It is known that tensile strength of soil samples is by three orders of magnitude greater than the shear stresses on the bottom of slope streams responsible for the detachment and transport of soil particles by water current. C.E. Mirtskhulava believed that detachment of soil particles by water current occurs due to the fatigue destruction of bonds between soil particles.Taking this fact into account, tensile strength is lower by two orders of magnitude. M.A. Nearing had an opinion that detachment of soil particles occurs in the points of separation of vortices from the bottom of the stream, where the shear stress is by two orders of magnitude higher than the average. These approaches did not explain overcoming by slope streams of the cohesion forces between soil particles. Studies of the influence of water temperature on the washout rate of model samples have shown that the soil erosion is highly dependent on the water temperature, which is close to the Van’t Hoff’s rule. This means that destruction of bonds between soil particles is probably the result of interaction between the soil solid phase and water molecules. Experiments have also shown that destruction of bonds between soil particles in the sample of chernozem monoaggregate soil occurs under a layer of still water. Upon the start of the water flow, particles that lost bond with the rest of the soil body immediately break away. The number of particles with disrupted bonds grows with the duration of the sample exposure to still water, although with some flattening. Experiments confirm the validity of the hypothesis of non-hydraulic nature of forces that disrupt inter-aggregate bonds during water erosion.

Under study was the possible assessment of soil infiltration capacity by using a portable rainfall simulator to irrigate a small area and avoid the development of rill erosion. For soil infiltration capacity an equation has been suggested, including erosion rain index AI as a criterion of similarity. The equation was verified for natural rainfalls (for catchments and runoff plots) and for artificial rain (for a runoff plot 5 m long and 5 m² in size). To evaluate the soil infiltration capacity, the small runoff plots can be used, on which no rill erosion doesn’t take place. To verify this affirmation two experiments were conducted. In the first experiment a large rainfall simulator and a runoff plot 3 m long having the area 3 m² in the field were used. Rill erosion took place on this runoff plot. In the second experiment a portable rainfall simulator and a runoff plot shaped as a circle with the area 0.05 m² were used (rill erosion did not take place). The experiment was conducted in the laboratory by using the soil monoliths taken in the same field. For both rainfall simulators the raindrops were of the same size, they fell down from the same height, the rainfall intensity was constant, but the values of these parameters seemed to be different. In experiments a close dependence between the soil infiltration capacity and the index AI was established. The use of the portable rainfall simulator requires expenses to a lesser extent.

The soils are distinguished by the presence and the profile distribution pattern of such pedogenic parameters as the organic matter content, available pedofeatures, structural state of the soil mass, etc. They differ in the organization of the pore space throughout the soil profile as well. Under discussion are results of computer micromorphometric analysis of fine macropores d = 0.2-2.0 mm in thin sections of vertical orientation from samples taken in genetic horizons of podzolic, soddy podzolic, gray forest soils and chernozems at the territory of European Russia. The profile changes in voids were analyzed using the most informative morphometric parameters such as the total area of the studied voids in thin sections, the content of fissure-like voids and those of vertical and/or horizontal orientation. The soil types under study showed differences in profile distribution of the above parameters. By analogy with the profile of carbonates, salts, organic matter it is proposed to recognize diagnostic profiles of the pore space represented as a system of voids in genetic horizons of the soil profile. Empiric profiles of the pore space reveal a great diversity. The most complicated organization of the pore space is inherent to soddy podzolic soils, the most simple “smoothed” profiles are characteristic of typical chernozems. The expert qualitative typization showed that the eluvial-illuvial and accumulative-eluvial-illuvial types are dominant among the studied empiric profiles of the pore space (42 and 30% respectively), what is explained by prevailing texture-differentiated soils. On the other hand, it makes possible to use the profile of the pore space as a diagnostic parameter of soils and soil formation processes.

A short review of literature sources is presented to characterize the eroded soils according to their humus content. Traditional diagnostic indicators of the soil erodibility level based upon the humus status are the following: (1) decrease in the thickness of humus horizons in eroded soils in percentage of that in uneroded soil (standard); (2) decline in the humus storage in the eroded soil profile in percentage of that in uneroded soil (standard). It is worth emphasizing that the choice of the uneroded soil standard is a rather labor-consuming study in field and assumes an expert (subjective) character that is highly dependent on the soil scientist’s skill. It is shown that the main shortcomings of the available gradation for eroded soils consist in the absence of approaches to give their objective estimate and recommendations for permissible levels of soil erodibility taking into complete account the humus content in these soils. In the Russian Federation there is a gradation of arable soils (including chernozems) according to the humus content in the plough horizon. It contains four classes (less than the humus minimum, low, moderate and high humus content). In this paper it is recommended to give the gradation of eroded soils with the minimal humus content. The level of chernozem erodibility should be estimated as based upon the minimal and critical humus content. The minimal humus content is interpreted by Kërshens, whereas the critical humus content - by Kiryushin and Ganzhara. A gradation scale of soil erodibility is presented to estimate its permissible, non-permissible and critical levels. It is exemplified by the gradation of chernozem soils in Russia and Germany.

