Rhizoliths in Devonian and Early Carboniferous Paleosols and Their Paleoecological Interpretation

Eurasian Soil Science - Collected in situ rhizoliths (>20) from Devonian and Early Carboniferous paleosols in the southern part of the Russian Platform (Kaluga, Belgorod, and Voronezh...     

Soil microstructure and factors of its formation

The microstructural stability of soils of different geneses (steppe soils, tropical soils, and subtropical soils) developed from marine clay, loess, and weathering crusts was studied by the method of successive treatments with chemical reagents destroying the particular clay-aggregating components. The following dispersing agents were used: (1) H₂O (pH 5.5), (2) 0.1 N NaCl (pH 6), (3) 0.002% Na₂CO₃ (pH 8.7), (4) 0.1 N NaOH (pH 11.5), (5) the Tamm reagent (pH 3.2), and (6) 0.1 N NaOH (pH 11.5). The properties of the clay subfractions obtained in the course of these treatments were studied by a set of analytical methods, including X-ray diffractometry, Mössbauer spectroscopy, and magnetic measurements. It was shown that soil microaggregates are formed under the impact of a number of physicochemical processes; the content and properties of inorganic components (clay minerals in soils with a high CEC and iron oxides in soils with a low CEC) are the controlling factors. The structure of the parent materials is transformed to different degrees to form the soil structure. For example, autonomous nondifferentiated soils inherit, to some extent, the specific microorganization of the parent material. At the same time, the redistribution of substances in the soil profile and in the landscape may exert a substantial influence on the soil structure and microstructure. This is particularly true for autonomous differentiated soils, turbated soils, accumulative soils, polylithogenic soils, and polygenetic soils. The properties of the obtained subfractions of the clay (the mineralogical composition, the Fe²⁺/(Fe²⁺ + Fe³⁺) ratio, the magnetic susceptibility, and the Cha/Cfa ratio) attest to the spatial heterogeneity of the composition and properties of the mineral and organic aggregated compounds in soils.     

Water stability of aggregates in subtropical and tropical soils (Georgia and China) and its relationships with the mineralogy and chemical properties

Water-stable aggregates isolated from three subtropical and one tropical soil (Western Georgia and China) were studied for their organic carbon, cation exchange capacity (CEC), specific surface area, magnetic susceptibility, and total chemical elements. The soils were also studied for their particle-size distribution, mineralogy, and nonsilicate Fe and Al oxides. Describe the water stability, three indices have been used: the content of water-stable macroaggregates (>0.25 mm), the mean weighted diameter of the aggregates, and the numerical aggregation index. The yellow-cinnamonic soil (China) was neutral, and the three other soils were acid. The soils were degraded with a low content of organic matter. The yellow-cinnamonic soil was characterized by the lowest water stability due to the predominantly vermiculite composition of the clay. The high water stability of the Oxisol structure was determined by the kaolinites and high content of oxides. In three out of the four soils studied, the hierarchical levels of the soil structure organization were defined; they were identified by the content of organic matter and the Ca + Mg (in Oxisols). Iron oxides mainly participated in the formation of micro-aggregates; Al and Mn contributed to the formation of macroaggregates. The water-stable aggregates acted as sorption geochemical barriers and accumulated Pb, Zn, Cd, Cs, and other trace elements up to concentrations exceeding their levels in the soil by 5 times and more. The highest correlations were obtained with CEC, Mn, and P rather than with organic carbon and Fe.     

Modifications of the mineralogical composition and surface properties of soils as related to steppe climate dynamics in historical time

This work presents the results of a study of changes in the soil mineral components and the related modifications of the chemical composition and surface properties of soils in the desert-steppe zone in the southern part of the Ergeni Upland. Burial mounds dating back to the Bronze epoch have been investigated. According to radiocarbon data, their ages are estimated at 5100 ± 50, 4410 ± 100, 4260 ± 120, 4120 ± 70, and 3960 ± 40 years. The substantial transformation of the clay minerals, the molar chemical coefficients, the magnetic mineralogy, and the surface properties of the soils permits us to assess the rates of the mineralogical transformations caused by the climate change during the time interval of less than <∼100 years. The ratio between the content of the mineral phases in the buried soils of different ages testifies to the primary importance of climatic factor in comparison with the total duration of weathering or the soil existence on the land surface prior to its burial, i.e., the soil age.     

