Ten surface soil samples were selected to represent some soil types of four prominent locations (Tushka, wadi El-Nuqra, El-Kharga and El-Dakhla) in Egypt. The aim was to study the effect of removal of free iron oxides from the whole soil samples and their size fractions (clay and silt) on the cation exchange capacity (CEC) of these soils.
The obtained data reveal that the texture class of the studied surface samples differs from sand to sandy loam with a finer texture in El-Dakhla and a coarser one in El-Kharga. Most of these samples are none to slightly saline with low calcium carbonate and organic matter in some locations. Soil reaction (pH) tends to be moderate to alkaline in most locations.
Based on the morphological, physical and chemical soil properties, the studied soils are classified down to the sub-group level according to Soil Taxonomy as: Typic Torripsamments, Typic Torriorthents and Typic Haplotorrerts.
The removal of free iron oxides from the whole soil samples and their fractions (clay and silt) caused an increase in the cation exchange capacity (CEC) of most studied soils. For the whole soil samples, the highest increase in the CEC was recorded for El-Kharga and the lowest one for Tushka. In most soil samples of Tushka, silt fraction had the highest increase in the CEC, whereas El-Kharga silt fraction gave the lowest increase. Highest values of CEC for El-Kharga soils and lowest ones for wadi El-Nuqra were obtained after removing free iron oxides from the clay fraction of these soils.