Saline-Sodic Soils and Dispersion

Only sodium ion (not sodium salts) leads to dispersion of soil particles. And that is related to small ionic size of sodium ion, and its high density of charge per unit circumference and consequently attraction of large number of water molecules. This in turn, results in a large hydration shell surrounding sodium ion. All other ions, that are commonly present in soils, are larger than sodium, hence do not cause dispersion.
Saline soils (that have high electrical conductivity) are harmful for plant growth, because of the high overall salt. High salt content in soil solution desiccates plants by pulling water out of their cells due to high osmotic potential between plant cells and saline soil solution.