Genesis of soils developed from red-brown clays and loesslike loams in the southwest of the Central Russian plain (the Belogor’e reserve)

Soils developed from the red-brown Neogene clay and the Quaternary loesslike loams have been studied in the south of the forest-steppe zone on the Central Russian Upland. A polygenetic nature of the soil profile on the loesslike loams is shown. The modern pedogenetic processes in this soil ensure its eluvial-illuvial differentiation with the development of multilayered coatings in the illuvial horizon. The soil developed from the Neogene clay has a lower degree of differentiation despite the more acid reaction. The micromorphological study of the coatings and the mineralogical analysis of the clay fraction separated from the coatings and from the intraped mass disclose differences in the geneses of B horizons of the two soils. In the soil developed from the loesslike loam, hydromica predominates among clay minerals of the coatings; in the soil developed from the red-brown clay, smectitic minerals predominate in the clay fraction. Differences in the properties of these two parent materials predetermined differences in the major directions of soil formation: the metamorphic pedogenesis predominates on the red-brown clay, whereas the textural differentiation develops in the soil on the loesslike loam. The middle horizons in the studied soil profiles are referred to as the structural-metamorphic and textural (clay-illuvial) horizons, respectively.     

Changes in the geometric structure of pores and aggregates as indicators of the structural degradation of cultivated soils

As shown by the example of loamy soils of the European territory of Russia, the geometric parameters of soil structure, along with the agrophysical soil parameters, should be taken into account for the comprehensive assessment of the physical degradation of cultivated soils. Different variants of the geometric transformation of soil structure in the plow horizons are analyzed. The shape and orientation of soil pores in thin sections prepared from undisturbed oriented soil samples are considered to be the main diagnostic indices. A computer-aided analysis of soil pores in thin sections made it possible to distinguish and characterize different levels of the geometric transformation of soil structure upon soil compaction: (a) without the disturbance of the shape and orientation of the aggregates, (b) with the transformation of soil aggregates from the crumb (granular) to the angular blocky shape, (c) with the development of a platy structure characterized by the predominantly horizontal orientation of the pores and aggregates, and (d) the complete disappearance of separate aggregates with the formation of a massive soil structure. The validity of the assessments of the geometric transformation of the soil pore space against the background of a considerable spatial variability in the geometric properties of soil structure in the plow horizon is discussed. The structural-functional specificity of the distinguished levels of the geometric transformation of soil structure is outlined.     

Soil degradation in the tropical lowlands of Santa Cruz,Eastern Bolivia

This paper examines the soil degradation processes that are threatening the productivity of the mechanized annual cropping areas in the Santa Cruz lowlands of tropical eastern Bolivia. The dominant process is that of machinery-induced and natural compaction, which has resulted in an estimated 50 per cent of the soils in the Central Zone being moderately to severely compacted, causing serious root restriction and the loss of both transmission and water-storage pores. Degradation has made the soils increasingly susceptible to moisture stress due to the combined effect of (i) restricted rooting as a result of compaction and the hardsetting characteristics of the soils, (ii) reduced rainfall infiltration due to the loss of transmission pores and surface crusting, and (iii) a decrease in available soil moisture caused by the loss of storage pores, the incorporation of wind-blown fine sand deposits, and soil organic matter losses due to accelerated decomposition rates. The loss of transmission pores has also made the soils more prone to waterlogging in periods of high rainfall. The degradation tendencies of these soils are exacerbated by the greater variability of seasonal rainfall during the last 20 years that has led to a greater frequency or extremely high or extremely low rainfall events than hitherto.     

Microtomographic analysis of pore space in a virgin soddy-podzolic soil

The method of X-ray microtomography was applied to study pore space of a virgin soddy-podzolic soil at the natural soil water content. The morphometric parameters of the pores of more than 100 μm in diameter were determined in the vertically oriented undisturbed soil monoliths (d = 3 cm, h = 3–4 cm) from the genetic horizons of the most differentiated part of the soil profile (the AY, AEL, EL, BEL, BT1, and BТ2 horizons). A tendency for the horizontal orientation of these pores was found in all the horizons, except for the humus (AY) horizon. Isolated vesicular pores of different sizes were abundant in the eluvial part of the profile. Numerous recent and relict phytogenic channels were found in the intraped mass of the BT2 horizon. Differently directed interfaces of structural units in the soil horizons were visualized. Cluster analysis was applied to estimate differences between the genetic horizons with respect to their textures, aggregate sizes, and shapes of pores as seen in vertical two-dimensional X-ray images.     

