Том 50, № 2 (2017)

This paper considers regularities governing the formation of automorphic tundra soils on glacial loamy deposits containing relict organic matter mainly represented by very fine plant detritus. Drainage, microtopography, and cryoturbation activity are the major controls of the development of these soils. With an increase in drainage, the following pedogenetic trend is observed on the surface of yedoma (Ice Сomplex) areas: gleyzem–cryozem–cryometamorphic soil. The climate change in the Holocene induced quick transformation of topography and general landscape situation and promoted formation and development of cryogenic soil complexes in the considered territory. Upon the low intensity of pedogenesis, the features and properties of previous soil formation stages are often preserved in the soil profiles; these are: gleyzation, peat accumulation, and cryoturbation.

Morphogenetic features of soils on the selected plots in the Cat Tien National Park in southern Vietnam have been studied with the use of a set of morphological, analytical, and instrumental methods. The lithological factor and topographic position play the leading role in the development of the particular genetic soil features. The soils can be subdivided into four groups according to these factors. The soils developing from volcanic deposits with a predominance of tephra can be classified as thin clayey brown tropical soils (Dystric Skeletic Rhodic Cambisols (Clayic)), and the soils developed from less weathered colluvial derivatives of basalts with some admixture of tephra can be classified as dark-humus clayey tropical soils (Skeletic Greyzemic Umbrisols (Clayic)). Very poor soils developed from the eluvium of argillites are classified as thin weakly developed clayey tropical soils (Dystric Regosols (Clayic)). The soils forming from the alluvial sediments of different textures are classified as alluvial loamy sandy soils (Dystric Fluvisols (Arenic, Drainic)) and as alluvial clay loamy soils (Eutric Fluvisols (Episiltic, Endoclayic)).

Soils sensu stricto are absent on Mars; most probably, they have never been formed there, because, up to now, we have no evidence of the presence of life, either relict or recent, on this planet. Numerous references to “Martian soils” in scientific literature concern loose substrates rather than Dokuchaev’s soils. In this context, surface bodies on Mars can be described using the concept of planetary shells, or exons. Exons can be subdivided into sitons formed via in situ transformation of parent material, transons formed in the course of lateral transportation and deposition of substances, and transsitons formed by the combination of both in situ and lateral processes. Among Martian exons, transons predominate. They represent loose sediments of mainly eolian genesis related to extremely strong winds. Soil-like bodies (soloids) on Mars are represented by sitons and transsitons. These are abiotic formations having the profiles differentiated by the contents of iron oxides, soluble salts, and clay minerals and mainly formed in the presence of liquid water during the paleohumid eras of Mars evolution more than 2.5/3 billion years ago. True deep sitons (Martian weathering mantles) could only be formed under the impact of long-term weathering on stable surfaces during humid eras. Then, they were either buried by later deposited sediments, or eroded. Up to now, such objects have not been discovered on Mars.

Regularities of extracting humic acids from different soil types (soddy-podzolic soil, gray forest soil, and all chernozem subtypes) with sodium pyrophosphate solutions at different pH values (from 5 to 13) have been studied. It is found that, regardless of soil type, the process occurs in two stages through the dissociation of carboxylic groups and phenolic hydroxyls, each of which can be described by a logistic function. Parameters of the logistic equations approximating the extraction of humic acids from soils at different pH values are independent of the content and composition of humus in soils. Changes in the optical density of humic acids extracted from soils using sodium pyrophosphate solutions with different pH values are described in the first approximation by the Gaussian function. The optically densest humic acids are extracted using sodium pyrophosphate solutions at pH 10. Therefore, it is proposed to use an extract with pH 10 for the characterization of organic matter with the maximum possible degree of humification in the given soil.

Changes in the structural state of migrational-mycelial (typical) chernozems (Haplic Chernozems (Clayic, Aric, Pachic)) as dependent on the duration of their cultivation (from 20 to 120 years) are considered. Field studies were performed in 2013 on the fields of the Dokuchaev Research Institute of Agriculture in the Central Chernozemic Region of Russia (the Kamennaya Steppe area) used for growing cereals and row crops in rotation. The study showed that the most intensive degradation of the structure of chernozems takes place during the first two decades of their agricultural use. The maximum transformation of the soil structure is observed in the upper 10 cm, as this layer is subjected to the most frequent and intense mechanical impacts. The rate of structural degradation decreases with time until the equilibrium between disaggregation and aggregation processes is reached. The time required for this largely depends on the applied crop rotation systems and agrotechnologies. In this context, flexible assessment scales for the structural state of agrochernozems under conditions of different farming systems should be developed in order to perform monitoring of the physical properties of cultivated chernozems for their long-term efficient and ecologically sustainable use. Despite general disintegration and destruction of granular aggregates, the structural state of agrochernozems in the Kamennaya Steppe area remains sufficiently good even on the old-cultivated (120 yrs.) fields.

