Rheological Properties of Automorphic and Semihydromorphic Cryometamorphic Northern Taiga Soils in Northeastern European Russia (Komi Republic)

Soil pastes at the water content corresponding to the maximum swelling of samples from different genetic horizons of cryometamorphic soils―surface-gleyic iron-illuvial svetlozem (Folic Albic Stagnosol) and peaty and peat humus-impregnated gleyic svetlozems (Histic Gleyic Stagnosols)―have been studied with an MCR-302 modular rheometer (Anton Paar, Austria). It has been found that the strongest interparticle bonds are formed in the horizons of cryometamorphic soils characterized by high contents of humic substances and organomineral Al–Fe–humus compounds. These are horizons of podzol microprofile (Eg and BHF) in iron-illuvial svetlozem and a humus-impregnated horizon (ELhi,g) in peaty and peat svetlozems. Organomineral Al–Fe–humus compounds, as well as the seasonal freezing of soils, determine the elastic-brittle character of interparticle interactions. The contents of clay fractions, exchangeable bases, and organic and organomineral substances impart viscoelastic properties to these contacts. An enhancement of elastic-brittle properties of soil is observed under the impact of gleying and freezing. The threefold decrease of the structural interaction parameter (∫Z) when going from automorphic to semihydromorphic conditions indicates a decrease in the resistance of peaty and peat svetlozems to mechanical loads under increasing hydromorphism compared to iron-illuvial svetlozems.     

Changes in some physical properties of a clay soil in Central Italy following the passage of rubber tracked and wheeled tractors of medium power

The aim of this study was to evaluate the compacting effect of rubber tracked tractors in comparison to that of the traditional wheeled tractors. Macroporosity, pore shape and size distribution, bulk density, penetration resistance and saturated hydraulic conductivity were analysed in a clay soil (Vertic Cambisol) near Rome (Italy) following one and four passes on the same track of rubber tracked and wheeled tractors of medium power. The soil structure attributes were evaluated by characterising porosity by means of image analysis of soil thin sections prepared from undisturbed samples. Macroporosity decreased in the 0–10 cm layer of compacted soil, particularly after four tractor passes, due to a large reduction in the proportion of elongated pores and in their vertical continuity. The rubber tracked tractor had a more pronounced compaction effect in the surface layer (0–10 cm) than the wheeled tractor both after one and four passes; the latter treatment producing the lowest soil porosity. The same trend was observed for hydraulic conductivity, which showed a highly significant correlation with elongated pores. In the 10–20 cm layer the porosity was significantly decreased following traffic, apart from in the soil under one pass of the rubber tracked tractor. Again in this layer, the lowest values of porosity were found in soil after four passes of the rubber tracked tractor. Single and multiple passes made by the two tractors induced different effects regarding soil penetration resistance and bulk density. Increment ratio of penetration resistance after tractor passes with respect to the control was: 12.5 and 49.9% with the wheeled and 34.4 and 39.8% with the tracked after one and four passes, respectively. Increment ratio of dry bulk density values after tractor passes with respect to the control was 7.9 and 11.7% with the wheeled and 7.5 and 8.3% with the tracked after one and four passes, respectively. The tractor passes transformed the initial subangular blocky structure into a massive structure with sometimes a platy structure in the upper few centimetres. The results indicated that soil compaction following traffic with the rubber tracked tractor was generally the more pronounced. However the compacting effect of this tractor after one pass seemed to be limited to the surface layer only.     

The role of frost boils in the development of cryozems on coastal lowlands of northern Yakutia

The influence of frost boils on the development of cryozems (Turbic Cryosols) in the tundra zone of northern Yakutia is discussed. Mechanisms of the input, redistribution, and transformation of raw organic matter with its accumulation in the deep part of the profile of cryozems are elucidated. As a result, specific organomineral or organic horizons are formed above the permafrost table. The development of cryozems has a cyclic pattern: from the stage of barren frost boil to the stage of mature soil profile. However, this cycle can be interrupted at any stage of overgrowing of the barren surface of frost boil. The rates of overgrowing and the formation of the profile of cryozem, and the ¹⁴C age of organic matter accumulated in the organomineral suprapermafrost horizons are estimated.     