Shape and intraporosity of topsoil aggregates under maquis and pasture in the Mediteranean region

The clearing of Mediterranean maquis along with the creation of new pasture land has been an important factor of soil and land degradation in the Mediterranean region. The present research compared soil aggregates and their intraporosity in paired pasture/maquis plots in central E Sardinia (Italy), to study the impact of land use change on soil structure. Undisturbed surface horizons were sampled for thin‐section analysis. Aggregate shape was compared and intraporosity was studied for representative aggregates at different depths. Furthermore, the interaction of root activity and grazing under pasture and maquis cover was discussed. The outcomes revealed a complex interplay of trampling and root activity effects. A decrease (–44%) in total voids (regular pores), along with higher aggregate regularity, was observed under pasture in the 0–2 cm layer, and an increase (+261%) in 50–100 μm planar (elongated) pores was determined in the 2–4 cm layer, suggesting a possible surface compaction due to trampling and an increased subsurface fine root activity by the grassland vegetation.     

Effects of tracked vehicles on the morphological and physical properties of tundra soils

The agricultural lands of typic tundra of the Yamal Peninsula in Russia are pastures for reindeer (Rangifer tarandus sibiricus Murr.) herds. Currently, degradation of tundra soil cover is mainly caused by mechanical impacts of tracked vehicles used in construction operations. The objective of this study was to evaluate changes in morphological, micro-structural, and physical properties of Cryozems and Cryogenic peaty soils affected by these tracked vehicles. Soil samples were taken from the surface and underlying horizons before and 5 years after four and 100 passes of tracked vehicles. Surface horizons (0–10 cm) of the undisturbed Cryozems and Cryogenic peaty soils were organogenic. Passage of tracked vehicles caused mixing of these horizons with lower sandy loam and loam mineral horizons. Properties of the organomineral horizons formed in this way differed essentially from those of the surface horizons of the undisturbed soils. Microaggregates were completely disturbed, even after only four passes of tracked vehicles. Large inter-aggregate pores disappeared and thin pores or cracks formed as a result of vehicle-induced mechanical impacts. Humification of plant residues was observed to be faster in the compacted organomineral horizons of disturbed soils compared with undisturbed ones. The organic substances formed in the compacted organomineral horizons readily moved downward within the soil profile or were lost during runoff events. High correlation coefficients of organic carbon content with both specific surface area and water retention showed that the above-mentioned organic substances were hydrophilic. Specific surface area and water retention of the disturbed soils rose with increasing organic carbon content. The results obtained in this study demonstrated a high susceptibility of Cryozems and Cryogenic peaty soils to mechanical impacts.     

THE MEASUREMENT AND CHARACTERISATION OF VOIDS IN SOIL THIN SECTIONS BY IMAGE ANALYSIS. PART II. APPLICATIONS

Image analysis was used to measure and characterise the voids in two sets of soil samples; (i) a surface water gley soil of the Deighton series and (ii) soils from a compaction experiment. The results show that the Deighton soil contains two impervious horizons separated by a much more porous horizon. In all the horizons most of the pore space is due to pores >180μm diam. In the case of the soils from the compaction experiment compaction was shown to change the shape, orientation and size distribution of the pores considerably. The range of measurements demonstrates that image analysis is applicable to several areas of soil research.     

Microfabrics of desert soils of Mongolia

The mineralogical composition of coarse fractions and the specificity of micro- and submicromorphology in the zonal sequence of desert soils of Mongolia (pale brown, gray brown, and extremely arid soils) were studied. A comparative analysis of analytical characteristics and macro- and micromorphological features of these soils made it possible to specify diagnostic criteria of elementary pedogenetic processes in the automorphic desert soils developed from the Quaternary slightly saline alluvial fan deposits. The microfabric of the soil mass near the pores in the crust horizons of desert soils and the microfabric of recent and relict calcite and calcareous-clay coatings on the surface of pebbles were described.     

Macro- and micromorphological features of genetic horizons in a solonetzic soil complex at the Dzhanybek Research Station

The comparative analysis of macro- and microfabrics of soil horizons in a trench crossing a solonetzic soil complex on a virgin plot has shown incomplete correspondence between the macro- and micromorphological features. Solonetzic and solodic horizons and features are differently manifested in different types of soils. The soils of the complex are subjected to continuous transformation dictated by the general trend of the landscape evolution in the Caspian Lowland and by the local changes related to the activity of burrowing animals and fluctuations in the groundwater level. The current trends of evolutionary changes are reflected in the soil microfabrics and salt pedofeatures, whereas more ancient processes are recorded in the properties of the clayey plasma. In the soil of the microlow, the most complete correspondence between the macro- and micromorphological features is observed. At the microlevel, the horizons of this soil resemble the humus-accumulative and metamorphic horizons of dark-colored chernozem-like soils of vast mesodepressions. A variant of the soil evolution within the solonetzic complex is discussed.     

