soils; the effect of the soil acidity on the leaching of heavy metals is less significant.