Determination and Characteristics of Surface Charge of Soils in Central and Southern China

He Jizheng\ Liu Dongbi\ Liu Fan\ Li Xueyuan (Huazhong Agricultural University, Wuhan 430070)

positive and negative charge amount,point of zero charge(PZC), point of zero net charge (PZNC), determination method,variable charge soil

Positive and negative charge amount, point of zero charge(PZC) and point of zero net charge (PZNC) of soils in central and southern China were studied on the basis of comparison of methods for the determination of PZC. Results showed that: (1)Salt titration potentiometric titration(STPT) method was recommended for routine analysis of soil PZC, for it could provide more information than salt titration(ST) method, and was less laborious and sample consuming. (2)The Fe and Al oxides were the principal carriers of soil positive charge, among which non crystalline Fe and Al oxides played an important role. (3)Soil negative charge includes permanent negative charge and variable negative charge. Soil contained mainly permanent negative charge at low pH, and δp (pH=PZC), CECK(pH=4.0) and ECEC could all show the relative magnitude of the permanent negative charge of soils. For natural soil samples the permanent negative charge was to some extent blocked by Fe and Al oxides, and the blocked amount was mainly related to the content of non crystalline Fe and Al oxides and of 2∶1 type clay minerals. Soil variable negative charge increased with increasing pH. (4)Fe and Al oxides were the main factors affecting soil PZC and PZNC. Soil PZC and PZNC decreased obviously or even vanished after DCB treatment. Soil PZNC was more greatly affected by the content of Fe and Al oxides than by the clay minerals. Soil PZNC was more greatly affected by the content of Fe and Al oxides than soil PZC.