Vol 49, No 1 (2016)

Quasi-gley chernozems of the Trans-Baikal region are characterized by the clearly pronounced anisotropy of their properties related to carbon sequestration processes. The main carbon pool is concentrated in the humus horizon; the organic carbon content sharply decreases down the soil profile. The pool of organic carbon in the cryogenic fissures is two to three times higher than its pool in the enclosing soil horizons. The analysis of stable carbon isotopes in the plants and soils attests to the predominance of C3 plants. The composition of stable carbon isotopes is clearly differentiated in the soil profile with an increase in the portion of heavy isotopes in the deep horizons. In the humus pockets and cryogenic fissures, the increase in the portion of heavy carbon isotopes with the depth is weaker, which attests to a lower degree of the organic matter transformation. It is probable that the organic matter in the fissures is younger than the organic matter in the enclosing soil mass and derives from the upper humus horizon. The organic matter in the cryogenic fissures preserves the evolutionary properties of humus from the upper horizons.

A new notion—an acidic trace of pedogenesis in the field of soil acidity—is suggested. This notion implies a three-dimensional representation of the distribution of soil acidity in the soil profile and can be graphically shown in three two-dimensional projections that can be combined on a common V-diagram. Such V-diagrams are individual for each particular soil profile. At the same time, they have some common phenomenology in their shapes and in the position in the acidity field. A tendency for the S-shaped form of acidic trace is manifested by a sharp decrease in pH upon the reduction of base saturation at the high and low values of this index and by small changes in pH at the moderate values of base saturation in the area of acid buffering of the soil profile. This phenomenon is related to the weak acidity and polyfunctionality of the soils as ionite systems. An acidic trace can be subdivided into several characteristic parts related to different pedogenetic processes in their interaction. Its position in the field of acidity is largely determined by the acidity of parent material. Acidic traces of different types of soils in the northwestern Russia are discussed. It is argued that V-diagrams should be analyzed together with other soil characteristics.

The impact of slope aspect and gradient on the contents and distribution of heavy metals (Mn, Cu, Zn, Co, Ni, Pb, and Cd) in the profiles of ordinary chernozem (Haplic Chernozems) was studied in Kursk oblast. Slope aspect was found to be a significant factor controlling the distribution of most of the bulk, mobile, and acid-soluble compounds of heavy metals, whereas the position on the slope (slope gradient) did not exert a significant influence on the distribution of elements. Bulk compounds of Co, Ni, Pb, and Cd showed the eluvial type of distribution in the soil profiles along with accumulation in the lower horizons. Distribution patterns of the mobile Cu, Co, Ni, Pb, and Cd were similar to those of the bulk ones. The latter phenomenon may be attributed to the high content of carbonates, an increased content of clay, and some alkalization of the soil solution in the lower horizons.

Microbial communities of recent surface soils and the soils buried beneath the rampart of the Tsaritsyn Defense Line (1718–1720) in the Little Ice Age were studied. The contribution of the time factor to the variability in the number of microorganisms from different trophic groups was shown to be minor (0.2–0.3%), although significant. In the upper horizon of the paleosols reflecting the environmental conditions intrinsic to the period of the rampart construction, the lower (by two times) content of live microbial biomass, the lower metabolic activity of the microbial community, and the more contrasting changes in the microbiological parameters as compared to these characteristics in the recent soils were found for all the elements of the local topography. The stabilities of the microbial communities in the buried and recent soils were almost the same. The ecological–trophic structure of the microbial communities in the buried soils evidences that, the climate of the 18th century in the southern Privolzhskaya Upland was more humid than now. At the same time, temperature conditions of the Little Ice Age did not prevent the development of steppe vegetation and corresponding soil microbial communities in this area. Our data on the morphology and physicochemical properties of the soils confirm the assumption about more humid climatic conditions at the beginning of the 18th century in the studied area.

