No 7 (2024)

We studied the composition of water-extractable organic matter (WEOM) of reclaimed soils (Novic Protocalcic Chernozems) in the unplowed bottom of the dry valley and to compared it with the composition of WEOM of the plowed soils (Protocalcic Chernozems) on cropland in the small catchment. A layer-by-layer study of the composition of the WEOM of reclaimed soils was carried out from the surface to a depth of 120 cm with a step of 20 cm. Aqueous extracts were characterized by the content of organic carbon, nitrogen and pH value. The optical properties of WEOM were assessed by spectrophotometry and fluorescence spectroscopy. The optical properties of WEOM of Protocalcic Chernozems were compared with those of sediments. The features of changes in these properties with depth in sediments were also analyzed. It was revealed that erosion-accumulation processes have a significant impact on the composition of soil WEOM. The content of dissolved carbon in WEOM does not differ significantly either between arable chernozems and sediments, or along the depth of the vertical profiles of sediments. At the same time, content of nitrogen WEOM in the arable chernozems is generally higher than in the sediments, and in the sediments it naturally decreases with the depth. Probably the decrease of nitrogen content of WEOM with the depth of sediments is associated with its absorption by plant roots and with an increase with the depth in the proportion of anaerobic zones where denitrification processes are activated. The top 0–60 cm of soil sediments actively retain nutrients leached from arable soils, primarily dissolved nitrogen. This process promotes the accumulation of carbon in the underlying layers. The increase in the content of total organic carbon in Novic Protocalcic Chernozems layers deeper than 60 cm can be explained by the accumulation of DOM penetrating from above. DOM in the lower layers of Novic Protocalcic Chernozems, on the one hand, is sorbed by the soil, and on the other hand, it is preserved due to a decrease in microbial activity due to a lack of nutrients.

Analysis of the stable carbon isotopic composition (δ¹³C) of soil organic matter plays an important role in assessing past climate changes and feedback of landscape components. The object of the study was the soils of nine soil-sedimentary sequences formed in various landscape and geomorphological conditions of the Western Transbaikal region. The formation time of sections covers the last 15 kyr. The phases of pedogenesis occurred quite synchronously within genetically different landforms, which allows us to consider them as caused by regional landscape-climatic changes, which also influenced the δ¹³C of soil organic matter. There is a wide range of variations in δ¹³С values (from –20.99 to –27.00‰). The most contrasting changes in δ¹³С values over time were noted for sections formed in the driest steppe conditions; the smallest amplitude of δ¹³С values is characteristic of sections formed under taiga landscapes with the greatest moisture. However, in general, the trends in changes in δ¹³С values over time within different landscape zones are similar: the lowest δ¹³С values are characteristic of the organic matter of Late Glacial soils formed 14–15 and 12 kyr BP, as well as soils of the late Holocene (3.5–2.0 and 1.0–0.3 kyr BP). The organic matter of soils of the Middle Holocene (9.0–4.0 kyr BP) and the time interval of 13–14 kyr BP is enriched in ¹³C. Based on the identified dependence of the δ¹³C values of organic matter of modern soils in the region on the amount of precipitation, a quantitative reconstruction of precipitation during the growing season was carried out. The data obtained allow us to estimate the time intervals of 11.7–10.0 and 4.0–1.5 kyr BP as the most optimal for the formation of soils in Western Transbaikalia. An increase in temperatures and a decrease in atmospheric humidity in the Middle Holocene, characteristic of both Transbaikalia and adjacent territories, had a negative impact on the intensity of pedogenesis.

The chemical structure of pools of organic matter (OM) in the 2–1 mm water-stable macroaggregates, isolated from air-dry aggregates of the same size in arable horizons of non-eroded, eroded and deposited agrochernozems has been studied by solid-state ¹³C-NMR spectroscopy. An assessment is made of the alteration of their chemical structure in the denudative-accumulative landscape. It was revealed that the overwhelming majority of water-stable macroaggregates in the erosion zone are newly formed due to the dynamic replacement of OM in situ, which is clearly evidenced by the integral indicators of the chemical structure of all pools of OM macroaggregates. Analytical data indicate the predominant transport of newly formed macroaggregates. The destruction of macroaggregates during the transport phase is accompanied by the release of previously physically protected aggregated OM, which undergoes partial mineralization (predominantly its most labile part – hydrolyzable), and its stable part remains little/non-changed. Mineral-associated OM (Сlay and Residue) changes little, maintaining relative freshness, which may be indirect evidence of the transportation of predominantly newly formed macroaggregates from the erosion zone. The greater degree of freshness of free OM of macroaggregates in deposited agrochernozem is due to the predominance in of fresh remains of cultivated vegetation of the accumulative zone, together with those transported from the erosion zone.