Assessing the impact of Diplocardia ornata on physical and chemical properties of compacted forest soil in microcosms

 The influence of compaction on Diplocardia ornata (Smith) burrowing and casting activities, soil aggregation, and nutrient changes in a forest soil were investigated using pot microcosms. Treatments included two levels each of compaction, organic matter, and earthworms. Both burrowing and casting activities were more abundant in uncompacted soil than in compacted soil. Bulk density decreased in microcosms of compacted soil containing D. ornata from 1.76 g cm^–3 to 1.49 g cm^–3 over the study period. The overall percent of aggregates in the same size classes in compacted soil was less than the percent of aggregates in uncompacted soil. The mean percent of aggregates in earthworm casts for size classes 0.25–1.00 mm was higher for compacted soil than for uncompacted soil. The reverse was true for aggregates in class sizes 2.00–4.00 mm. Soil compaction also affected soil microbial biomass carbon and soil inorganic N concentrations. These results indicate that the burrowing and casting activities of earthworms in compacted forest soils, as in soils of agricultural and pastured lands, can help ameliorate disturbed soils by improving aggregation, reducing bulk density, and increasing nutrient availability. Received: 1 September 1999     

城市功能区、植被类型和利用年限对土壤压实的影响

土地利用会对土壤压实产生影响。本文通过对南京市不同功能区、植被类型和利用年限的土壤进行调查研究,了解这些利用情况对土壤压实的影响程度。结果表明:城郊菜地土壤没有被压实,而城区土壤存在不同程度的压实退化现象;城区内部只有公园土壤与道路绿化带土壤之间的通气孔隙度指标差异显著,其他功能区土壤之间压实指标差异不显著。所以,就压实状况而言,城区内并不存在所谓的功能区之间的差异。植被类型和利用年限对城市土壤的压实都有显著的影响。蔬菜地土壤与自然土壤体积质量和孔隙度相近,为无压实土壤,城区除了树下灌木土壤无压实外,其他植被类型下的土壤均有不同程度的压实退化现象,草坪和裸地土壤压实最为严重。从利用年限看,利用时间少于5年的新土压实程度远远大于利用时间在20年以上老土的压实程度。土壤压实严重与城市建设时的机械压实和草坪建成后的人为践踏密切相关,利用较久的老土壤压实较轻,主要是在无进一步人为践踏情况下,植被生长后根系和土壤生物活动有一定的修复作用。乔木和灌木搭配的修复效果最好。     

Soil compaction caused by harvesting,skidding and wood processing in eucalyptus forests on coarse‐textured tropical soils

Eucalyptus forests play a major role in the world economy, providing raw materials for different purposes. In planted forests, harvest operations performed by heavy machinery may cause severe soil compaction. This study aimed to evaluate the impact of a full‐tree harvesting system in planted eucalyptus forests from Northeastern Brazil. Different soils were evaluated (two Hapludults and one Haplorthod) in two horizons (BA and Bt). We tested different equipment, namely feller buncher, skidder (with traffic intensities of 3, 6, 12 and 16 passes), flail (at different ground‐contact points), grapple saw and loader. The soil physical attributes reflected not only the impact of equipment traffic but also the intrinsic differences between the soils. Bulk density (ranging from 1.36 to 1.80 t m^?3 after trafficking) related well to soil class and horizon. Precompression stress (ranging from 203 to 430 kPa) and degree of compaction (76%–94%) following trafficking were well correlated, while increase in bulk density (reaching a maximum of 20%) related more strongly to soil moisture. A contingency table was constructed with the number of compacted samples and further examined by correspondence analysis. Compaction varied according to soil, horizon and equipment, indicating that machine–soil interactions are very specific and demand detailed research under different conditions. The Haplorthod experienced the greatest amount of compaction, whereas the Hapludult‐2 was more resistant (60% and 25% of compacted samples, respectively). The grapple saw and the skidder at higher traffic intensities (12 and 16 passes) exerted the highest mechanical impacts (81% and 67% of compacted samples, respectively).     

Micromorphology of diagnostic horizons in aridic soils (complementary to the new classification system of soils of Russia)

The micromorphological data on aridic soils are far from numerous; therefore, the information presented here contributes to the development of pedogenetic ideas and characterization of diagnostic horizons and genetic properties in substantive-genetic classification systems. The diversity, functioning, and resilience of aridic soils are basically determined by the properties of their topsoils, which are regarded as recent dynamic formations as opposed to subsoils that formed under a different paleoclimatic environment; topsoil properties are more important for soil classification. Each of the two upper horizons in the new system of soil classification (the light-humus and xero-humus) has the same micromorphological features in different soils; however, in a sequence of soils, some individual micromorphological properties were revealed that indicate increasing aridity. The micromorphological properties of topsoils make it possible to identify the mechanisms of certain phenomena: aeolian deposition, structural rearrangement, the dynamics of secondary carbonates, and cryptosolonetzic manifestations.     

