ABSTRACT
Between the humid tropical zones and the temperate zones we see regions with relatively dry climates where the soils are red or at least have a red B horizon. The ancients used to call them: Terra rossa or sometimes Ferretto (Italy). The process leading to their differentiation is termed rubefaction (rubification or reddening). They belong to different taxa in classifications but they have dynamics of iron in common (Yaalon 1997). All categories together they cover at least 200 million ha in the world.
