Characteristics and Variability of Surface Charge on Ferralosols from a Typical Profile at Leizhou Peninsula

Soils from different layers of a Ferralosol profile collected from Xuwen,Guangdong Province were used to study the characteristics and variability of their surface charge.The results indicated that the cation exchange capacity(CEC) of the soils below B horizon was less than 88 mmol kg-1,and the free iron oxides of the soils was in the range of 140.9-220.3g kg-1.Thus,the soils were typical variable charge soils.The amount of soil positive surface charge and the change of positive surface charge when pH changed by one unit increased with the increase of soil free iron oxides.When pH was less than 4.0,the contribution of soil iron oxides to negative surface charge was very small.While the increase in organic matter led to the increase in the variability of soil negative surface charge in the same pH range.The point of zero salt effect(PZSE) of the soils from the profile were higher than the point of zero net charge(PZNC) of the soils,while both PZSE and PZNC increased with the increase of the free iron oxides in the soils.