Click to enlarge Solonetzic soils occur in the same ecozones as Chernozemic soils. These soils are characterized by low (exchangeable) calcium to magnesium ratio. The diagnostic horizon is a Bn (or Bnt), which is very hard when dry and which swells and becomes relatively impermeable when wet. There are four great groups of the Solonetzic order. Three of them represent an idealized evolutionary sequence, which begins with soil with a Bn horizon (Solonetz great group). Sodium-enhanced clay translocation begins, creating an Ae and a Bnt horizon (Solodized Solonetz great group). When the upper Bnt is altered by the weathering processes outlined above, the soils are placed into the Solod great group. In soils formed in parent material high in clay (typically > 60% clay) the Ae/Bnt sequence may be weakly expressed and those soils are classified into the Vertic Solonetz great group.