Physico-chemical properties and electron microscopic studies of saline and sodic soils in Golestan Province

Golestan Province considered as a major agricultural region, contains a vast area of salt affected soils in the northern parts originated mainly from the near surface water table and/or high evaporation. The present study was performed to investigate the physico-chemical and mineralogical properties of saline-sodic soils and to determine the concentrations of salts, identification of the type of salts and their sources. For this purposes, four profiles were selected and sampled at the north of Gorganrood and south of Atrak river basins based on the available maps and studies at the North and South of Gorganrood. These profiles were located in the different distances (km) from the Caspian Sea. Profiles number 1 and 2 are closer to the sea and the distance increases towards the profiles number 3 and 4. All the routine physico-chemical analyses were carried out on the sampled soil horizons. Profiles 1 and 3 were classified as Aquisalids and profiles 4 and 2 classified as Haplosalids and Cambids based on the Soil Taxonomy. In WRB system all of the profiles except profile number 2 that is classified as Cambisols, are classified as Solonchaks. To identify the types of salts, at first XRD analysis was carried out on the powder sample and then SEM/EDS analyses was done. Gibbs chart was used to determine the source of these salts. The salts identified by XRD analyses included gypsum, halite, hexahydrite, epsomite and mirabilite. Gypsum in the profiles was found at the surface and subsurface horizons in the form of lenticular crystals. Halite was also present in the profiles at the both surface and subsurface horizons. Epsomite in profile 1 was observed at the surface and in profile 3 at the subsurface horizons. Mirabilite was observed only in profile number 1 at the surface horizon. The source of these salts in these zones based on the results of the cation and anion analyses of the available ground and surface water and using the Gibbs modeling was recognized as evaporate minerals.