The structure of two alluvial soils in Italy after 10 years of conventional and minimum tillage

Micro and macroporosity, pore shape and size distribution, aggregate stability, saturated hydraulic conductivity and crop yield were analysed in alluvial silty loam (Fluventic Eutrochrept) and clay soils (Vertic Eutrochrept) following long-term minimum and conventional tillage. The soil structure attributes were evaluated by characterizing porosity by means of image analysis of soil thin sections prepared from undisturbed soil samples.

The interaggregate microporosity, measured by mercury intrusion porosimetry, increased in the minimally tilled soils, with a particular increase in the storage pores (0.5–50 μm). The amount of elongated transmission pores (50–500 μm) also increased in the minimally tilled soils. The resulting soil structure was more open and more homogeneous, thus allowing better water movement, as confirmed by the greater hydraulic conductivity of the minimally tilled soils. The aggregate stability was less in the conventionally tilled soils and this resulted in a greater tendency to form surface crusts and compacted structure, compared with the minimally tilled soils. The latter tillage practice seemed to maintain, in the long-term, better soil structure conditions and, therefore, maintain favourable conditions for plant growth. In the silt loam, the crop yield did not differ significantly between the two tillage systems, while in the clay soil it decreased in the minimum tilled soil because of problems of seed bed preparation at the higher surface layer water content.     

Effect of the biota diversity on the composition of low-molecular-weight water-soluble organic compounds in southern tundra soils

Water extracts from the organic horizons of southern-tundra loamy permafrost-affected soils (a surface-gleyed tundra soil, a surface-gleyed soddy tundra soil (Haplic Stagnosols (Gelic)), and a peaty tundra soil (Histic Cryosol (Reductaquic)) and their undecomposed moss layers have been analyzed. The total weight concentration of the cations (Ca²⁺, Mg²⁺, K⁺, and Na⁺) determined by the atomic absorption method reaches 20 mg/dm³ in the organic horizons and 40–90 mg/dm³ in the undecomposed moss layers. Potassium and calcium ions dominate in all the organic horizons (80–90% of the total weight); potassium ions prevail in the mosses (about 70%). The weight concentration of carbon in the water-soluble organic compounds is 0.04–0.07 g/dm³ in the organic horizons and 0.20–0.40 g/dm³ in the undecomposed moss layers. The content of low-molecular-weight organic compounds (alcohols, carbohydrates, and acids) identified by gas chromatography and chromatomass spectrometry is 1–30 mg/dm³ in the organic horizons of the soils and 80–180 mg/dm³ in the mosses, which does not exceed 26% of the total organic carbon in the extracts.     

Pore morphology characteristics of vesicular horizons in undisturbed and disturbed arid soils; implications for arid land management

We compared the pore morphology of an arid lands vesicular soil horizon in a disturbed and undisturbed state. This surface vesicular horizon is characterized by non-connected pores that hinder soil water infiltration and thus plays a central role in arid ecosystem hydrodynamics. Disturbance is hypothesized to result in a change in pore morphology that could alter water movement through the horizon and potentially affect ecosystem function. To test this hypothesis, we examined the pore morphology of the vesicular horizon as expressed in area, perimeter, length and width; comparisons were also made for particle size, pH, calcium carbonate equivalent (CCE), electrical conductivity (EC) and the abundance and types of pores in undisturbed soils and adjacent disturbed soils within a year of disturbance. The results indicate no significant differences between treatments in chemistry, particle size or pore morphological measures within a year following disturbance. Vesicles, vughs and interstitial pores were found in vesicular horizons in both treatments and no significant differences in these parameters were found between treatments. Vesicular horizon development may be related to the geological age of the surface materials. Certain old land surfaces are perhaps more susceptible to the formation of vesicular horizons regardless of disturbance. The results suggest that soil functions dependent upon vesicular porosity, for example hydraulic conductivity, may return to a pre-disturbance condition within one year of disturbance, a finding of importance to the management of arid lands.     