The soil organic matter is one of the factors affecting the phosphate ionic sorption of soils. Of special interest is the study of sorption characteristics of organo-mineral relationship products in soil. The organic-clay (clay fractions) and organic (fine fractions) complexes play the most important role in developing the soil phosphate regime. Under study was the phosphate state in plough horizons of erosion-degraded agro soddy-podzolic soils as based upon the parameters of the phosphate-ionic sorption in different components of the organic matter. The organic and organomineral fractions of plough horizons in soils that were not subjected to water erosion are characterized by a high level of phosphorus mobility and the capacity to provide a constant amount of phosphates available for plants (P_mob is 17.95±2.06 mg/kg of soil), the low sorption capacity to phosphate-ions (P_sorp is 96.06±0.53 mg/kg of soil). Agro-ecological peculiar features of eroded soils are the increased sorption of phosphate-ion (P_sorp becomes higher by more than 2 times) and the low level of available phosphorus (P_mob is declined almost by 2 times) as compared to those in uneroded soils. The processes of sediment accumulation promote some improving the soil sorption parameters, what is manifested in increasing the amount of mobile phosphorus in the soil solution and in decreasing the phosphorus sorption by the soil solid phase. In this case P_mob is increasing by more than 20% in washed-out soils, whereas P_sorp becomes decreased by 1%. A set of parameters for the phosphate-ionic sorption of organomineral components in the studied soils with different elementary soil structures may serve as an informative system for estimating the phosphate regime in erosion-degraded agro soddy-podzolic soils.

Molecular-biological methods permitted to study the structure of the microbial community in the profile of dark-gray soil (Luvic Retic Greyzemic Phaeozem) in Kashira district of the Moscow region. Microorganisms playing an important role in transformation of the soil organic matter are mainly concentrated in the topsoil and the major microbiological studies are related to this part of the soil profile. However, the study of the microbial community in the lower soil horizons is not only of theoretical but also practical interest in view of increasing the intensity of erosion processes. The method of quantitative polymerase chain reaction was used to estimate the DNA quantity of bacteria, archespores and micromycetes in horizons of the above soil. Under study was also the crotovina material at a depth of 80 cm. The highest DNA quantity of bacteria and archespores proved to be in the upper humus-accumulative horizon (9.6 × 10⁸ and 9 × 10⁷ copy/g of soil respectively). Their quantity was decreased downwards the profile, what is connected with changes in the physic-chemical conditions of soil. DNA of micromycetes was evenly distributed throughout the soil profile (5.4-9.4 × 10⁷ copy/g). In the crotovina material the DNA content of different microorganisms groups was close to that in lower mineral soil horizons. This may be explained by water infiltration through the crotovina accompanying by eluviation of microorganisms in the period of soil wetting. The factors affecting the DNA amount of microorganisms are elementary soil processes including the biogenic-accumulative process in the upper soil horizons, clay-illuvial and humus-illuvial processes in the lower horizons of the dark-gray soil.

Peculiar features for the formation of structural elements (clasters) and regularities in their growth have been identified by precipitating the clay fractions extracted from samples of gray forest soils in water suspensions with the view of determining the mechanism responsible for the formation of the soil microstructure under the influence of temporary wetting-drying processes. Under use were suspensions of soil samples (<1 mkm) prepared by traditional methods for the particle-size distribution and microaggregate analyses and preliminary dried (1-2 times). One suspension drop taken by a pipette from the middle part of the test-tube was placed on the laboratory glass of 1x1 cm size. After the water evaporation (48 hours) this procedure was repeated once more and 14 samples were prepared including 7 samples with the clay precipitation from one suspension drop and 7 samples from two suspension drops. Then the raster electronic microscope REMJEOL 6060A was used for scanning of these preparations. The mathematical processing permitted to identify tend towards increasing the accumulation of fine-sized particles, their quantity and decreasing the distance between the formed clasters in the course of their precipitation. When developing clasters of the second order (cyclic precipitation) it seemed possible to establish that the distribution density of structural elements is sharply increased and newly formed clasters can lead to irreversible changes in the soil microstructure and the aggregate destruction. Only the humus promotes weakening these processes. In samples of parent materials such changes in the size of claster doesn’t occur under identical conditions.