Textural features of saline-sodic soils affected by Urmia Lake in the Northwest of Iran

Abstract

The increasing regression of Urmia Lake in the last 30 years has brought about the salinization and sodification of arid soils from the shoreline, which has aggravated land degradation in this area. The objective of this work was to assess the changes in the soils brought about by progressive and fast salinization of the region, and to determine the present- or past character of several textural pedofeatures. We studied the micromorphic, mineralogical and physico-chemical properties of four profiles of saline-sodic soils in the west of Urmia Lake. Most of voids in the studied horizons were mainly vesicles due to structure collapse, besides planes and channels, and their b-fabric were mainly crystallitic micritic and granostriated due to argilloturbation. The main pedofeatures were illuvial clay coatings and also their fragments in the groundmass, clay and silt coatings, calcite accumulations as nodules, infillings and coatings and redoximorphic accumulations as nodules and coatings. Owing to the arid climate and high amounts of calcium carbonate and soluble salts, the illuviation of pure clay in natric horizons probably took place during a wetter past climate during the lower Quaternary. Additionally, based on high values of exchangeable sodium, ESP and SAR, we believe that the high values of exchangeable sodium are the responsible for the structural collapse, dispersion and translocation of fine material (clay and silt) at varying distances within the soil profile. Alkalinisation is likely to proceed from evaporation of the supersaturated waters of Urmia Lake through carbonate precipitation and smectite formation, increasing ESP and changing previous argillic horizons to natric horizons. Increase of organic matter through the application or organic amendments seem to be the best strategy for their reclamation.