Physical and morphological characterization of undisturbed and disturbed ploughpans in a sandy loam soil

In a sandy loam soil the ploughpan had a lower porosity and a higher bulk density and mechanical resistance than ploughpans that had been disturbed by rota-digging two years previously. Hydraulic conductivities (K) for pressure heads (h) from 0 to ?20 cm were higher and moisture contents within the same h range were lower. Both values were identical for pressure heads lower than ?20 cm. According to the widely used physical capillary pore model, the volume of pores > 140 μm was 2% (v/v) in the undisturbed ploughpan and 8% (v/v) in the disturbed ploughpan. However, micromorphometric analyses showed that the undisturbed ploughpan contained the highest volume of large pores and many continuous root channels, while the disturbed ploughpan had no continuous large pores. Pore continuity was determined by using a staining test with methylene blue. Disturbance of the ploughpan in these soils results in formation of unstable fragments, which collapse, thereby disrupting the vertical continuity of the initially large packing voids between fragments.     

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.     

Mercury in soils of British Columbia,a mercuriferous region

Mercury concentrations in various horizons of British Columbia soils were determined to estimate natural background levels in soils from various geographical areas of the province. Highly enriched concentrations near the Pinchi Lake cinnibar deposit declined to background levels ranging from 10 to 310 ppb Hg in the district. In six other regions, concentrations in surface mineral horizons averaged 85 ppb and ranged to 490 ppb but surface horizons of peaty muck soils and those predominated by vegetative litter contained 164 ppb Hg on the average and as much as 741 ppb. Concentrations in subsurface horizons were lower than at the surface. A significant relationship between Hg concentration and organic matter content was observed. Comparison with soils from outside British Columbia indicated its location within a generalized mercuriferous belt accounted for the relatively high concentrations observed.     

Persistence of soil compaction due to high axle load traffic. II. Long-term effects on the properties of fine-textured and organic soils

The long-term effects of high axle load traffic on soil structure were investigated in three field experiments. Two of the experiments were located on fine-textured mineral soils (Vertic Cambisol). The clay soil had 48 g clay (particle size less than 2 μm) per 100 g in the topsoil and 65 g per 100 g in the subsoil, and the loam soil had clay contents of 30 g and 42 g per 100 g in the topsoil and subsoil, respectively. One experiment was located on an organic soil (Mollic Gleysol) consisting of well-decomposed sedge peat mixed with clay from 0.2 to 0.4–0.5 m depth, and underlain by gythia (organic soil with high clay content). In the autumn of 1981, one pass and four repeated passes with a heavy tractor-trailer combination compacted the soils to 0.4–0.5 m depth. The trailer tandem axle load was 19 Mg on the clay and 16 Mg on the other soils.

For 9 years after the experimental traffic, the main crops grown were spring cereals. During this time, the maximum axle load applied during field operations was 5 Mg and the maximum tyre inflation pressure was 150 kPa. The clay and loam froze to 0.5 m depth for 6 and 2 years, respectively. During several growing seasons all three soils dried and cracked. In the ninth year after the loading, soil penetrometer resistance, saturated hydraulic conductivity (K_sat), macroporosity and number and area of cylindrical biopores were measured and the visual structure of the soils examined.

Compaction in the plough layer was alleviated by ploughing and natural processes, whereas in the subsoil the effects of the compaction were still measurable, in all experiments, in the ninth year after the high axle load traffic. In the clay soil in the 0.3–0.5 m layer and in the organic soil in the 0.28–0.4 m layer, the penetrometer resistance was 22–26% greater and the soil structure more massive in the plots compacted with four passes than in the control plots. In the 0.4–0.55 m layer in all soils, the loading with four passes decreased K_sat by 60–98% and macroporosity (diameter greater than 300 μm) by 37–70%. In the fine-textured mineral subsoils, cylindrical biopores were found in all treatments. The trend of the results was, however, for biopores to be fewer in compacted than in control plots.     

Compaction of forest soils with heavy logging machinery affects soil bacterial community structure

Soil compaction is widespread but tends to be most prevalent where heavy machinery is used in landfill sites, agriculture and forestry. Three forest sites strongly disturbed by heavy logging machinery were chosen to test the physical effects of different levels of compaction on soil bacterial community structure and soil functions. Community analysis comprised microbial biomass C and T-RFLP genetic profiling. Machine passes, irrespective of the compaction level, considerably modified soil structural characteristics at two soil depths (5–10 cm; 15–20 cm). Total porosity decreased up to 17% in the severe compaction. Reflected in this overall decline were large decreases in macroporosity (>50 μm). Reduction in macroporosity was associated with higher water retention and restricted gas exchange in compacted soils. The strongest effect was observed in the severely compacted wheel tracks where air and water conductivities were reduced permanently to 10% or even lower of the original conductivities of undisturbed soils. Very slow drainage in combination with a dramatically reduced gas permeability led to unfavorable soil conditions in severely disturbed traffic lanes reflecting the changes in the total bacterial community structures at both soil depths. Additionally, microbial biomass C tended to be lower in compacted soil. Our results indicate that the type of severe treatments imposed at these forest sites may have strong adverse effects on long-term soil sustainability.     

