Počvovedenie

The article considers the chemical properties and biological activity of soils of agricultural terraces on clay shales in the mid-mountain zone of the Eastern Caucasus. It is established that the area of terraced plots in the southern zone of Shale Dagestan is about 264 km² of the territory. These soils are currently in a fallow state but represent a significant reserve of highly fertile erosion-resistant soils, the cultivation of which, unlike soils on consolidated rocks, is possible with the help of modern technology. The influence of slope exposure, steepness, terrace size, duration of the plowing period on the chemical properties and biological activity of soils has been studied. It is shown that for background soils outside the terracing zone, the slope exposure has a decisive influence. For terraced areas, the impact of exposure is less pronounced. The formation of a vertical terraced surface led to a change in the thermal regime, as a result of which the differences in chemical and microbiological properties of soils on the slopes of the northern and southern exposures became less pronounced. The leveling effect of terracing is most noticeable on relatively gentle slopes (12°–18°), where the width of the terraced canvas is greatest. On steep slopes (>20°) with narrow terraces, the influence of slope exposure on soil properties remains. At the same time, factors such as the duration of soil functioning and the features of agricultural technology have no less significant impact on soil properties. The regularities of changes in soil properties within the body of any single terrace have been established. The most fertile area within one terrace is the instrument part, where the profile depth is greatest. As we approach the rear seam of the terrace, a natural decrease in a number of biological and chemical indicators is observed.

The chemical structure of organic matter (OM) pools in agrochernozems confined to different zones of denudation-accumulation has been studied by solid-state ¹³C-NMR spectroscopy. It was revealed that in the erosion zone there are two competing processes occurring simultaneously: the decomposition of the “old” OM of the earlier underlying horizon and the stabilization of the fresh OM that has arrived with plant remains of cultivated plants (dynamic replacement of OM). Analytical data allow us to assert that the processes of dynamic replacement of eroded OM in the erosive zone quite effectively compensate for the processes of OM decomposition, as evidenced by the highest C/N ratio of all the studied OM pools in the eroding agrochernozem, along with the absence of significant differences in the integral indicators of their chemical structure. However, the constant removal of the upper soil layer from the eroding agrochernozem during each erosion event does not allow one to fully compensate for the OM quantitative losses in it. During the transportation of eroded material to the accumulative zone, the most labile part of OM can be mineralized. Accordingly, the OM again entering the accumulative zone is more transformed than that of the eroding agrochernozem. Nevertheless, the alluvial agrochernozem is characterized by an increased level of C accumulation in the soil as a whole and in all the studied OM pools. Accordingly, it can be stated that the constant OM inputs from the eroding position with its subsequent burial with each subsequent erosion event, as well as the repacking/aggregation of newly deposited OM, very effectively contribute to the deposition of C in the accumulative zone.

The regular application of mineral and organic fertilizers is one of the essential components of the agricultural intensification. The applied fertilizers lead to artificial enrichment of the soil environment with readily available substrates and biophilic elements, which can have a significant impact on the soil and rhizosphere microbiome. The aim of the study was to investigate the effect of different fertilizer systems on the quantitative parameters of various microbial groups in soddy-podzolic soil (Umbric Albic Retisol) and the rhizosphere of potatoes and barley. The study was carried out on a long-term field experiment, in which mineral (NPK), organic (manure) and mixed (NPK + manure) fertilizer systems have been applied since 1968. The application of organic fertilizers increased the microbial biomass carbon (Cmic) in the bulk soil and the rhizosphere by 25–100% compared to the soil without fertilizers, while the use of mineral fertilizers, on the contrary, decreased it by 10–30%. Basal respiration and respiratory coefficient (qСО₂) increased in the row: without fertilizers < NPK < NPK + manure < manure. The gene copies number of bacteria, archaea, and fungi significantly increased (1.5–2.5 times) under organic fertilizers and decreased (2–2.5 times) under NPK. The varied from 32 to 100 and from 0.10 to 0.92 by the luminescent microscopy and quantitative PCR, respectively. The lowest fungi/bacteria ratios were revealed for variants with NPK, and the highest fungi/bacteria ratios were in variants with manure. Thus, the applied doses of mineral fertilizers must be compensated by the introduction of fresh organic matter in order to maintain the stability of the soil-microbe-plant system.

