Mobile forms of phosphorus and iron compounds in chernozem-like soils in the northern part of the Tambov plain

Moisture content and redox conditions are factors determining the dynamics of the content of mobile phosphorus in chernozem-like soils moistened and waterlogged by groundwater and surface water. When the moisture content increases and oxidizing conditions are still present in soils belonging to the chernozem type that contain a high concentration of calcium phosphates, the latter transform from apatite into more mobile forms, Ca-PI and Ca-PII. In chernozem-like soils with a high concentration of iron phosphates under reducing conditions, the amount of phosphorus extracted with 0.1 N H₂SO₄ increases owing to the transition of iron phosphates into a mobile state. Precipitations enriching the soil with atmospheric oxygen promote the increase in the value of the oxidation-reduction potential (Eh), thereby decreasing the mobility of iron phosphates.     

Concretions in typical chernozem,gleyed chernozem-like,and solonetzic chernozem-like soils of the southern Tambov Lowland

A system for the diagnostics of chernozemic soils of the Tambov Lowland based on concretions is proposed for agricultural and reclamation purposes. The relationships between the structure and composition of the carbonate concretions, the long-term water regime of the soils, and the productivity of the crops have been established. The dense concretions in the typical chernozem testify to the depth of the seasonal wetting; the angular-rounded concretions in the deeply gleyed chernozem-like soil, to the upper boundary of the capillary fringe; and the angular concretions with sharp edges and cavities in the gleyic chernozem-like soils, to the groundwater table. In the chernozem-like soils that were waterlogged with bicarbonate-sodium water, the black angular concretions were formed in the solonetzic horizons, while the weakly compacted light-colored ones, in the zone of the capillary fringe. Humic acids were responsible for the color of the dark neoformations, and fulvic acids predominated in the light-colored ones. The appearance of black fine nodules indicated periodic surface water stagnation. Manganese predominantly accumulates in these nodules. The structure of the Mn-Fe concretions in the plow horizon observed at a magnification of 40–50 times has a diagnostic importance. The short-term (2–3 weeks) water stagnation leads to the formation of fine-stratified concretions, and the long-term (up to 1.5 months) stagnation promotes the formation of uniform porous ones. The solonetzic process induced by the bicarbonate-sodium water results in the appearance of mottled concretions.     

The genesis,classification, and melioration of gleyed podzolic chernozem-like soils in the north of the forest-steppe zone of European Russia

Chernozem-like soils with light-colored acid eluvial horizons are widespread in the forest-steppe zone of European Russia. Their formation is related to gleying under the conditions of a stagnant-percolative water regime on leached rocks. It is closely associated with the evolution of salinized soils (Gedroits’s scheme). However, these soils have not been included in the soil classifications of the Soviet Union and Russia. Based on the principles of substantial-genetic classification, one of the authors of this article [3–5, 10] referred them to gleyed podzolic chernozem-like soils, which are considered as an individual genetic soil type. With respect to agroecological aspects, they are different from the leached chernozems in their low productivity and difficulty of tillage. This article covers the problems of genesis, classification, and melioration of gleyed podzolic chernozem-like soils in the north of the forest-steppe zone of European Russia and their possible association with dark-colored podbels.     

Ecological-hydrological and genetic features of the soils of the Tambov Plain

Specific features of the genesis of chernozem-like, solonetzic chernozem-like soils, and hydromorphic chernozem-like solonetzes were investigated on the southern Tambov Plain. Typical chernozems occupy well drained areas. The yield of cereals is limited by the amount of precipitation. On the flat surface of weakly drained watersheds, deeply gleyed chernozem-like soils are formed under the influence of bicarbonate-calcium ground water and water stagnation on the plow sole. In closed depressions with the 1.5- to 2.0-month long stagnation of surface water on the compact lower horizons, podzolized gleyic chernozem-like soils are formed. They have favorable physical properties, weak eluvial differentiation, and rather high acidity. In humid and moderately humid years, the cereals on these soils are waterlogged; in dry years, their yield increases by 20% as compared to that on the typical chernozem. In the low undrained areas of the watersheds, solonetzic chernozem-like soils and hydromorphic chernozem-like solonetzes are formed under the influence of bicarbonate-sodium water. Despite the unfavorable physical properties of the solonetzic horizons, their better supply with moisture determines the possibility to obtain stable high yields of cereals on the solonetzic chernozem-like soils. The productivity of the gleyic chernozem-like solonetzes is low irrespective of the humidity of the year.     