Composition and structure of aggregates from compacted soil horizons in the southern steppe zone of European Russia

The composition and structure of aggregates from different agrogenic soils in the southern steppe zone of European Russia have been studied. It is shown that the multi-level study (from the macro- to microlevel) of these horizons makes it possible to identify soil compaction caused by different elementary soil processes: solonetz-forming, vertisol-forming, and mechanical (wheel) compaction in the rainfed and irrigated soils. The understanding of the genesis of the compaction of soil horizons (natural or anthropogenic) is important for the economic evaluation of soil degradation. It should enable us to make more exact predictions of the rates of degradation processes and undertake adequate mitigation measures. The combined tomographic and micromorphological studies of aggregates of 1–2 and 3–5 mm in diameter from compacted horizons of different soils have been performed for the first time. Additional diagnostic features of negative solonetz- forming processes (low open porosity of aggregates seen on tomograms and filling of a considerable part of the intraped pores with mobile substance) and the vertisol-forming processes (large amount of fine intraaggregate pores seen on tomograms and a virtual absence of humus–clay plasma in the intraped zone)—have been identified. It is shown that the combination of microtomographic and micromorphological methods is helpful for studying the pore space of compacted horizons in cultivated soils.     

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.     

Physicochemical and Microbiological Characteristics of Tundra Soils on the Rybachii Peninsula

The Rybachii Peninsula is composed of Proterozoic sedimentary rocks and differs sharply from the rest of the Kola Peninsula in its geological structure, topographic forms, and parent rocks. It is dominated by Al–Fe-humus soils formed on moraines with an admixture of local rock fragments, including slates. Organic horizons of tundra soils in the peninsula are less acid than those on granitoids of adjacent mainland of the Kola Peninsula. The content of exchangeable calcium in the organic horizons varies from 17.4 to 68.0 cmolc/kg, and the content of water-soluble carbon reaches 400 mg/100 g amounting to 1–2% of the total soil organic matter content. The total number of bacteria in the organic horizons of tundra soils varies from 3.5 × 10⁹ to 4.8 × 10⁹ cells/g; and bacterial biomass varies from 0.14 to 0.19 mg/g. The length of fungal mycelium and its biomass in the organic horizons are significant (>1000 m/g soil). The biomass of fungal mycelium in the organic horizons exceeds the bacterial biomass by seven times in podzols (Albic Podzols) and by ten times in podbur (Entic Podzol), dry-peat soil (Folic Histosol), and low-moor peat soil (Sapric Histosol).     

黄河三角洲滨海盐渍土饱和导水率的研究

通过对黄河三角洲滨海盐渍土饱和导水率的研究, 结果表明: 原状土的饱和导水率随着土壤剖面深度的增加呈现出表土层高、中间土层低、底土层又升高的趋势; 扰动土与原状土的饱和导水率差异较大, 土壤饱和导水率与土壤容重呈负相关、而与孔隙度、结构系数、团聚度等均呈正相关。原状土的饱和导水率能反映田间水分运动以及孔隙状况, 对研究土壤水量平衡和水土保持有重要的意义。扰动土的饱和导水率对于土壤理化性质的理论研究有一定参考价值。     

滴灌条件下原状土与扰动土水分运动特性

为了分析土壤结构对土壤入渗规律的影响,通过研究云南红壤土滴灌条件下水分运动特征,采用室内外对比试验,试验共设计了3个滴头流量,分别为2.68,3.74,4.68L/h,土壤容重为1.2g/cm~3,分别进行了单、双点源滴灌入渗试验,着重分析了原状土与扰动土在一定的滴头流量下的湿润锋、湿润体变化特征,揭示区域土壤水分运移规律,进而为区域性作物灌水提供参考依据。结果表明:(1)原状土湿润锋运移速率比较快,原状土地表湿润比随交汇时间增加的速率快于扰动土,说明湿润锋的运移速率与土壤孔隙有关;(2)相同观测时间下,原状土湿润体变化比较快,原状土湿润体扁率α大于扰动土,原状土α=16.53%,扰动土α=45%;(3)原状土与扰动土含水率等值线变化有相同趋势,但不重合,疏密程度有差异;(4)原状土分形维数比扰动土的小,说明原状土孔隙分布差异大,扰动土的质地较均匀。研究结果揭示了该地区原状土与扰动土水分运动特征,为进一步的机理研究提供参考。     

