The influence of the water content of soil pastes on their viscosity is studied using vibrational viscometry, and the variable viscosity is explained by the structural organization of soil humic ...substances (HSs). The viscosity of pastes prepared from sod-podzolic soil increases to 4000–4200 mPa s with a decreasing water content of <36% and further remains almost the same. This contradicts the current views on the viscosity of suspensions, which should continuously increase with decreasing water content. This situation is explained by the fact that, in addition to water soil particles (aggregates and microaggregates), the soil paste contains one more component of supramolecular formations (SFs) from soil HSs, which could separate from soil gels and transit to disperse conditions. According to the literature data, the HS SFs are present in soils as fractal clusters (F-clusters) of particles–molecules. Because of the high stability of F-clusters, we can suggest the presence of soil particles in pastes sliding along F-clusters, whereas the change in the thickness of a sliding F-cluster layer has a minor effect on the viscosity of soil pastes. Our data on the viscosity of soil pastes confirm the significance of F-clusters for the formation of soil properties.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, IZUM, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
During studying water stability of soils, spherical particles of several hundred nanometers in size were found to be released from the soil into the water at capillary contact of soils with water. ...Such particles were shown to pass into water from any humus-containing objects—soils, peats, humic acids, humates, and fulvic acids. Elemental microanalysis of such particles released from soddy-podzolic soil showed that they consist mainly of organic matter. These particles represent previously detected supramolecular formations (SF) from specific organic matter of soils. Humic substances of soils are known to be fractally organized, and in water they exist as fractal clusters of several hundred nanometers in size (F-clusters) consisting of particles–molecules of humic substances of about 10 nm in size. This allowed us to assume that the supramolecular formations released from humus-containing samples are F-clusters. Based on the high stability of supramolecular formations of humic substances to decomposition into particles–molecules, it follows that humic substances in soils should have a fractal–cluster organization.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
The influence of the contact of chernozem, soddy–podzolic, and gray forest soil aggregates with water on their water stability has been studied. An increase in the contact time of soil aggregates ...with water leads to a gradual decrease in their water stability. Based on the verified salt solution effect on the water stability of soil aggregates, the water stability of the loss of aggregates in contact with water is not directly proportional to the disjoining pressure. When soil aggregates come into contact with water, fractal clusters of humus particles (F-clusters) are isolated from them. It is suggested that the F-clusters that the soil gel is based on control the physical basis of the water stability of the soil.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, IZUM, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
In modern soil physics soil stability as a concept is divided into two directions, namely water stability and mechanical resistance to compression and wedging. Both soil properties in water-saturated ...soil are based on the rupture of interaggregate interparticle bonds, however, no standard of physically based parameters have been proposed to characterize the aggregate stability. The purpose of the article is to substantiate the physical concept of stability of soil aggregates and to propose a single methodological method for quantifying stability as a normative soil characteristic. A high-performance method has been developed based on the dissection of linearly arranged water-saturated aggregates with blades under controlled load. The main stages of the technique are vacuuming of aggregates to eliminate the uncontrolled influence of trapped air, saturation of aggregates with water in vacuum, and subsequent determination of the aggregate stability to penetration of blades. Experimental stability values (mN/aggregate) were obtained for 17 soils, which made it possible to form normative ranges for arable loamy soils, namely 17–19, 27–29, and 34–37 mN/aggregate for soddy-podzolic, gray forest soils, and chernozem, respectively, and a number of other soils, which makes it possible to apply the obtained value as a soil characteristic of the aggregate stability. The possibility of using the stability values as a methodological basis for monitoring soil stability and degradation and for quantitative directions for assessing of physical characteristics of soil aggregates (firstly, their main parameter—stability) is discussed. Taking into account the highly correlative dependence of the proposed stability characteristic on the water stability values obtained by the Savvinov method (>85%) and the high performance of the stability determination method (the proposed method is about 20 times more productive than the Savvinov method), the possibilities of using the method and the obtained values of the stability of aggregates as a general physical characteristic and a separate one for quantifying water stability are discussed.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
It is common to consider the experimental soil physics results from the standpoint of a three-phase soil model. Along with the three-phase model, a gel model of soils is used. These models are based ...on different principles: in the three-phase model, solid phase constancy and liquid mobility; in the gel model, the ability of soil gels to swell, harden, and reduce water mobility. The purpose of this work is to assess the applicability of three-phase and gel soil models to analyzing the study results of some physical properties of soils. The studies were carried out with the zonal soil series: sod–podzolic, gray forest, chernozem, and chestnut soils. The following methods were used in this work: vibration viscometry, laser diffractometry, and electrical resistivity of soils. Unexpected results were obtained in the study of the soil’s physical properties. Firstly, the curve of the relationship between the moisture content of soil samples and the viscosity of pastes prepared from them reached the maximum at the point of limited availability of water (PLAW). Secondly, under the increased mechanical action on soil pastes, the particle size increased rather than decreased in them. Thirdly, the soil electrical resistivity–moisture relationship maintains a uniform course in the PLAW area. Meanwhile, at this water content, the continuous liquid phase framework providing moisture and electrical conductivity disappears in the soils. Fourthly, moist soils dry out in a desiccator over water. It is not possible to explain these results from the standpoint of the three-phase soil model generally accepted in soil science. For this reason, the gel model of soils was used to analyze and explain all the results obtained.