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The properties of soils affected by salinity and the processes involving degradation of soil structure are relatively well-known. However, the effects of saline and sodic condi-tions on the physical and mechanical properties of soils have been studied to a lesser ex-tent. In this research, the effects of electrical conductivity (EC) and sodium adsorption ra-tio (SAR) of solutions were assessed on soils containing various amounts of organic matter under laboratory conditions. The soils used were collected from the Dasht-e-Naz of Sari region in the north of Iran and contained the same clay type, predominantly Illite. The major difference between the soils was their organic matter content. The treatments con-sisted of applying solutions with definite EC and SAR (two levels of EC: 0.5 and 4 dS/m and three levels of SAR: 0, 5 and 15). With an increase of SAR, the wet aggregate stability (WAS) decreased and the amount of dispersible clay (DC) increased. At a similar SAR, higher EC values were associated with lower DC. The order of average aggregate stability of soils were: virgin soils > soils under continuous cultivation of Festuca > soils under in-tensive cultivation with regular crop rotation > soils under continuous cultivation of Ag-ropyron. The analysis of variance showed significant differences (at 1%) between soil types, soil sampling depths, EC and SAR.

Keywords: Dispersible Clay (DC), Organic carbon, Salt-affected Soils, Wet aggregate stability (WAS)

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