Volume 52, Nº 3 (2019)

The current state of knowledge on the problems of soil memory is highlighted. A brief review of recent publications concerning soils as information systems, soil behavior in time and space, and reconstruction of the environment based on soil records is given. Theoretical basics of the concept of soil memory as a soil capacity to record the environmental factors and soil forming processes in a set of stable features in the solid phase of the soil body are discussed. Mechanisms of recording, accumulation, and storage of this information, its particular carriers, and methods of their study are considered. Two major models of soil memory and distribution of records in a soil profile in response to evolutionary changes in the environment and soil are suggested in dependence on an increase or a decrease in the pedogenetic potential of climate and biota. A notion of geosystem memory is introduced. The blocks of geosystem memory are discussed in a hierarchy from a subsystem level to a level of particular discrete objects. Environmental proxy indicators for each block of geosystem memory are listed. Further prospects for the development of the concept of soil memory are seen in widening of a set of methods applied to study the solid-phase soil matrix and in linking the studies of particular components and elements of a soil body with its hierarchical morphogenetic analysis.

The data of experimental studies on the postpyrogenic dynamics of the litter in mountain taiga cedar (Pinus sibirica), pine (Pinus sylvestris) and subtaiga forest-steppe pine (Pinus sylvestris) forests in the Baikal region are analyzed. Ground fires prevailing in this region transform the surface organic diagnostic horizons of soils and result in the formation of new pyrogenic organic horizons (Opir, OLpir, OL/Opir, OApir). The adverse impact of ground fires on the thickness, reserves, moisture capacity and fractional composition of forest litters is shown. The data on the chemical ash composition of litters, as well as the content of mobile microelement compounds is also given. The tendency of reducing the concentration of mobile elements in the organic horizons of soils from the taiga Siberian pine (cedar) altitudinal zonal complex (AZC) to the subtaiga forest-steppe pine AZCC of forest types was revealed. Forest fires were found to cause great quantitative and qualitative changes in the chemical composition of surface organic pyrogenic horizons; they are especially manifested in the transformation of their labile properties (рН, exchangeable cations, total and mobile nitrogen, etc.).

The molecular structure of humus substances from permafrost-affected peat mounds of the East European forest-tundra has been studied with the use of up to date physicochemical methods (¹³С NMR, EPR spectroscopy). The structural-functional parameters of humus substances from these soils are specified by the integral action of cryogenic processes in the active layer, natural selection of aromatic structures in the course of humification, and by the species composition and degree of peat decomposition; they reflect the climatic conditions of peat formation in the Holocene. Humic acids of peat bogs are represented by low-condensed molecular structures with the low portion of carbon atoms of aromatic components, which increases down the soil profile, and by with the high content of non-oxidized aliphatic fragments. Active changes in the portions of aromatic and non-oxidized aliphatic fragments take place at the lower boundary of the active layer in the soils of bare peat spots. Such changes may serve as the basis for further search of the bioindicators of recent climate changes.

The formation of compacted subsoil layer under the impact heavy machines is a global problem in soil science, soil physics, and agrotechnology because of the numerous and significant effects on the water, air, and thermal regimes of soils, their permeability for root systems of plants, etc. For recent calcareous alluvial soils (Calcic Fluvisols) in the foothill areas of eastern Turkey, this problem is particularly important, because these soils were formed as a result of floods of the Aras River. These soils represent unconsolidated homogeneous formations and have a compacted horizon at the depth of 30 to 65 cm, which was formed during dozens of years. Its density almost reaches critical values for loamy soils (>1.5 g/cm³), and its penetration resistance is also high: close to 5 MPa. The studied soils are heavy loamy throughout the profile with a predominance of silt fractions (1–3 and 4–6 µm), have a low content of soil organic matter (up to 0.5% in the plow layer). In the layers of 0–30 cm and 70–150 cm, soil density and penetration resistance are not high: 1.3 g/cm³ and 2 MPa, respectively. Such a fast and deeply penetrating soil compaction is associated with the initial loose state of the soils, their heavy texture, and low content of soil organic matter—the main protector from the subsoil compaction. To prevent further development of subsoil compaction, it is recommended to optimize agrogenic loads, stop using heavy machines under conditions of the high soil water content, and to apply organic fertilizers.

Using the earlier developed MULCH model of heat-and-water exchange in the “soil–mulch cover–vegetation cover–land-surface atmosphere layer” system, we showed that the zero (minimum) tillage technology in combination with mulching the soil surface with plant residues is the most promising method for increasing the water availability and yield of wheat in steppe regions of the Crimea. It was found that the optimal thickness of the mulching layer on rainfed fields under wheat is ~4–5 cm. It was shown that minimum tillage in combination with mulching the soil surface with a 5-cm-thick layer of plant residues increases the water availability of wheat plants (which is determined by the ratio between the actual and potential transpiration of plants) on rainfed fields in the steppe regions of Crimea by 13% on the average. The yield of wheat increases compared to the conventional tillage practice (with consideration for the increase of humus content in the soil under long-term (about 8–10 years) mulching of soil surface) by 12% (~5.3 dt/ha) on the average. The obtained results can be used in the development of methods for using natural water resources in agroecosystems of the steppe Crimea.

The taxonomic composition, abundance, and diversity of bacterial and fungal communities in the rhizosphere loci and bulk mass of the gray forest soil (Eutric Retisol (Loamic, Aric, Cutanic, Humic)) under potatoes, maize, and white mustard grown with the application of mineral and organic fertilizers were compared. Among bacteria, Bacillus megaterium and Paenibacillus polymyxa species predominated in all the experimental variants. The micromycete community was represented by 39 species belonging to 19 genera. Under the impact of organic fertilizers, the abundance of Trichoderma harzianum—an antagonist of many phytopathogens—increased. A decrease in the abundance of representatives of Fusarium genus was observed both in the rhizosphere and in the bulk soil. Fertilization was the most significant factor determining the structure and diversity of micromycete communities both in the soil and rhizosphere. The application of mineral fertilizers reduced the diversity of micromycetes in soil, whereas the use of organic fertilizers increased it. In general, organic fertilizers proved to be more favorable for the rhizosphere and bulk soil mycobiomes and for the total soil suppressiveness than the mineral fertilizers.

On the Cis-Salair Plain with well-drained soils, the statistical dependence of the yield of spring wheat and NDVI on some properties of the plow horizon in eluviated clay-illuvial agrochernozems (Luvic Greyzemic Chernozems) and agro-dark gray soils (Luvic Retic Greyzemic Phaeozems) was studied. In the regression model, the NDVI was shown to be responsible for 85% of the variation in the yield of spring wheat. Using the model and the spatial distribution of NDVI as the cartographic base, the prediction and visualization of the spatial variability of the spring wheat yield was performed. The spring wheat productivity and the NDVI proved to be insignificantly different for the agro-dark gray soils and agrochernozems. The correlation was significant between the yield of spring wheat and the NDVI, on one hand, and the pre-sowing water content (r = 0.52; r = 0.57) and the content of exchangeable potassium (r_s = 0.58; r_s = 0.61), on the other hand; the correlation with the contents of humus (r = 0.35; r = 0.38), available phosphorus (r_s = 0.32; r_s = 0.35), and mobile zinc (r_s = 0.42; r_s = 0.48) was moderate. Relatively high contents of mobile forms of macro- and microelements in soils correlated with higher values of the presowing water content.