Chernozem, also called black soil, regur soil or black cotton soil, is a black-colored soil containing a high percentage of humus (4% to 16%) and high percentages of phosphorus and ammonia compounds. Chernozem is very fertile soil and can produce high agricultural yields with its high moisture-storage capacity. Chernozems are a Reference Soil Group of the World Reference Base for Soil Resources (WRB).

Distribution

The name comes from the Russian terms for black (чёрный čjornyj) and soil, earth or land (земля zemlja). The soil, rich in organic matter presenting a black color, was first identified by the Russian geologist Vasily Dokuchaev in 1883 in the tallgrass steppe or prairie of Eastern Ukraine and Western Russia. Chernozem covers about 230 million hectares of land. There are two "chernozem belts" in the world. One is the Eurasian steppe that extends from eastern Croatia (Slavonia), along the Danube (northern Serbia, northern Bulgaria (Danubian Plain), southern and eastern Romania (Wallachian Plain and Moldavian Plain), and Moldova, to northeast Ukraine across the Central-Chernozem Strip of Central and Southern Russia into Siberia. The other stretches from the Canadian Prairies in Manitoba through the Great Plains of the United States as far south as Kansas. Chernozem layer thickness may vary widely, from several centimetres up to 1.5 metres (60 inches) in Ukraine, as well as the Red River Valley region in the northern United States and Canada (location of the prehistoric Lake Agassiz). The terrain can also be found in small quantities elsewhere (for example, in 1% of Poland, Hungary, and Texas). It also exists in Northeast China, near Harbin. The only true chernozem in Australia is located around Nimmitabel, some of the richest soils on the continent. Previously, there was a black market for the soil in Ukraine. The sale of agricultural land was illegal in Ukraine from 1992 to 2020, but the soil, transported by truck, could be traded legally. According to the Kharkiv-based Green Front NGO, the black market for illegally acquired chernozem in Ukraine was projected to reach approximately US$900 million per year in 2011.

[Distribution of chernozem soils according to the World Reference Base for Soil Resources classification:

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Canadian and United States soil classification

Chernozemic soils are a soil type in the Canadian system of soil classification and the World Reference Base for Soil Resources (WRB). Chernozemic soil type "equivalents", in the Canadian system, WRB, and U.S. Department of Agriculture soil taxonomy:

Theories of Chernozem origin

As seen in the list above, the 19th and 20th-century discussions on the pedogenesis of Chernozem originally stemmed from climatic conditions from the early Holocene to roughly 5500 BC. However, no single paleo-climate reconstruction could accurately explain geochemical variations found in Chernozems throughout central Europe. Evidence of anthropomorphic origins of stable pyrogenic carbon in Chernozem led to improved formation theories. Vegetation burning could explain Chernozem's high magnetic susceptibility, the highest of the major soil types. Soil magnetism increases when soil minerals goethite and ferrihydrite convert to maghemite on exposure to heat. Temperatures sufficient to elevate maghemite on a landscape scale indicate the influence of fire. Given the rarity of such natural phenomena in the modern day, magnetic susceptibility in Chernozem likely relates to control of fire by early humans. Humification can darken soils (melanization) absent a pyrogenic carbon component. Given the symphony of pedogenic processes that contribute to the formation of dark earth, Chernozem summarizes different types of black soils with the same appearance but different formation histories.