According to the results of the study of soils in the Northwest of the Black Sea region, it is determined that here, in the profile of vorony-calcic and calcic Chernozems, both residual and weak alkalinity are manifested. It was found out, nowadays, in the national soil science, there are no clear criteria for the selection of sodic soils and for the determination of their alkalinity degree. Furthermore, there is also the question of the differentiation of the actually sodic and residual-sodic soils. It has been established that on the territory of the Northwest of the Black Sea region polygenetic soils – vorony-calcic and calcic Chernozems weakly and residual-sodic were formed and the diagnostics of their classification and taxonomic position for the moment is rather ambiguous. The diagnostic of the alkalinity degree of vorony-calcic and calcic Chernozems in the Northwest of the Black Sea region was carried out in four methodological approaches. It was established, that it is impossible to carry out precise and unambiguous diagnostics of the alkalinity degree of soils of the territory of the study according to existing methods. Thus, the sodic and residual-sodic soils, according to classification of 1977, are almost entirely positioned as weakly sodic in accordance with the “Field determinant of soils”. In turn, taking into account the Novikova approach, the status of these same soils varies from non-sodic to solonetzes according to the degree of illuviation, the final diagnosis of which, however, contradicts the low content of exchangeable sodium. An integral approach to the determination of the alkalinity degree of soils is proposed, which is based on the chronological features of the course and direction of the sodification process. According to this approach, if the alkalinity of the studied soils is relict, its degree should be diagnosed by the illuviation of silt and by the content of exchange Na+ (Ni> 8 %, Na+<3 % – residual-sodic soils, Ni> 8 %, Na+ ≥ 3 % –sodic soils).In turn, in the case of the modern alkalinity, its degree should be determined by the ratio Ca2+/Mg2+ (<4,8) and by the content of the exchangeable Na+ (<3 % – residual-sodic soils, and ≥3 % – sodic soils).
Key words: Chernozems, the alkalinity degree, diagnostic, steppe, the Northwest of the Black Sea region.
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