Based on a significant volume of soil samples of various genesis presented on the territory of the Komi Republic, a study of their granulometric composition (GC) was carried out in accordance with the Kachinsky method (MK). Calculated, procedural, random and systematic factors influencing the precision and correctness of measurement results performed in accordance with the MK prescription are considered. The influence of sample preparation (the degree of grinding of soil samples) and procedures for measuring the mass fraction of elementary soil particles (ESP) on the quality of the results of studying soil GS was assessed. The instability of measuring the mass fraction of fine sand (0.05–0.25 mm) and coarse dust (0.01–0.05 mm) fractions when using the MK recipe was shown. The dependence of the uncertainty of measurement results, caused by random factors, on the mass fraction of ECPs included in the granulometric fractions is noted – the lower the mass fraction of ECPs in the composition of the fractions, the higher the uncertainty of the measurement results. A modification of the Kaczynski method (MMK) has been developed to improve the quality of soil HS assessment results. It includes: (1) separation of fine sand particles using a sieve with a mesh diameter of 0.05 mm (instead of calculating this fraction by difference according to the MK recipe); (2) use of scales of the first class of accuracy to measure the mass fraction of dust and sludge particles; (3) control of the HS research process based on the summation of the measured values of the mass fraction of ESP of six fractions and acid-soluble compounds (losses from HCl treatment). The standard for operational control of the mass fraction of the amount of ECP after dividing them into fractions is (100 ± 5)%. A metrological study of the Kaczynski technique and its modifications was carried out. The proposed modification of Kaczynski’s technique made it possible to reduce the uncertainty in the measurement results of the mass fraction of ECP of small fractions (ω_n < 10%) and shift the lower limit of measurements to 1%.

The carbon content of microbial biomass in the soil serves as one of the indicators of its biological activity and is often used in assessing the anthropogenic impact and natural changes on the soil microbiome. Significant spatial and temporal variation of the indicator at the level of ecosystems, soil typological units, land use types, etc. makes it difficult to interpret the data obtained during mass monitoring. The aim of the study is to determine the background values of microbial biomass content in the surface sub-litter layer of soils of protected forests of the Moscow region. A reconnaissance survey of soils of the podzolic series, which are typical for the region and diverse in genesis and granulometric composition, autonomous or with a little additional moisture, formed under mixed southern taiga forests in four protected natural territories, was carried out. The biological activity of soils was estimated by the amount of microbial biomass determined by two methods: by the content of phospholipids and substrate-induced respiration of microbial communities. Significant spatial variability of microbial biomass content was noted both at the site level and at the ecosystem level, and for similar by classification and granulometric composition autonomous soils, it is comparable with local variability within the experimental sites. It is shown that the value of microbial biomass depends mainly on the type of the humidity regime and the granulometric composition, which largely determines the sorption capacity of the soil, and its provision with biophilic elements, and also correlates with the richness of the ground cover that provides the soil microbiome with nutrients. It is shown that in order to obtain correct results for mass monitoring of soil biological activity, unification of the methodology and depth of sampling in the soils of background and anthropogenic-transformed ecosystems is of great importance.

The experimental assessment of soil erodibility using the methodology of washing out model samples with a water stream at different installations (hydraulic flume, jet unit, and water tunnel) that were carried out earlier, usually produced a high variability of results. The intension to decrease this variability resulted in a development of a new horizontal approach to samples formation, which differed from the previous one by loading the sample through a removable side wall of the horizontally placed cartridge. The layered loading and compaction remained the same. The normal positioning of sample layers against the flow compared to the parallel positioning practiced earlier allowed to reach a more uniform sample resistance to the flow. The use of the “Poseidon” measuring unit developed to define mean depth of the wave flow, allowed to not only to increase many-fold the number of measurements of washout intensity during the experiment (from 1 to 14–15), but also to assess the quality of sample preparation, which increased precision and accuracy of the study. It has been determined that the percentage standard deviation for erodibility was almost always lower with the horizontal loading compared to the vertical one both between and within the series (13 and 12% on average respectively).