The transformation of organic matter in the soil is largely determined by hydrolytic enzymes. Under the conditions of climate change, understanding the mechanisms of microbial response is of particular importance for predicting the carbon cycle. Until now, the effect of drought duration and frequency on soil hydrolytic enzymes has been little studied. A multifactorial field manipulation experiment was carried out, simulating in the presence of plants and without them: two short-term droughts, a long-term drought, and an optimal level of soil moisture. The maximum reaction rate V_max, Michaelis constant K_m, and catalytic efficiency K_a of five groups of enzymes involved in the carbon cycle (cellobiase, glucosidase, xylanase), phosphorus (phosphatase), and nitrogen (chitinase) were determined. In phosphatases, glucosidases, and xylanases, V_max decreased during short-term drought. During prolonged drought, the V_max value of phosphatases, cellobiohydrolases, and xylanases decreased and increased in chitinases, while remaining unchanged in glucosidases. Both long-term and short-term droughts led to an increase in K_m and a decrease in catalytic efficiency (K_a) for almost all enzymes. Short-term droughts were not a “weakened version” of a long-term drought, but had their own specifics – a decrease in K_m in glucosidases, which led to an increase in K_a. Long-term drought was characterized by an increase in V_max of chitinases and spatial variability of V_max of phosphatases and glucosidases. The influence of the presence of plants was secondary and affected only during short droughts. The reversibility of the effect of drought on V_max, K_m, K_a decreased in the series first short-term drought > second short-term drought > long-term drought due to an increase in the total duration of the stress impact.

The methodological possibilities of micromorphological soil research making it possible to analyze digital images of soil thin sections at a quantitative level are presented in this study. A new software Thixomet Pro has been tested for quantitative micromorphological study of sail on the example of soil thin sections from the surface horizons of Haplic Chernozem. Soil samples for preparing thin sections were collected on the territory of scientific and industrial field test plot for assessing the impact of agro technologies in grain crop rotation on soil properties (Kursk region, Russia). In the field test plot, conventional agro technology (real tillage) and no-till are compared. Soil sampling was carried out in two replications from depth of 10–15 cm. The analysis revealed the variability of microstructure of Haplic Chernozem in the size, shape and orientation of aggregates associated with the use of agricultural technologies with and without plowing in grain crop rotation. In the Сhernozem with no–till, aggregates are generally larger compared to the aggregates of Сhernozem with conventional agro technology. This is noted at all levels of comparison of direct seeding and conventional agricultural technology: in the minimum diameter, the fraction 1–2 mm prevails against 0.25–0.5 mm, respectively, in the average diameter, fractions 1–2, 2–3 and 3–5 mm prevail against 0.5–1 and 0.25–0.5 mm, respectively, in the maximum diameter, fractions 1–2, 2–3 and 3–5 mm prevail against 0.5–1, 0.25–0.5 and 1–2 mm, respectively. It is also shown that less rounded and isometric aggregates are formed during direct seeding. With direct seeding, the proportion of aggregates with a form factor of 0.2–0.4 is higher and the proportion of aggregates with a form factor of 0.4–0.6 is lower than with traditional technology. The proportion of subhorizontal aggregates in direct seeding is higher compared to traditional processing (54.3 and 34.1% respectively).

The indicators of biological activity (humus content and reserves, microbial biomass carbon content and reserves, activity of hydrolase and oxidoreductase class enzymes) in the upper horizons (0–10 cm) of mountain meadow-steppe soils of the Central Caucasus (Kabardino-Balkaria) were determined at different stages of pasture digression (D1, D2, D3). It was found that the values of controlled soil parameters in conditions of weakly (D1) and moderately disturbed (D2) meadow phytocenoses did not significantly differ (t < 1.97; P > 0.05). Statistically significant decreases (t > 2.95; P < 0.05) in biological parameters were revealed in soils of severely disturbed meadow steppes (D3) compared with less damaged meadows (D1 and D2). Based on the totality of the studied indicators of biological activity, an integral indicator of the ecological and biological state of soils (IIEBSS) is calculated, reflecting the overall level of biological activity of the studied soils at different stages of digression of meadow-steppe communities. There was a decrease in the IIEBSS of moderately grazed (D2) and overgrazed (D3) meadows relative to the values of the conditional standard (D1) by 11and 45%, respectively. The obtained results of the biological state of mountain meadow-steppe soils are used for monitoring studies aimed at assessing the degree of change in the soil and vegetation cover of mountain pasture ecosystems.