SURFACE CHARGE BEHAVIOR OF SOIL AT ZAWITA LOCATION, DUHOK PROVINCE, KURDISTAN- IRAQ
The study area was located in Duhok governorate, Kurdistan, Iraq. Two pedons were dug with specified horizons and eight soil samples were collected. The pH values indicated slightly alkaline, and non-saline soils. Exchangeable cations were concentrated at the surface and subsurface horizons and low concentration in deep horizons, and exchangeable calcium has a high value compared with the other exchangeable cations. CEC values of soil (12.23- 44.04Cmolc.kg-1) were less than CEC values of clay (40.78-60.36 Cmolc.kg-1). Total and active carbonate ranged between (159.5-359.9 g.kg-1) and (35.0-205.0 g.kg-1) respectively and vertical distribution of total and active carbonate increased downward of pedons. Organic matter was directly decreased towards the depth of soil pedon and ranged between (6.0- 63.3 g.kg-1). The studied soils were clay loam, silty clay to sandy loam texture. Potentiometric titration curves are divided into two groups, in the first group, three curves intersect at a specific point that expresses the zero point of charge (ZPC), whereas in the second group intersect two curves at a specific point. The pH value of ZPC in soil samples (4, 6, and 8) was different from the ZPT. It is not possible to determine ZPC for all study samples and the ZPC positions that were identified have pH (7.4, 7.8, and 8.2). Can be concluded that most ZPT was located in an acid medium, and ZPC was located in an alkaline medium.
surface charges, zero point of charge, zero point of titration, mineral composition.