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, IZUM, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Based on an analysis of the presumed mechanisms of the hysteresis of the water retention curve (WRC) for soil drying and wetting, as well as the ideas about the nanostructural organization of soils, ...a conclusion is made that the hysteresis can be caused either by stable (non-colloidal particles) or labile (gels) parts of the solid phase in soils. Due to the fact that until recently the main attention has been focused on study of the effect of the stable solid phase of soils on the hysteresis of the WRC, it is proposed to investigate the effect of soil gels on hysteresis. For this purpose, the effect of the moisture content of soil samples prepared by drying and wetting on the initial viscosity of soil pastes is studied. It has been established that a well-defined hysteresis is observed for the samples of all soil types studied. To explain the hysteresis, two mechanisms based on changes in soil gels in the wetting–drying processes are proposed. One of them is based on the slowness of swelling and shrinkage of soil gels when they absorb and release water. The second is based on the greater hydrophobicity of the surface of gels containing less water, and water slippage on hydrophobic areas of the surface with a decrease in the viscosity of pastes. Thus, the studies conducted have shown that hysteresis phenomena in soils are caused by soil gels and their changes during drying and wetting of soils.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, IZUM, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Humic substances influence a number of soil properties: structure, cation exchange capacity, water retention capacity, etc. At the same time, in soils and solutions, humic substances exist not in the ...form of individual molecules, but in the form of supramolecular formations having a fractal cluster organization (F-clusters). Consequently, F-clusters should exert their influence on soil properties. As F-clusters are tightly interconnected, to assess their influence on soil properties it is necessary to separate them. This can be done by mechanical activation—increasing the reactivity (activity) of substances during their mechanical treatment. We studied the influence of mechanical activation on some soil properties and on the development of plants in activated soils. It has been shown that the water retention capacity of soil samples from the main types of zonal soils increases by up to 35% of the initial value under the impact of mechanical activation. This can be explained from the standpoint of a decrease in the mobility of gravitational water by F-clusters in macrocapillaries. The optical density of water extracts from chernozem increased by 75% and the viscosity of soil pastes increased by 57% due to an increase in the number of F-clusters in the soil solution. Activated soils stimulated the germination of wheat seeds by 26%. This effect may be associated with the formation of films of F-clusters on the surface of seeds, which fix soil allelotoxins that slow down seed development.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Based on earlier study results, the drying process changes the soil properties and, in particular, the characteristic features of a specific soil organic material such as a humic substance (HS). HS ...is the basis of soil organomineral gels that cover and bind soil particles. When water is removed from soil, gels are subjected to hydrophobization and compression resulting in changes in properties of soil samples. The recovery of soil gels of air-dried samples should reduce the discrepancy between the study data obtained on the soil properties of dried and non-dried soil samples. The study objective is to find ways to recover the structure of soil gels. Samples of six soil types were studied. Vibration viscometry, laser diffractometry, scanning electron microscopy (SEM), photocolorimetry, and conductometry were used in this work. The drying of soil samples increases the size of supramolecular formations (SMFs) in the soil and reduces the soil paste viscosity, a parameter characterizing the structure and the ability of gels to swell. To recover the structure of soil gels, it is proposed to reduce the size of SMFs from HSs to the initial level. SMFs of air-dried samples were separated by soil moistening and subsequent treatment with various temperatures, by ultrasound, and by freezing. Based on the SEM data, heating and ultrasound treatment do not reduce, but enlarge SMFs. Humidification of air-dried soils, exposure to moisture for two weeks, and subsequent freezing bring the paste viscosity of a number of studied soils closer to the condition of samples that were not dried. This process is due to the return of SMFs to size values of the initial soils, as evidenced by the laser diffractometer data on the suspended particle size distribution. Hence, a method for recovery of gel structures in dried soils to the initial state is proposed.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, IZUM, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
The opinion exists that water stability is provided by hydrophobic bonds between organic soil particles; however, there are works in which the main role in the occurrence of this property is assigned ...to the presence of hydrophilic organic substances in soils. The goal of this study is to clarify the nature of the bonds (hydrophilic or hydrophobic) that ensure the water stability of soils. We used samples of sod-podzolic and gray forest soils, as well as leached chernozem. Experiments to assess water stability were carried out using the method of “blades.” It is based on the dissection of linearly arranged aggregates, which were preliminarily moistened in vacuum to values close to saturation. The energy of hydrophobic bonds depends on the temperature; therefore, the influence of temperature on the value of the determined water stability was studied. Experiments showed that, as the temperature increases, the water stability of aggregates stored in the wet state increases from the moment of selection and decreases as the temperature increases. This indicates the leading role of hydrophobic bonds in the formation of water stability. As for the samples dried to an air-dry state, moistened again, and kept wet for more than two weeks, no temperature dependence of the water stability has been found. Taking into account that the strength of hydrophobic bonds increases with increasing temperature, while that of hydrophilic bonds decreases, the obtained data immutability of water stability can be explained if we assume the joint participation both hydrophobic and hydrophilic bonds in water stability of soil samples that have passed through the stage of drying to an air-dry state. In fact, these results indicate a strong change in the structural organization of soils during drying.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, IZUM, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
