زهرا نریمانی

Salinization and solonization are of common processes in the soils of arid and semiarid regions and are serious problem in agricultural development and sustainable use and management of soil and water resources. Now a day, these processes are extremely active in lands around Urmia Lake and the most of agricultural and horticultural lands around Urmia Lake have been destructed due to these processes and as a result excluded from crop production cycle. In this study physical, chemical and mineralogical properties and classification of six soil profiles in the lands affects by Urmia Lake and two profiles in the lands which unaffected by Urmia Lake were investigated.
The study area has been located at the east of Urmia. Mean annual precipitation and mean annual temperature of this area are 345 mm and 10.83 ºC respectively and the soil moisture and soil temperature regims of this area are Dry Xeric and Mesic respectively. In order to perform this investigation, the position of six soil profiles in saline-sodic soils in the west of Urmia Lake were determined in which include nearly all of saline-sodic soils of this area. In order to control the effect of management and land use, all of soil profiles were dug in non agricultural lands. Additionally, two soil profiles in nonsaline-nonsodic soils which had the same conditions as saline-sodic soils were studied as representative profiles. Soil sampling was done from all of characteristic horizons and the physic-chemical properties of soils were determined using standard methods and soils were classified according to the last version of soil taxonomy. In order to mineralogical studies, pure clay samples were studied using SHIMADUZ XRD 600 diffractometer with 0.4 second time delay in 2θ angels between 2-30 degree, using beam source of Cukα with 30kv voltage and 30 mili ampere.
The results of this study revealed that the soils around Urmia Lake have been extremely salinized and alkalized and their physico-chemical and mineralogical properties were greatly different in comparison with the soils that have not been affected (or less affected) by Urmia Lake. According to the results, saline- sodic soils had more clay content, electrical conductivity, cation exchange capacity, exchangeable sodium and soil evolution, whereas, the content of organic carbon and calcium carbonate equivalent were higher in nonsaline-nonsodic soils. Clay mineralogical investigations revealed that the clay minerals in both groups of saline-sodic and nonsaline-nonsodic soils were mainly smectite, illite, kaolinite, chlorite, vermiculite, hydroxy interlayered vermiculite, mixed layered minerals and quartz. The origin of illite, kaolinite, chlorite, and hydroxy interlayered vermiculite were related to inheritance from parent material, the origin of vermiculite were related to transformation of illite, and smectites have been formed under inheritance from parent material, illite transformation and neoformation from soil solution. It seems that the neoformation is the main mechanism for the formation of smectites in saline-sodic soils. The saline-sodic soils contain more smectite than nonsaline-nonsodic soils and it might that the formation of smectite via neoformation is the main cause of high amounts of smectite in studied saline-sodic soils.
Accordingly, salinization and solonization which have been resulted from Urmia Lake, have caused mineralogical changes in soils around Urmia Lake and presence of more smectite in saline-sodic soils. Differences in morphological and physico-chemical properties of studied soils have been lead to extreme variety in their classification, in which these soils were classified in three orders, three suborders, four great groups and four subgroups.