Some characteristics of organic soils irrigated with municipal wastewater

Soil irrigation with wastewater (WW) gives the opportunity to solve the problems of its disposal, final purification or reuse. Many studies have examined mineral soils upon continued WW application. The aim of this paper was to examine the properties of organic soils 3 years after WW application was discontinued. Peat‐muck soil planted with Populus spp. or Salix spp., and mineral‐muck soil under grasses were irrigated for 4 years with municipal WW at a low (comparable with intensive NPK fertilization) and high WW rate (600 and 1200 mm yearly, respectively). Soils were analysed for organic matter (OM), pH, bulk density (BD), water holding capacity (WHC), P₂O₅, Fe₂O₃, Al₂O₃, MnO, Zn, Pb, Cu, Cr, magnetic susceptibility (MS) and dehydrogenase and catalase activities. The results were compared with control soils which have never received WW. The study showed that only P₂O₅, MnO and catalase activity (CA) were significantly affected by former WW application. On average, P₂O₅ increased by 30 per cent, whereas MnO decreased by 35 per cent with no differences between the two WW rates. CA decreased by 18 per cent at the high WW rate. Most of tested characteristics were determined by soil type. The peat‐muck soil showed higher OM, WHC, P₂O₅, MnO, Pb and CA than mineral‐muck soil and lower BD, MS, Fe₂O₃, Al₂O₃ and Cr. Soil depth influenced Fe₂O₃, MnO, Zn, MS and enzyme activities, while basic soil properties (OM, pH, BD, WHC and P₂O₅) were not changed by soil depth. Heavy metals (Zn, Cr, Cu and Pb) were below upper permissible limits. Copyright © 2010 John Wiley & Sons, Ltd.     

Mineralogical and chemical compositions of the paleosols of different ages buried under kurgans in the southern Ergeni region and their paleoclimatic interpretation

The chemical and mineralogical compositions and the contents and properties of the organic matter were studied in the paleosols of different ages buried under the kurgan group “Kalmykia” in the southern part of the Ergeni Upland. The investigated sequence of soils included profiles developed on the given territory about 5100, 4410, 4260, 4120, 3960, and 600 yrs ago. The background light chestnut soil was also examined. The results of our study showed that the earlier established climate changes in this area during the second half of the Holocene are reflected in the chemical and mineralogical compositions of the soils. These characteristics can be used as indicators of the paleoclimatic conditions together with some petrophysical characteristics, such as the magnetic susceptibility of the soil samples. The study of the mineralogical composition of the clay fraction of the paleosols attests to the transformation of the smectitic phase, accumulation of illites, and destruction of chlorites manifested at different degrees. It is argued that the geochemical indices—CIA, Al₂O₃/(CaO + MgO + K₂O + Na₂O), Rb/Sr, and Ba/Sr—are sensitive to climate changes and reflect the transformation of the mineral soil mass and the soil genesis.     

Ecological testing of ultra-early common wheat forms under various photoperiod conditions

Morphophysiological traits of spring wheat (Triticum aestivum L.) forms are studied in pot and field experiments with 18-, 12-, and 8-h photoperiods. Genes controlling photoperiod sensitivity (Ppd) and growth habit (Vrn) are determined in these forms by means of hybridological analysis and allele-specific molecular markers. Ultra-early forms are valuable parent material for breeding common wheat for early ripening.     

Dissolution of Gibbsite and Its Transformation to Taranakite Depending on the Concentration of Phosphate Anions in the Solution

Structural changes of gibbsite at the binding of phosphate anions from NH₄H₂PO₄ solutions of different concentrations (from 10^–6 to 2 mol P/L) have been studied using an X-ray diffractometer and an electron scanning microscope with a spectrometric microanalyzer. It has been shown that, beginning from a concentration of 10^–3 mol P/L, the binding of phosphate anions has been accompanied by the release of anionic aluminum–phosphate complexes into the liquid phase. The content of these complexes has increased with the phosphate solution concentration and the time of its contact with gibbsite. The treatment of gibbsite with a 1 M phosphate solution for two months has resulted in the pronounced dissolution of the gibbsite crystal surface, accompanied by the formation of ammonium taranakite (ammonium salt of complex aluminophosphoric acid). Successive changes in size and form of the initially formed ammonium taranakite crystal has occurred in a 2 M phosphate solution. The degradation of the layered structure of taranakite and the enrichment of degradation products with phosphorus and nitrogen have been revealed. The significant increase of the P/Al ratios in the degradation products compared to the corresponding ratio in the initially formed taranakite indicates the formation of new phosphate phases resulting from the transformation of taranakite under the impact of free phosphate anions in a high-concentration solution.     

Nonhydrolyzable Part of Soil Organic Matter in Buried and Modern Soils

Eurasian Soil Science - Results of the study of humus composition in about 200 modern soils of different genesis and more than 100 buried Pleistocene and Holocene paleosols have been collected and...