Soil compaction and sealing in Al‐Salmi area,western Kuwait

In the deserts of Kuwait in general and in Al‐Salmi area in particular, soil compaction and sealing are the most significant mechanisms of land degradation. In the present study, soil compaction and sealing in the Al‐Salmi area are assessed. The study is based on analysis of satellite images and aerial photographs, besides field measurements and laboratory investigations. Based on this study, a recent map is prepared for the concerned area. It shows three different soil classes. These are highly compacted (8\8 per cent), slightly compacted (1\7 per cent), and almost non‐compacted or natural (89\5 per cent). Soil compaction in Al‐Salmi area causes adverse changes in soil physical properties, e.g. infiltration rate, bulk density and soil strength. The infiltration capacity of the compacted soils has decreased by 18\46 to 91\96 per cent in comparison with non‐compacted soils. The bulk density for the compacted soil varies between 1\6 and 1\7 g cm⁻³, whereas it varies between 1\2 and 1\35 g cm⁻³ in the non‐compacted soils, that is an increased of 29\97 per cent. In some sites, the physical properties show small or no difference between compacted and natural soils due to the effect of soil sealing (crustation). Copyright © 2000 John Wiley & Sons, Ltd.     

Lessivage and its relation to the hydrological regime of soils

By the examples of four typical catenas in the East European Plain, the role of lessivage in the development of automorphic and hydromorphic loamy and clayey soils with light-colored acid eluvial horizons and with different degrees of gleyzation has been studied. It is found that characteristic features of lessivage are often observed in the soils without hydrological barriers hampering or preventing the vertical migration of soil water and mass transfer processes. The hydrological barriers may be represented by the shallow horizons of temporarily perched water, or by the ascending capillary fringe of the ground water, or by the water-saturated horizons, in which the volume of free pores does not exceed 2–4%. It is shown that light-colored acid eluvial horizons may be formed in the profiles of loamy and clayey soils without any signs of lessivage. The development of strongly gleyed soils (gleyed soddy-podzolic soils and pseudogley soils (Stagnosols)) is not related to colmatage (silting of their illuvial horizons through lessivage); it is conditioned by the actual hydrological regime of these soils. The role of lessivage, podzolization, and gleyzation in the development of clay-differentiated soils is discussed.     

Artificial pores attract barley roots and can reduce artifacts of pot experiments

Soil compaction is a severe agricultural problem. It is characterized by an increased resistance to root penetration and by a decreased amount of porosity in the soil. Until today it is not clear whether crop roots are able to actively detect remaining pores in compacted soil. Moreover, little is known about the capability of roots to leave pores again if the mechanical resistance of the bulk soil allows so. The aim of this study was to investigate the root growth response of spring barley (Hordeum vulgare L. cv. Ascona) in different configurations of a compacted loamy soil containing pores. The three‐dimensional configurations of the root systems from three well watered and fertilized treatments were analyzed with X‐ray computed tomography. All soil‐filled cylindrical plastic pots (diameter: 60 mm, height: 210 mm) contained loose topsoil but differed in subsoil structure. In treatment ‘Loose' [L] the pots were entirely filled with loose soil. Treatment ‘Lower part compacted' [C] contained compacted soil in the lower part of the pots. Likewise, treatment ‘Pores' [P] contained compacted soil in the lower part too, but here 16 artificial pores (1 mm diameter) were generated in the central part of the compacted subsoil zone. Comparison of the two treatments with compacted soil [C] and [P] showed that the roots were able to detect pores. However, the roots frequently grew across the pores or left the pores again after having grown into them, leading to a significantly higher fraction of roots exploring the compacted soil in the treatment with pores compared to the treatment without pores. These findings are useful for designing controlled experiments in pots of limited size that can mimic root growth in relatively complex soil structures which are more similar to field situations than usual pot experiments.     

