Chernozem

Worldwide spread of chernozemes

Soil profile of a chernozem

The Chernozem (from Russian чернозём , chernosjom [ t͡ʃɪrnʌˈzjom ]) is a reference soil group of the international soil classification World Reference Base for Soil Resources (WRB), which belongs to the group of humus accumulation soils . It is the zonal soil of the semi-humid to semi-arid long-grass steppes .

Occurrence

Chernozemes are found mainly in the dry middle latitudes in the areas of the long-grass steppes. These lie roughly between the drier (more continental) area of ​​the Kastanozeme and the more humid (somewhat more oceanic) area of ​​the Phaeozeme . In the northern hemisphere, these are the Eurasian steppe (southern Ukraine , southern Russia and Kazakhstan ) and the northern Great Plains (especially Canada ). Aside from the steppes, chernozemes also occur under forest. Large steppe areas were forested in the Early Holocene . Chemical studies in humus (e.g. studies on the alkanes ) show that in many chernozemes part of the humus was already formed in this forest phase (Zech et al., 2014).

Main features

It is named after the deep black color, which results from the very high humus content (often 12–13%). The humus is worked in deeply and homogeneously (up to 1.2 m) by soil diggers ( bioturbation ). The very dark, humus-rich and well-aggregated mineral topsoil horizon is called chernic horizon in the WRB . Because of the low precipitation, the leaching of base cations is only insignificant. Where the seepage water stops regularly, there are accumulations of secondary lime, sometimes in the form of "loess pebbles". Chernozemes have a very rich soil life, favorable pH values and high nutrient contents .

use

Chernozeme belong to the most fertile soils in the world with relatively secure precipitation conditions at the same time. On the soils of the North American prairies and the Eurasian steppe , wheat is mainly produced, but barley and maize are also produced . However, drought events can occur regularly . In large areas, therefore, pasture farming ( cattle ) dominates.

The humus accumulation soils in Germany ( Hildesheimer Börde , Magdeburger Börde and more to the east) are insignificant worldwide, but are of great national importance. In Germany, the maximum possible productivity of a soil is defined on the basis of the yields of the soils in the Magdeburg Börde. In the WRB, depending on the presence of secondary lime, these belong partly to the Chernozemes and partly to the Phaeozemes .

Used sites are prone to soil erosion and overgrazing . Fires are not uncommon in the steppes. They lead to the accumulation of pyrogenic carbon , which contributes to the black color of the chernozemes.

Related soil types

The Chernozem is the zonal soil of the long grass steppe. It has properties that lie between those of the Kastanozems (more continental, drier and milder short-grass steppes) and the Phaeozems (more humid transition between steppe and forest). The topsoils of Kastanozems are less humic and therefore lighter (chestnut brown), somewhat less thick and often heavily interspersed with accumulations of secondary lime. They miss the criteria of the chernic horizon and only meet those of the mollic horizon . In the Phaeozem there is no accumulation of secondary lime due to the wetter conditions (except sometimes at greater depths).

In the German soil systematics there is the class of black earth with the soil types Chernosem and Kalktschernosem . The black earths of the German Soil Systematics are defined by an Axh horizon that is at least 40 cm thick. The WRB's chernic horizon , however, is only 25 cm thick. Chernozemes with a chernic horizon <40 cm do not belong to the black earth , but to various other types of the German soil systematics, e.g. B. to the Pararendzina . For the Chernozeme with a chernic horizon ≥ 40 cm applies:

• Chernozemes of the WRB, which do not have a dominant B horizon, belong to the Chernosemes or the calcareous chernosemes, depending on the depth at which the secondary limestone begins. Conversely, the limestone chernosemes usually belong to the chernozemes, but the chernosemes only if they have secondary limestone at the required depth. Otherwise they belong to the Phaeozemes .
• Chernozeme of the WRB with a dominant Bt horizon belong to the Chernosem parabroun earths in the German soil systematics .

See also

• Black earth

Web links

• Profile photos (with classification) WRB homepage
• Profile photos (with classification) IUSS World of Soils

literature

• IUSS Working Group WRB: World Reference Base for Soil Resources 2014, Update 2015. World Soil Resources Reports 106, FAO, Rome 2015. ISBN 978-92-5-108369-7 ( PDF 2.3 MB).
• W. Zech, P. Schad, G. Hintermaier-Erhard: Soils of the world. 2nd Edition. Springer Spectrum, Heidelberg 2014. ISBN 978-3-642-36574-4 .
• W. Amelung, H.-P. Blume , H. Fleige, R. Horn, E. Kandeler , I. Kögel-Knabner , R. Kretschmar, K. Stahr , B.-M. Wilke: Scheffer / Schachtschabel textbook of soil science. 17th edition. Heidelberg 2018. ISBN 978-3-662-55870-6 .
• AD-HOC Working Group Soil: Soil Science Mapping Instructions , Ed .: Federal Institute for Geosciences and Raw Materials in cooperation with the State Geological Services, 5th edition, 438 p .; 41 figs., 103 tabs., 31 lists, Hannover 2005, ISBN 3-510-95920-5 .