Effects of Electrical Conductivity and Sodium Adsorption Ratio of Water on Aggregate Stability in Soils With Different Organic Matter Content

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 conditions on the physical and mechanical properties of soils have been studied to a lesser extent. In this research, the effects of electrical conductivity (EC) and sodium adsorption ratio (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 consisted of applying solutions with definite EC and SAR (two levels of EC: 0.5 and 4 dS/mand 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 intensive cultivation with regular crop rotation > soils under continuous cultivation of Agropyron. The analysis of variance showed significant differences (at 1%) between soil types, soil sampling depths, EC and SAR