Pedogenesis of Chernozems in Central Europe — A review
Introduction
Since Vassilij V. Dokuchaev's investigations in Russia, Chernozems were defined as steppe soils, with their pedogenesis dominated by the soil-forming factors of dry continental climate and steppe vegetation, with carbonaceous parent material, mainly loess, and bioturbation as other prerequisites (Dokuchaev, 1883, Dokuchaev, 1889). Dokuchaev's results for the Russian Chernozems were transmitted to Central European Chernozems (e.g. by Hohenstein, 1919) and his definition was assumed to be universally valid for Eastern and Central Europe, although it was deduced from Russian soils.
But a comparison of the results of several studies concerning the formation of Central European Chernozems to Dokuchaev's definition of a Chernozem as a steppe soil showed that there are obvious discrepancies. By definition, Chernozems should be zonal soils, preserved under continental steppe conditions. However, continental climate occurred during the Late Glacial (c. 15000–11500 BP) but there is no evidence for the presence of Chernozems in Central Europe in the Late Glacial (Rohdenburg and Meyer, 1968, Ikinger, 1996). First evidence for fully developed Chernozems originate from the Early Holocene (c. 11500–5500 BP; Pre-Boreal to Atlantic) when warmer climate and forest vegetation dominated the Central European loess-belt.
The purpose of this review is to highlight the most important literature on Chernozems in Central Europe published since the 1920s. We did not discuss the Russian Chernozems, because this would exceed the limits of this paper. We also exluded black soils formed with a steady water supply, like Gleyic Chernozems and Gleyic or Stagnic Phaeozems. In this review, we want to discuss the following questions: (1) What is the definition of Chernozems, and (2) where do we find them? (3) When did Central European Chernozems form, and (4) is their formation bound to a certain climate and vegetation? (5) Which factors control conservation and degradation of Chernozems? (6) Are there unconsidered factors that influence Chernozem formation or their soil properties?
We focus on different soil forming factors potentially dominating the pedogenesis of Chernozems in Central Europe, i.e. time, vegetation, climate and, potentially overlooked so far, fire and man. We want to point out that there is no generally accepted consensus on the formation of Chernozems in Central Europe.
Section snippets
What is a Chernozem? Definitions and systematics
The World Reference Base for Soil Resources (FAO/ISRIC/ISSS, 1998) defined Chernozems as soils with mollic or chernic horizons of at least 20 cm and with a chrome of ≤ 2 for substrate finer than sandy loam or ≤ 3.5 for sandy loam or coarser substrate, respectively. Chernozems should contain concentrations of secondary carbonates starting with in 50 cm of the lower limit of the A horizon but at least within the top 200 cm, they should lack a petrocalcic horizon or secondary gypsum between a depth
Where do we find Chernozems and Phaeozems in Europe?
The distribution of Chernozems and Phaeozems in Central Europe is shown in Fig. 2. The Eurasian Chernozem occurs in an area stretching from the Southern Urals to the Ukraine, passing through Moldavia and narrowing in the Danube basin (FAO-UNESCO, 1981, Bronger, 2003). Chernozems were characterized in Romania (Schönhals et al., 1982), Bulgaria (Koinov, 1968), in the Alföld and Banat regions in Hungary (Szücs, 1963), in the Vojvodina (Neigebauer et al., 1983), in Bohemia and Moravia (Hrasko et
Time — When did Central European Chernozems form?
Late Glacial and Early Holocene were discussed as possible times of Central European Chernozem pedogenesis (Kopp, 1965, Ehwald et al., 1999). Stratigraphical methods and radiocarbon dating were used to determine the age of a soil. But methodological problems, and because the ages vary over time, absolute ages are still not known.
Vegetation — Formation under forests or after all still a steppe soil?
Dokuchaev, 1883, Dokuchaev, 1889 concluded that Russian Chernozems formed under continental climate and steppe vegetation. Earlier, it was assumed that they developed under moist and wet conditions like Stagnic or Gleyic Chernozems (WRB-FAO; Bell and McDaniel, 2000). Dokuchaev stated that the soil forming factors interact and that climate would not be the dominating factor (Ehwald, 1984), and steppe vegetation was considered a main prerequisite for the formation of Chernozems (Laatsch, 1934,
Climate and relief — Conservation and degradation of Chernozems
Based on the assumption that Chernozems are steppe soils, a model was developed concerning conservation and degradation affected by climatic changes (e.g. Rau, 1968 for Central Germany). Chernozems formed under steppe conditions were expected to stay preserved in regions with a balanced or negative water balance. In Central Europe, this would be in geographical regions with a mean annual precipitation of less than 500 mm, as stated by Meyer (1926). With increasing precipitation and leaching,
Charred organic matter as colouring agent
Up to now, the dark brown to black colour of Chernozem A horizons was attributed to humic acids that cover clay minerals or are bound between the layers of clay minerals. These resistant clay–humus-complexes remained in the argic subsoil horizons of leached and degraded Chernozems or Phaeozems (Greenland, 1971, Gebhardt, 1971, Rochus, 1979).
In contrast, some black soils seemed to inherit their dark colour from charred organic carbon or black carbon. The term black carbon describes a continuum
Conclusions
This review on the pedogenesis of Central European Chernozems revealed that the processes and factors affecting Chernozem formation and conservation are diverse. Published results often conflict with the definition of Chernozems as steppe soils formed under continental climate.
We found that: (1) No absolute age and time of Chernozem pedogenesis could be stated. Stratigraphical records and radiocarbon data showed that the formation in the Late Glacial, when steppes actually occurred in Central
Acknowledgements
We wish to thank Stefan Pätzold and Gerd Welp for their helpful comments on a previous version of the manuscript and gratefully acknowledge the valuable contributions of two anonymous reviewers.
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