湿润速度和累积降雨对土壤表面结皮发育的影响

土壤表面强度和微结构显微照片是研究表土结皮的重要指标和直接表征。以两种典型的土壤(垆土和黑土)为研究对象,采用2mmh-1(慢速)和50mmh-1(快速)两种速度湿润后进行雨强为60mmh-1的降雨,研究不同湿润速度和累积降雨对结皮发育的影响。结果表明:湿润速度对垆土结皮发育过程的影响不明显,土壤表面强度主要由累积降雨打击夯实引起;快速湿润对黑土结皮发育有显著的影响,慢速湿润后黑土在60min降雨过程中没有明显的结皮,累积降雨的打击起次要作用;湿润速度和累积降雨的对结皮发育的影响取决于土壤团聚体稳定性。     

The effect of compaction on soil electrical resistivity: a laboratory investigation

Among the geophysical tools used in soil science, electrical methods are considered as potentially useful to characterize soil compaction intensity. A laboratory investigation was undertaken on agricultural and forest soils in order to study the impact of compaction on bulk soil electrical resistivity. Samples taken from four different types of loamy soils were compacted at three bulk densities (1.1, 1.3 and 1.6 g cm⁻³). Bulk soil resistivity was measured at each compacted state for gravimetric water contents ranging from 0.10 to 0.50 g g⁻¹. A specific experimental procedure allowed the control of the water‐filling of the intra‐aggregate pores and the inter‐aggregate pores. Soil resistivity decreased significantly with increase in density and typically for gravimetric water contents less than 0.25 g g⁻¹. The decrease was more pronounced for the drier soils, indicating the strong impact of the surface conductance, especially in agricultural soils. The experimental data were in good agreement with simulated values given by the petro‐physical model of Waxman‐Smits (1968) , at least for water saturation greater than 0.3. The analysis of the petro‐physical parameters derived from the experimental data suggested that: (i) the electrical tortuosity of the loamy agricultural soil was significantly affected by compaction and (ii) the forest soil had a singular microstructure from an electrical point of view and had isolated conductive zones associated with clay embedded in a poorly conductive medium comprised mainly of soil solution and quartz grains. Our results provide the phenomenological basis for assessing, in the field, the relationship between soil electrical resistivity and compaction intensity.     

Higher levels of description—approaches to the micromorphological characterisation of Russian soils

Several attempts were made in the past to identify high-level soil microfabrics, following the ideas of Kubiëna. They resulted in proposals to identify specific fabric types, soil materials, somas, formations, or morphotypes, based on the combinations of micromorphological characteristics of the studied horizons of soils. These units present complex (integrated, typical, and central) micromorphological images of soil horizons or materials. Using the available information on Russian soils, the author defined the “micromorphotypes” of soil horizons by illustrating this approach by two examples of simple and complicated genetic horizons. Emphasis was put on genetic and diagnostic aspects of micromorphological interpretations, which is traditional for Russian micromorphological studies. Moreover, the definition of “micromorphotypes” was derived from the ideas of diagnostic horizons, which serve as a base for the new Russian soil classification system. Examples of “micromorphotypes” are discussed for a Chernozem and major mineral horizons of loamy soils with textural profile (correlated with Albeluvisols in the WRB system). They illustrate the morphogenetic principles applied, and also bring to light some problems concerning the choice and hierarchy of criteria used for a number of soils.This “micromorphotypes” approach may contribute to the diagnostics of horizons for soil classification, for detection of human impacts, and for the identification of paleosols and their diagenetic changes. To facilitate contacts with nonprofessionals in micromorphology, a simple terminology and a priority of pedogenic principles seem to be preferable.     

Soil degradation in Kabd area,southwestern Kuwait City

Adverse environmental impacts of human activities are the main causes of soil degradation in the desert of Kuwait in general, and in Kabd area in particular. In this study, assessment of soil degradation in open and protected sites has been carried out using field measurements and laboratory investigations. The overall status of vegetation is nearly twice as low in vegetation cover in the open sites than in the protected ones due to overgrazing and off‐road transport. Compaction of soil due to pressure exerted on the soil by vehicles led to a significant reduction in its porosity, permeability and infiltration capacity. The average infiltration rate of the compacted soils is 51 per cent lower than that of the non‐compacted soils. The bulk density of the non‐compacted soils is 3.4 per cent lower than that of compacted soil. The average topsoil resistance of compacted soils has increased by 83 per cent in comparison with non‐compacted soil. Using the least squares method a relation between infiltration rate (IR) and penetration resistance (PR) of the topsoil for the study areas is found (i.e. IR = −0.148 PR + 1.85 with R² = 25 per cent). Soil strength within the soil profile shows maximum penetration resistance readings at 11.5 cm depth in average in compacted soils, while it shows maximum readings at 34.6 cm depth in average in non‐compacted soils. The adverse changes in the chemical properties due to soil compaction is also investigated. A restoration plan is needed in order to reduce land degradation. Copyright © 2002 John Wiley & Sons, Ltd.