The size and structure of microbial pool in light chestnut paleosols and paleosolonetz buried under kurgans of the Middle Bronze Age 4600–4500 years ago (the burial mound heights are 45–173 cm), as well as in recent analogues in the desert-steppe zone (Western Ergeni, Salo-Manych Ridge), have been studied. In paleosol profiles, the living microbial biomass estimated from the content of phospholipids varies from 35 to 258% of the present-day value; the active biomass (responsive to glucose addition) in paleosols is 1‒3 orders of magnitude lower than in recent analogues. The content of soil phospholipids is recalculated to that of microbial carbon, and its share in the total soil organic carbon is determined: it is 4.5–7.0% in recent soils and up to three times higher in the remained organic carbon of paleosols. The stability of microbial communities in the B1 horizon of paleosols is 1.3–2.2 times higher than in the upper horizon; in recent soils, it has a tendency to a decrease. The share of microorganisms feeding on plant residues in the ecological–trophic structure of paleosol microbial communities is higher by 23–35% and their index of oligotrophy is 3–5 times lower than in recent analogues. The size of microbial pool and its structure indicate a significantly higher input of plant residues into soils 4600–4500 years ago than in the recent time, which is related to the increase in atmospheric humidity in the studied zone. However, the occurrence depths of salt accumulations in profiles of the studied soils contradict this supposition. A short-term trend of increase in climate humidity is supposed, as indicated by microbial parameters (the most sensitive soil characteristics) or changes in the annual variation of precipitation (its increase in the warm season) during the construction of the mounds under study.

The evolution of Russian concepts concerning the assessment of soil suitability for cultivation in relation to several campaigns on large-scale plowing of virgin steppe soils is examined. The major problems of agricultural land use in steppe areas—preservation of rainfed farming in the regions with increasing climatic risks, underestimation of the potential of arable lands in land cadaster assessments, and much lower factual yields in comparison with potential yields—are considered. It is suggested that the assessments of arable lands should be performed on the basis of the soil–ecological index (SEI) developed by I. Karmanov with further conversion of SEI values into nominal monetary values. Under conditions of land reforms and economic reforms, it is important to determine suitability of steppe chernozems for plowing and economic feasibility of their use for crop growing in dependence on macroeconomic parameters. This should support decisions on optimization of land use in the steppe zone on the basis of the principles suggested by V. Dokuchaev. The developed approach for assessing soil suitability for cultivation was tested in the subzone of herbaceous–fescue–feather grass steppes in the Cis-Ural part of Orenburg oblast and used for the assessment of soil suitability for cultivation in the southern and southeastern regions of Orenburg oblast.

Experiments on small (about 10 m in length) runoff plots on slopes of 1°–3° subjected to sprinkler irrigation in the southern Cis-Ural forest-steppe region showed that the formation of surface runoff is controlled by the intensity and character (intermittence) of sprinkler irrigation, its duration, and the state of the soil surface. On the clay-illuvial moderately leached agrochernozem, the surface runoff is developed after 14‒20 h of irrigation imitating heavy rain (180–210 mm rainfall), after 15 min (24 mm) under shower, and after 10 min (23 mm) under heavy shower. Runoff appeared on the plowed plots unprotected by plants after 100–140 mm of heavy rainfall 6 h earlier than on the fallow plot; in the case of shower and heavy shower on the unprotected plot, it appeared virtually immediately. Turbidity of runoff flows gradually increased after the beginning of runoff under heavy rain and sharply increased under heavy shower. After reaching its maximum, it decreased. The contents of fine fractions, humus, and nutrients in the solid runoff (drift) were higher under lower rain intensity (heavy rain) than under showers and heavy showers; they were higher in all the drifts than in the soil on the adjacent slope. Long (about 24 h) continuous artificial heavy rain (0.17–0.22 mm/min) caused slight soil compaction and some improvement of the structure of the surface soil layer both on the fallow plots and on the plowed plots.