Abstract
This study was carried out in three selected areas from North Iraq included (Makhmour, Shikhan and Zakho).these location Varied in annual temperature and rainfall .Nine soil samples were collected from three soil profiles (one soil profile from each location). Clay was separated without using any corrosive acid or base, except sodium acetate in order to remove calcium carbonate. Variable charge (pH-dependent charge) was measured using potentiometric titration. Results from titration curves showed a clear variations in positions of (ZPC) and the amounts of negative and positive charges from different samples. The extent of (ZPC) varies from (pH 4.4-5.8).However the amount of negative varies between(100-180) Cmole/kg. and the positive charge between(150-350) C.mole/kg. These variations in potentiometric titration curves are partially related to the presence of varying amounts of iron oxides and also the variations in type of minerals dominant in clay samples .In addition to that, there is a possibility of the presence of some calcium carbonate in clay that not completely removed by treatments with sodium-acetate.
