Biological activity in the profiles of chernozems as dependent on the character of their agricultural use and microtopography

The biological activity of soil samples taken from genetic horizons of plowed and virgin chernozems in the Kamennaya Steppe Reserve was determined as the amount evolved from the soil upon its incubation in laboratory conditions. In the top humus horizons, the biological activity of virgin chernozem was two to three times higher as compared with that in the plowed chernozem. The intensity of biological processes and the microbial biomass in the soil profile was mainly controlled by the quantity and quality of soil organic matter. Long-term agricultural use exerted a weaker effect on the biological properties of chernozems developed on microelevations (blocks) of the paleocryogenic microtopography in comparison with chernozems developed in the microdepressions between the blocks. The factor analysis showed that soil characteristics related to the biological processes comprise more than 50% of the total variance of factor loads and are distinctly differentiated in the soil profile.     

Mineralization of organic matter and the carbon sequestration capacity of zonal soils

The susceptibility of soil organic matter (SOM) to mineralization decreases in the following sequence of zonal soils: tundra soil > soddy-podzolic soil > gray forest soil > chestnut soil > dark chestnut soil > chernozem. The content of potentially mineralizable organic matter in the plowed soils is 1.9–3.9 times lower than that in their virgin analogues. The highest soil carbon sequestration capacity (SCSC) is typical of the leached chernozems, and the lowest SCSC is typical of the tundra soil. Taking into account the real soil temperatures and the duration of the warm season, the SCSC values decrease in the following sequence: leached chernozem > dark chestnut soil > chestnut soil ≥ tundra soil > gray forest soil > soddy-podzolic soil. Arable soils are characterized by higher SCSC values in comparison with their virgin analogues.     

Effect of paleocryogenesis on the soil cover pattern and properties of chernozems in the Kamennaya Steppe Reserve

The paleocryogenic genesis of a polygonal-blocky microrelief is substantiated. This microrelief was formed at the end of Late Pleistocene and is preserved in the buried state; it is also pronounced in the surface microtopography. The modern development of chernozems is greatly influenced by the paleocryogenic microtopography, as the profiles of chernozems developed on elevated polygons, their slopes, and within interpolygonal microdepressions clearly differ from one another in their morphology, horizonation, and functioning. These differences are sufficient to subdivide the corresponding soils at the subtype level. The paleoenvironmental reconstruction of the early (paleocryogenic) stages of the development of chernozems and the study of modern soil functioning with due account for the effect of paleocryogenic phenomena have been performed for the first time.     

Soil polygenesis in the northeast part of Vladimir opolie

Soil studies in cultural landscapes of the medieval epoch within the Vladimir opolie territory on the Russian Plain suggest that virtually all automorphic soils in this area were plowed in that period. The morphology of the profiles of studied soils depends on the composition of parent materials. If the parent material represents a pedocyclith that passed through the stage of periglacial pedogenesis in the Late Pleistocene, then the soil profile developed from this material is a heterochronous body with distinct features of polygenesis. If the parent material is a relatively homogeneous sediment that was not subjected to periglacial pedogenesis in the Late Pleistocene, then the soil profile developed from this material contains only the features of the Holocene pedogenesis, even in the case when the thickness of the homogeneous substrate does not exceed 0.5 m. It is hypothesized that the Holocene pedogenesis within the humid forest and southern taiga zones in the center of the Russian Plain cannot delete the features of the pre-Holocene pedogenesis and morpholithogenesis; these features are always inherited by the profiles of modern soils. The presence of these features ensures the development of a fully developed mature soil profile.     

Experimental determination of the active organic matter content in some soils of natural and agricultural ecosystems

In incubation experiments, the soil supply with carbon of mineralizable (C_min), potentially mineralizable (C_pm), and active (C_ac) organic matter, and of microbial mass (C_mb) in natural and agricultural ecosystems of Moscow region (gray forest soil) and Catalonia (Xerochrept) was assessed based on the measurements of the C-CO₂ emission. In the gray forest soil, the C_pm and C_ac contents decreased in the following sequence of ecosystems: forest > meadow > unfertilized agrocenosis; in the Xerochrept, forest > pasture > scrub > agrocenoses with organic fertilizer > unfertilized agrocenosis. A method for measurement of the C_mb according to the C-CO₂ emission during an 11-to 14-day incubation of previously dried soils is proposed.     

Humification and nonhumification pathways of the organic matter stabilization in soil: A review

Polymeric and supramolecular models of humic substances (HSs) are considered. It has been noted that the HSs in natural objects can simultaneously occur in the forms of macromolecular polymers and supramolecularly organized monomers; macromolecular polymers of HSs can have some properties of suprastructures or be associated into aggregates, and covalent bonds can be formed between the monomers of supramolecules. Mineral particles of soil act as catalysts in chemical reactions between individual compounds, sorbents of biomolecules, and a surface for self-assembling HSs. It is supposed that the combination of such physicochemical processes and phenomena in soil as cementation, charring, incrustation, occlusion, sedimentation, sorption, coagulation, flocculation, encapsulation, complexation, and intercalation, as well as the entrapment of macroorganic, particulate, and soluble organic substances in micropores, can be as important for the stabilization of organic matter as the interactions between biomolecules with the formation of HSs.     

Organic matter mineralization in different soil aggregate fractions

The mineralization rate of the organic matter (OM) in the aggregate fractions of a gray forest soil separated by repeated sieving through sieves with different mesh sizes was assessed. The samples of the soil aggregate fractions were incubated for 141 days under constant temperature and moisture, and the C-CO₂ emission rate was measured. The mineralizable OM pool in the aggregates of <0.25, 1–0.25, and 3–1 mm in size from the soil under a forest contained easily (C₁, k ₁ > 0.1 days⁻¹), moderately (C₂, k ₂ > 0.01 days⁻¹), and difficultly (C₃, k ₃ > 0.001 days⁻¹) mineralized compounds; the C₁ and C₂ components were present in the coarser aggregates. In the arable soil, the C₁, C₂, and C₃ OM components were separated in the aggregates of <0.25 and 1–0.25 mm; the C₁ and C₃ were separated in the aggregates of 3–1 and 5–3 mm; and the C₁ and C₂ were separated in the coarsest (10–5 mm) aggregates. The highest content of potentially mineralized OM (C₀) occurred in the aggregates of 1–0.25 and 3–1 mm, but the size of the mineralizable OM pool was more dependent on the portion of the aggregate fraction in the soil than on the absolute C₀ content in the fraction. It was shown that the decrease in the share of coarse structural aggregates is accompanied by a depletion of potentially mineralized OM in the arable soil, and the formation of coarse aggregates is an important condition of the soil carbon sequestration.     

Biokinetic indication of the mineralizable pool of soil organic matter

In three laboratory experiments with gray forest soils, the rates of mineralization of the bacterial mass, green oat mass, and cellulose applied in increasing doses were determined based on the measurement of the C-CO₂ emission. The substances applied were used as biological indicators of the mineralizable organic matter pool in the gray forest soils.     

Hydrothermic conditions of functioning of gray soils: Assessment and prognosis

The revealed trends of temperature and precipitation changes between 1932 and 2001 suggest that the nearest ten years in the southern Moscow region should be characterized by the fall in soil temperatures and the rise in the soil water content during the growing season in spite of the significant shift in the water and temperature regimes of plowed soils toward the aridity and higher continentality of their climate. The resulting situation can affect agricultural production by favoring the transition from high-input farming to grass farming in the southern Moscow region.