What is Chernozem? The world's rare black earth explained

01/12/2025

Chernozems of Ukraine and beyond are known as fertile black earth, a unique type of soil. These black soils occur in only two regions: North America and Central Eurasia. They rank among the most productive soils on Earth and form the true backbone of the world's grain belts. Their agricultural and ecological value is immense. But what are chernozems and why are they so rare? What causes the unusual build-up of humus? And what roles do climate, vegetation, and underlying geology play? These exceptional black soils form indeed only under a very specific set of conditions.

By Kathelijne Bonne. Support GondwanaTalks through a one-time or recurring donation.

Soil formation is a complex process, and the genesis a chernozem requires a perfect convergence of favorable factors. Just as a delicious dish cannot be prepared without the best basic ingredients, a chernozem simply cannot form unless certain conditions are met.

Black earth of a chernozem soil.

Humus and the real black gold

Chernozems are special because they contain abundant humus. Humus is the stuff that makes soil on Earth unique; it is only found on our planet as far as we know. Other planets may show signs of soil formation, but none contain humus. If humus were ever detected on another planet, it would make global headlines. Black earth is the real black gold.

A few posts on GondwanaTalks have already been dedicated to chernozem soils, especially in relation to the war in Ukraine and how bombs and munition damage soils (though the earth has ways to fight back), as well as in the context of the Dust Bowl in the United States, where similar soils succumbed to wind erosion but were largely restored through recovery programs.

In this article, we ignore disasters and explore the following: What are chernozems? And which conditions are indispensable for their genesis?

No good bread without good soils. Bread is made from grains, and grains are grasses—plants that grow best in steppe climates where black soils can form.

How do Chernozems form?

Chernozems develop only when vegetation, climate, and geological aspects are synchronized. The process begins in vast open grasslands and steppe regions of the world, where plants produce large amounts of organic matter every year, creating a high turnover of biomass. When grasses die each year, their deep root systems and aboveground remains accumulate in the soil. Soil fauna gradually converts this organic material into humus.

Unlike forest soils, where leaves decompose quickly above ground and humus accumulates mainly at the surface, the deep rooting of steppe grasses enriches the entire topsoil. This produces a thick, dark, humus-rich horizon that can reach over a meter in depth, sometimes much more.

Good old earthworms and other fauna mix this material intensely, moving it around and distributing it all the way throughout the soil, creating the homogenous, crumbly, airy structure that defines chernozems.

Grassland biomes emerge and thrive only in certain climates, a climate that ensures that the humus does not leach away or decay too quickly.

Wheat grows exceptionally well on the black soils typical of grasslands.

The perfect climate for black chernozem soils

The climate in which chernozems can exist is narrowly defined, neither too dry nor too wet. There must be enough rainfall to sustain grasslands, but not so much that forests take over or that rain leaches humus and minerals from the soil. Too little moisture results in scarce vegetation; too much causes humus to break down rapidly and favours other types of ecosystems.

Exactly between these extremes – in the semi-arid, temperate zones of Eurasia and North America – black soils like chernozems thrive. Seasonal contrasts, with cold winters and warm summers, slow down decomposition and promote the formation of a stable humus layer, a process that takes centuries to millennia. Other soils contain humus too, but usually far less than chernozems.

Wheat.

Loess: essential for chernozems

An unexpectedly crucial factor is what lies beneath, that is not the soil itself, but the geological material underlying it. Many chernozems lie atop thick deposits of loess: fine, wind-blown dust laid down during the ice ages. Loess is rich in minerals, holds water well, and is easy for roots to penetrate because it is very loose and airy, making it an ideal parent material for black earth. Loess is typically calcareous, as is limestone – another substrate on which chernozems can form.

This ideal combination of steppe vegetation and climate on top of a loose, calcareous sediment like loess, is the key formula for chernozems to emerge.

Where are the chernozems of the world? Global distribution of black earth

Ukraine chernozems

Ukraine contains about 25% of the world's chernozem soils. Its famous black earth belt forms the backbone of European grain production and has earned the country the nickname "the breadbasket of Europe." Central and eastern Ukraine host especially deep chernozem profiles.

Chernozems of Russia and the Volga Region

East of Ukraine, the chernozem belt continues into southern Russia, around cities such as Kursk, Belgorod, and Voronezh—some of Eurasia's most important agricultural regions.

Kazakhstan: The Central Asian Steppe

Northern Kazakhstan features extensive chernozem zones, natural extensions of the Eurasian black-earth belt thanks to its steppes, loess deposits, and continental climate.

Chernozems in Central and Eastern Europe

Hungary, Romania, Serbia, Bulgaria, and Moldova all have smaller but highly fertile pockets of chernozems that historically served as major agricultural centers.

Black soils and chernozems in North America

The North American counterparts of chernozems are found in the Canadian Prairies and the U.S. Great Plains. Classified as Mollisols, they closely resemble Eurasian black earth in composition and fertility.

Black soils in Argentina

Argentina's pampas hold humus-rich soils that are similar to chernozems but are classified (as per the WRB classification) as phaeozems.

Humus gives soil its dark to black color (Jan Kroon, Pexels).

Tectonics and time

Chernozems form only under conditions that rarely coincide. Grasslands must persist long enough for organic matter to accumulate. The climate must be stable, with just the right amount of precipitation.

A stable environment is a requirement for erosion to remain limited so that the soil profile can deepen over time. This sum of unique conditions explains why fertile black earth is not so widespread.

Because they require long time spans and minimal erosion, chernozems develop best in flat or gently rolling landscapes. They do not form on steep slopes or in mountains, where erosion resets the landscape over and over again. Plate tectonics therefore influences where chernozems exist—not at active plate boundaries with jagged relief, but in the quiet interiors of continents.

Black soils, food and climate

Chernozems and related black soils (such as kastanozems and phaeozems – which occur in small areas of Catalonia) are crucial for global food security. Their exceptional fertility underpins a large share of grain production in Eurasia and North America. Grains are grasses, which thrive in grassland ecosystems where black soils naturally occur. Black soils also store large amounts of carbon, making them equally important for climate mitigation.

Unfortunately, black soils have weak spots. Intensive agriculture, wind erosion, and climate change threaten their unique properties. Chernozems take centuries to form but can be destroyed within years

Black earth (photo: Axel Hindemith, Wikipedia).

Chernozems elsewhere?

Chernozems also appear outside the two major black earth belts described above, but only in small pockets, for example in Brazil, Australia, and parts of Africa.

Other soil types also accumulate large amounts of organic matter, such as Histosols in peatlands, but they have a completely different origin.

All of them, however, are irreplaceable and play a role in both food security and climate mitigation.

----

A completely different palette of soils can be found on the Canary Island of Fuerteventura. Perhaps steppe-like soils once existed there, but not anymore. Wind erosion was a major culprit during the Dust Bowl—though human over-plowing made things far worse. In Spain, soil erosion driven by drought, severe storms, and agriculture is a growing concern. One can only hope it won't lead to a new dust disaster. Catalonia is a patchwork of soil types, from shadowy mountain soils in the Pyrenees to gypsum-rich soils and gleysols in other biomes. Also explore what soil salinization is, how it spreads, and what can be done about it.

Keywords: chernozem, chernozem soil, what is chernozem, black earth, black soil, chernozem ukraine, chernozem where, chernozems global, what are chernozems, what is a chernozem, black earth where