The soils of steppes and the factors involved in their formation are discussed above
and here only a brief discussion follows. Two types of soils are typical of the steppe and
forest-steppe biomes: chernozems or black soils and kashtanozems or chestnut soils (Table
11.1).
Table 11.1 Zonal soils and vegetation in steppe, forest-steppe, and
semi-desert
Chernozem is one of the most fertile soils on Earth. In Northern Eurasia, chernozems
occupy about 1.9 million km2. Many prominent scientists researched the origin
of chernozem and linked it to the rich herbaceous vegetation typical of steppe and meadow
steppe (Rupreht, 1866; Dokuchaev, 1883; Kostychev, 1937). About 1-2 kg m2 of
dead phytomass is produced annually and about a half of it is contributed by the below
ground parts (Alekhin, 1934; Titlyanova et al, 1983). The organic matter does not,
therefore, accumulate on the surface as litter but is more deeply and evenly distributed
through the soil profile due to the extensive and deep root systems of the plants. The
most favourable conditions for the development of chernozems occur in the southern
foreststeppe where high phytomass reserves coincide with the optimal thermal and moisture
regimes. Thick chernozems dominate in this region. Northwards, a more humid climate
results in leaching of primary minerals and podzolization of soils. Southwards, moisture
deficit causes a reduction in phytomass and the supply of organic matter to the soil,
which leads to the formation of soils less rich in humus and nutrients. The group of
chernozem soils, therefore, consists of a number of subtypes which exhibit a zonal
distribution.
Most fertile are thick chernozems whose humus contents can be as high as 15 per cent
(Table 11.1, Figure 11.3).
Fig. 11.3 Zonal variations in properties of soils
Typical chernozems, which develop in the northern steppe, are distinguished by a less
developed humus horizon and the content of organic matter does not on average exceed 6-9
per cent, although in soils with a fine grain structure it can be as low as 4-5 per cent
(Chesnyak et. al., 1983). Southern chernozems develop under the Stipa-Festuca vegetation
communities in the southern steppes. They are characterized by a smaller thickness of the
humus horizon, which varies between 25 cm and 70 cm. Meadow chernozems develop both in the
steppe and forest-steppe biome in environments with a higher moisture supply, such as
poorly drained watersheds, in topographic depressions, and stream valleys. Meadow
chernozems are very similar to other types of chernozems and the major distinction is that
the content of organic matter in meadow chernozems is higher and, consequently, the humus
horizon has a darker colour.
The changes in soil profile also occur from west to east, reflecting the increasing
aridity and continentality of climate. Thickness of soil cover decreases substantially. In
the Black Sea steppes, soil profiles are about 200 cm deep while eastwards they become
progressively thinner, reaching 50-60 cm in the Transvolga region and 30-40 cm in
Kazakhstan. The occurrence of solonetz-like soils also increases from west to east.
