The Study of Physico-chemical and Micromorphological Properties of Gypsiferous-Alkaline Soils in Shoshab area, Hamadan province

The content of gypsum and salts in soil profiles is one of the major challenges in arid and semi-arid region which comprise un-arable lands in Iran and their reclamation need their complete identification. Shoshab region is one of these lands which areas under cultivation reduced due to high salinity and gypsum content. The purpose of this study was to investigate the physico-chemical and micro-morphological properties of gypsic-alkaline soils in this area. Sampling of eight soil pedons were conducted in order to analysis of physical, chemical and micropedological characteristics and soil profiles were classified according to the Keys to Soil Taxonomy. The results showed that soil gypsum and calcite increased with increasing soil depth. The range of soil pH was high and was not affected by the soil depth. The presence of gypsum induced soil texture to  silt and sand fractions. The exchangeable sodium content was more in surface horizons and reduced with increasing soil depth. Micromorphological observations demonstrated hypocoating, coating, loose continuous, dense complete and dense incomplete infilling of gypsum in voids and channels walls. Lenticular, prismatic, and allabasrtin of gypsum crystals were observed in thin sections as well. Lenticular gypsum form was common in all soil thin sections because of the xeric moisture regime in this region. The dominant presence of gypsum and sodium in the soils induced to angular and sub angular blocky micro-structures and the aggregation effect weakened. The crystallites form was the usual observed b-fabric in all thin sections and in some cases identified as undifferentiated b-fabric. Generally, the existing of salt and gypsum in the soils of this area led to unsuitable soil voids and soil structure which is a serious environmental issue and plant growth promoting.  New great group and subgroups of Xerepts (Gypsic Calcixerepts) are suggested to be included in soil Taxonomy based on the properties of the some studied soil pedons.