The analysis of publications on soil food webs (FWs) allowed calculation of the contents of soil fauna metabolites and dead mass, which can serve as materials for humification. Excreta production of FWmicrofauna reaches 570 kg/ha annually, but the liquid excreta of protozoa and nematodes compose about 25%. The soil fauna dead mass can be also maximally about 580 kg/ha per year. However, up to 70% of this material is a dead mass of bacteria, protozoa, and nematodes. The undecomposed forest floor (L) has low values of these metabolites in comparison with the raw humus organic layer (F + H). The mass of these metabolites is twice lower in Ah. Theoretical assessment of earthworms’ role in SOM formation shows that the SOM amount in fresh coprolites can be 1.4 to 4.5-fold higher than SOM in the bulk soil in dependence on food assimilation efficiency, the soil: litter ratio in the earthworms’ ration, and SOM quantity in the bulk soil. Excreta production varies from 0.2 to 1.9% of the total SOM pool annually, including 0.15–1.5% of excrements of arthropods and enchytraeidae, but the amount of arthropods’ dead mass comprises 0.2–0.4%. The calculated values of the SOM increase due to earthworms’ coprolites are of the same order (0.9–2.7% of SOM pool annually). These values of SOM-forming biota metabolites and dead mass are close to the experimental and simulated data on labile and stable SOM fractions decomposition in forest soils (about 2% annually). Therefore, these biota’s products can play a role to restock SOM decrease due to mineralization.

The effect of land use types and fertilizing systems on the structural and aggregate composition of loamy sandy soddy-podzolic soil and the quantitative parameters of soil organic matter has been studied. The contribution of soil aggregates 2–1 mm in size to the total C_org reserve in the humus horizon is higher than the contributions of other aggregates by 1.3–4.2 times. Reliable correlations have been revealed between the contents of total (C_org), labile (C_lab), and active (C₀) organic matter in the soil. The proportion of C₀ is 44–70% of C_lab extractable by neutral sodium pyrophosphate solution. The contributions of each of the 2–1, 0.5–0.25, and <0.25 mm fractions to the total C₀ reserve are 14–21%; the contributions of each of the other fractions are 4–12%. The chemically labile and biologically active components of humic substances reflect the quality changes of soil organic matter under agrogenic impacts. A conceptual scheme has been proposed for the subdivision of soil organic matter into the active, slow (intermediate), and passive pools. In the humus horizon of loamy sandy soddy-podzolic soil, the active, slow, and passive pools contain 6–11, 34–65, and 26–94% of the total C_org, respectively.

Changes in the fertility of a leached chernozem under different tillage technologies (moldboard, non-inversive, and combined tillage) were studied in a multifactor stationary field experiment established in 1985 in Voronezh oblast on a low-humus medium-deep light clayey leached chernozem. The nine-field rotation of cereals and sugar beet was practiced. It was found that the major parameters of soil fertility—the content and qualitative composition of humus and the physicochemical and physical properties of the chernozem—remained relatively stable independently from the applied primary tillage technologies. However, taking into account economic characteristics (crop yields, production costs, energy expenses, etc.), the combined tillage system proved to be most efficient. It can be recommended for cereals–sugar beet rotation systems in the central chernozemic region, as it ensures the highest efficiency of crop growing and preserves the fertility of leached chernozems.

The properties of loamy sandy postagrogenic soils in the course of their natural overgrowing were studied in the southeastern part of Kostroma oblast. Micromorphological indications of tillage were preserved in these soils at least 35–40 years after the cessation of their agricultural use. In the course of the soil overgrowing with forest vegetation, the bulk density of the upper part of the former plow horizon decreased, the pH and the ash content of the litter horizon somewhat lowered with a simultaneous increase in the acidity of the upper mineral horizon, especially at the beginning of the formation of the tree stand. In 5–7 years after the cessation of tillage, the former plow horizon was differentiated with respect to the organic carbon content. The total pool of organic carbon in the upper 30 cm increased. In the course of the further development, in the postagrogenic soil under the 90to 100-year-old forest, the organic carbon pool in this layer became lower. The soil of the young fallow (5–7 years) was characterized by the higher values of the microbial biomass in the upper mineral horizon in comparison with that in the plowed soil. In general, the microbial biomass in the studied postagrogenic ecosystems (the soils of the fields abandoned in 2005 and 2000 and the soil under the secondary 40-year-old forest) was lower than that in the soil of the subclimax 90to 100-year-old forest. The enzymatic activity of the soils tends to increase during the succession. The restoration of the invertase and, partly, catalase activities to the values typical of the soils under mature forests takes place in about 40 years.