Light Gray Surface-Gleyed Loamy Sandy Soils of the Northern Part of Tambov Plain: Agroecology,Properties, and Diagnostics

Light gray soils of Tambov oblast mainly develop from sandy and loamy sandy parent materials; these are the least studied soils in this region. Despite their coarse texture, these soils are subjected to surface waterlogging. They are stronger affected by the agrogenic degradation in comparison with chernozems and dark gray soils. Morphology, major elements of water regime, physical properties, and productivity of loamy sandy light gray soils with different degrees of gleyzation have been studied in the northern part of Tambov Plain in order to substantiate the appropriate methods of their management. The texture of these soils changes at the depth of 70–100 cm. The upper part is enriched in silt particles (16–30%); in the lower part, the sand content reaches 80–85%. In the nongleyed variants, middle-profile horizons contain thin iron-cemented lamellae (pseudofibers); in surface-gleyed variants, iron nodules are present in the humus horizon. The removal of clay from the humus horizon and its accumulation at the lithological contact and in pseudofibers promote surface subsidence and formation of microlows in the years with moderate and intense winter precipitation. The low range of active moisture favors desiccation of the upper horizons to the wilting point in dry years. The yield of cereal crops reaches 3.5–4.5 t/ha in the years with high and moderate summer precipitation on nongleyed and slightly gleyed light gray soils and decreases by 20–50% on strongly gleyed light gray soils. On light gray soils without irrigation, crop yields are unstable, and productivity of pastures is low. High yields of cereals and vegetables can be obtained on irrigated soils. In this case, local drainage measures should be applied to microlows; liming can be recommended to improve soil productivity.     

Neoformations (Nodules and Placic Layers) in Surface-Gleyed Loamy Sandy Soils of the Northern Part of the Tambov Plain

Eurasian Soil Science - In the middle part of the profiles of light gray soils (non-gleyed, deeply gleyed, weakly and strongly gleyed) on silty loamy sandy two-layered deposits of the river...     

Methods for quantitative diagnostics of degree of hydromorphism of chernozem-like soils (based on example of soils of northern Tambov Plain)

The hydrologic features of chernozem-like soils of the northern Tambov Plain reflect the crystallinity of nonsilicate iron contained in ferromagnetic concretions, as well as the qualitative humus content and other properties. The possibility of using Schwertmann’s criterion and swampiness coefficient in the Zaidel’man-Ogleznev method as diagnostic indices of degree of hydromorphism is shown. A new diagnostic index is suggested, i.e., the hydromorphism criterion (K_I–II); the relation of the optical density of the extraction of alkaline and alkaline pyrophosphate from fine-earth arable land horizon is based on its definition.     

Phosphate status of chernozem-like hydromorphic soils in the northern Tambov Plain

The phosphate status of chernozem-like soils in the northern forest steppe of the Tambov Lowland depends on soil waterlogging and hydrological conditions. Due to surface waterlogging and free effluent seep-age in podzolized, chernozem-like soils of open watershed depressions, the removal of bases and iron decrease the total phosphorus content by 10–15% because of the decrease in active mineral phosphates. Organic matter acts as a buffer preventing phosphorus from leaching. In podzolized, chernozem-like and podzolic, gleyic soils of closed watershed depressions, significant amounts of iron phosphates are accumulated in fine earth and ortsteins due to surface waterlogging and difficult effluent seepage. Under ground waterlogging, calcium phosphates prevail in the composition of active mineral phosphorus in the gleyed, gleyic, and gley chernozem-like soils of above-floodplain terraces.     

Chemical properties of soils in closed depressions of the northern Tambov Plain

Chemical properties of chernozem-like soils in closed depressions on different relief elements in the northern part of the Tambov Plain differ significantly. The soils with podzolic features in depressions on the watershed have a high acidity and a low degree of base saturation. The soils on the above-floodplain terrace are neutral and saturated with bases. When the degree of moistening increases, the share of magnesium in the total exchangeable bases increases to 30–35%. In the soils of surface flooding under gleyzation conditions, iron is leached from the fine earth, and iron nodules are formed. In the soils formed under the impact of groundwater, iron diffusion is observed in the surface layers. In the podzolic horizons of soils on the watershed, humus acquires a fulvic-humic character. In the soils formed under the impact of groundwater and water stagnation conditions typical for gleyed soils, the Cha: Cfa ratio is higher than 1.     

Ecological-hydrological and genetic features of chernozem-like soils of closed depressions in the northern Tambov Lowland

Specific features of the genesis and water regime of soils in closed depressions were studied in two catenas located on the interfluvial and terrace surfaces. In humid years and in the years with moderate precipitation, the surface flooding up to early May reduced the Eh values up to 60–100 mV in the soils of the interfluvial depressions. The contrasting stagnant-percolate water regime under the surface waterlogging caused podzolization of the soils manifested in the skeletans, iron nodules, humus cutans, and podzolic horizons. The pro-files acquired eluvial-illuvial differentiation, and the water-physical properties of the soils became less favorable. In the soils of the terrace depressions upon bogging due to the shallow ground water and stagnation of water up to mid-July, the Eh values decreased to ?20 to ?80 mV. The reductive conditions were responsible for the appearance of the morphochromatic signs of gley. The ground water of bicarbonate-calcium composition at a depth of 80–120 cm hindered podzolization. The soils with features of gley and podzolization are low-productive.