Surface charge characteristics of volcanic-ash-soils from spain. effect of organic matter and mineralogical composition

Abstract

Surface charge characteristics of several Spanish Andosols were investigated. The relationship between these characteristics and the mineralogical composition and organic matter content of the soils were also taken into account. The electrochemical behaviour of the soils was similar to that of many metallic oxides, in which the surface charge is determined exclusively by the activity of potential determining H+ and OH ions in the bulk solution. The ZPC of the soils varies between 3.7 and 5.1 and always remains below the zero point of titration (between 0.6 and 10 meq/100g). These low ZPC values seem to be related to the high content of organic matter in the soils, but no clear correlation between both values has been found. The mineralogical composition and the percentage of amorphous oxides in the soils, on the other hand, had an effect on the charge characteristics. A correlation coefficient (r=0.801) was found between the Al2O3% and ZPC value of the soils.