Micromorphological Characteristics of Vertisols of Iran, Including Nonsmectitic Soils

Abstract

ABSTRACT Vertisols of Iran occupy about 70,000 ha of arable land. They are located in four provinces mainly: Fars (16,000 ha), as soils on calcareous sediments of lowlands, with a ustic-hyperthermic soil climate; Kermanshah (34,000 ha) and Lorestan (6,000 ha), as soils on calcareous sediments in alluvial plains and on plateaux, with a xeric-thermic soil climate; and Ardebil (11,000 ha), as soils on volcanic parent materials in alluvial plains, with a dry xeric-mesic soil climate. They are classified as aridic gypsiusterts, halic haplusterts, chromic haploxererts, typic calcixererts, chromic calcixererts and vertic calcixerepts. They mostly have a mixed mineralogical composition. Smectite is almost absent in some of the vertisols on calcareous sediments, which have palygorskite and chlorite as dominant clay minerals, especially in the fine fraction. The dominant microstructure in subsurface horizons is a strongly developed angular blocky structure with wedge-shaped peds. The b-fabric is mostly calcitic crystallitic. Decalcified zones show a stipple-speckled b-fabric. The less calcareous soils of Ardebil province have a calcitic crystallitic b-fabric in some parts and a stipple-speckled b-fabric with common granostriation in other parts. Some subsurface horizons contain secondary carbonate accumulations in the form of nodules, coatings, or hypocoatings. Decalcified zones along pores are common in one profile of Kermanshah Province, with associated cytomorphic sparitic carbonate infillings. Fe/Mn hydroxide impregnations are omnipresent, which is an indication of seasonal hydromorphic conditions. Illuvial clay is observed only as thin discontinuous coatings, which are partly juxtaposed on CaCO3 hypocoatings.