Structural features of smectite components in profiles of forest-steppe soils are investigated by X-ray-diffraction. The basal diffraction spectra of oriented preparations from the <2.5 µm fraction in the Mg-form were recorded in the air-dry state and after saturation with ethylene glycol, in the K-form in the air-dry state and after heating at 300 and 500 C, in the Li-form after heating at 300 C and saturation with glycerine. Semiquantitative X-ray-diffraction analysis has been calculated using Sybilla software (Chevron Energy Technology Company).
Nanostructured compounds of iron in the <2.5 µm fraction from the upper, middle and bottom parts of a forest-steppe soil profiles are investigated by Mssbauer spectroscopy of nuclei 57Fe before and after removal of organic matter from preparations by treatment with H2O2 and NaOCl.
It is experimentally shown, that in actual structure of smectite component in a top and bottom parts of profiles of forest-steppe soils formed on initial vertical uniform parent materials there are no other significant differences, except quantitative and qualitative characteristics of organic matter in the interlayer space of smectite and on the surface of its layers. The solution algorithm is developed for a problem of smectite quantification in profiles of forest-steppe soils in the form of an operating sequence: diagnostic of initial parent material uniformity; smectite quantification in the <2.5 µm fraction by an adsorptive-luminescent method and by thermogravimetric analyses; smectite quantification in the <2.5 µm fraction from parent material by X-ray-diffraction analysis using Sybilla software; updating of smectite quantification in a profile of forest-steppe soil according to adsorptive-luminescent and thermogravimetric analyses. Preparation of samples for the total element analysis and algorithm of geochemical indexes calculation are optimized. It allows to result realistic and natural patterns of weathering indexes as a functions of soil depth, which characterize actual behaviour of major mineral elements in a profile of forest-steppe soils. In experiments with forest-steppe soils it is established, that mechanisms of organic matter stabilization postulated in «zonal model of organo-mineral interactions», in particular, assuming a special role of poorly crystallized and amorphous Fe and Al oxides and hydroxides in the protection of organic matter from chemical oxidation are not universal for all soils.
Work is performed under the grant of RFFR (Russian Fund of Fundamental Research, progect №11-04-0052а)
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