Click to enlarge. Chernozemic soils have surface horizons darkened by organic matter accumulation. A chernozemic A horizon must be at least 10 cm thick and be dark in colour. They are generally found under grassland communities or grassland-forest communities with associated shrubs and forbs. The region dominated by Chernozemic soils has mean annual soil temperatures > 0°C but usually < 6°C and experiences water deficits in most growing seasons.