A. Heidari - Department of Soil Sciences, College of Agriculture and Natural Resources, University of Tehran, Tehran, Islamic Republic of Iran.
Sh. Mahmoodi - Department of Soil Sciences, College of Agriculture and Natural Resources, University of Tehran, Tehran, Islamic Republic of Iran.
M. H. Roozitalab - Agricultural Research and Education Organization, Tehran, Islamic Republic of Iran.
A. R. Mermut - Saskatchewan Centre for Soil Research, Department of Soil Science, University of Saskatchewan, ۵۱Campus Drive, Saskatoon, Canada.

Considerable information exists in the literature showing that expansive layer silicates are not the only clay minerals present in vertisols. However, the presence of a very high clay content dominated by fine clay, regardless of the clay type, together with the wetting and drying cycle in the soil can also produce a high shrink-swell potential. We studied some vertisols with diverse parent materials and climates from western Iran to investigate the role of parent material and climate on formation of these soils. The vertisols of Fars Province (Southwest Iran) have formed on calcareous sediments with ustic-hyperthermic soil moisture and temperature regimes and a mineralogical composition dominated by a palygorskite-chlorite suite. The vertisols of Lorestan Province (Midwest Iran) are also formed from calcareous sediments under the xeric moisture and thermic temperature re-gime, and contain vermiculite as the dominant clay mineral. In Kermanshah Province, vertisols have formed on limestone or in calcareous sediments. They have xeric-thermic soil moisture and temperature regimes. In Ardebil Province, vertisols are formed on vol-canic sediments, and they have xeric-mesic soil moisture and temperature regimes. All vertisols, except those from Fars Province, are classical ones and include montmorillonite in the clay fraction. Our study shows that the interparticle pore size that is controlled by the size of primary particles, regardless of its nature, contributes to the shrink-swell po-tential in the soils we studied in Iran.

IRAN, Clay mineralogy, Interparticle pores, Palygorskite, Soil climate