The structure of bacterial communities in natural and anthropogenic brown forest soils of the Botanical Garden on Murav’eva-Amurskogo Peninsula

The microbiological characterization of the brown forest soils in the territory of the Botanical Garden-Institute of the Far East Division of the Russian Academy of Sciences in southern Primor’e is given. The high humus content and weakly acid reaction of these soils were shown to provide the optimal conditions for the development of bacteria. In the brown forest soils differing in the thickness of the humus horizons, all the ecologic-trophic groups of bacteria were present and the bacterial communities were highly diverse. The structure of the bacterial communities was identical in all the organomineral horizons of the soils and varied greatly by the seasons. In the anthropogenically disturbed soils, the share of corynebacteria, which are resistant to stress and capable of the destruction of xenobiotics, decreased.     

Effects of vehicle disturbance and soil compaction on Arctic collembolan abundance and diversity on Igloolik Island,Nunavut, Canada

Collembolan abundance and diversity in the Arctic are adversely affected by soil compaction and disturbance (vehicle tracks). In comparisons made with undisturbed soil (adjacent to the tracks) at two sites on polar semi-desert Arctic tundra: 1) Cemetery Ridge and 2) Arnaqquaksaat Point, on Igloolik island, Nunavut, Canada (69°22ˈN, 81°47ˈW), there were significantly fewer Collembola extracted from disturbed and compacted soils on the tracks (2 and 11 at sites 1 and 2, respectively) than from undisturbed soils (236 and 301 at sites 1 and 2, respectively). Collembolan species diversity was also lower on the vehicle tracks than off the tracks at both sites (2 and 5 versus 11 and 10, respectively). Values of Shannon–Weaver’s index for sites 1 and 2 were 0.70 and 1.30 on the tracks, but 1.54 and 1.44 off the tracks, and Simpson’s index also showed a similar pattern at 2.00 and 2.81 versus 3.47 and 2.95, respectively.     

The effect of soil compaction, profile disturbance and fertilizer application on the growth of eucalypt seedlings in two glasshouse studies

Soil damage, compaction and displacement, during logging or clearing and cultivation affects both soil physical and chemical properties and reduces growth of regenerated or planted tree seedlings. Understanding the factors involved will aid management and set limits for indicators of sustainable management in eucalypt forests. In the first of two glasshouse studies, three Eucalyptus species were grown for 110 days in soils from six forest sites in Tasmania, Australia. Sites sampled ranged from low rainfall dry forest to very high rainfall wet forest. Soil was collected from three soil depths, in 10 cm increments to 30 cm, each packed in pots to four different bulk densities, ranging from that present in undisturbed field sites to that plus 0.17 g cm⁻³. In the second study Eucalyptus globulus Labill. seedlings were grown in soil collected from disturbed and undisturbed sites, packed to two bulk densities, and fertilized with combinations of N and P. Increasing soil compaction, in Study 1, caused a proportional decrease in final mass of seedlings of up to 25%. Growth on soil from lower horizons (10–30 cm) averaged only 41% of that on topsoil, a significantly greater restriction of growth than that achieved through compaction. It was concluded that topsoil displacement and profile disturbance was a more significant form of soil damage than compaction. Above-ground dry weight of seedlings was most strongly correlated with soil total N but poorly correlated with other macronutrients. Growth of E. globulus seedlings grown on disturbed soils, in Study 2, averaged 30% of that on undisturbed sites. With added P and N on undisturbed sites growth averaged seven times that of the unfertilized seedlings indicating a general deficit of available P and N on the three soils tested. On soils from disturbed areas, there was also a response to fertilizing with N and P together but the response varied on the three soils. The effects of profile disturbance were ameliorated with fertilizer applications on only one of the soils. The results highlighted the importance of retaining topsoil in situ during forest operations.