Point of Zero Salt Effect: Relationships with Clay Mineralogy of Representative Soils of the So Paulo State, Brazil

The point of zero salt effect (PZSE) is the soil pH value at which the magnitude of the variable surface charges is notchanged due to variations in the ionic concentration of the soil solution. This property influences not only electrochemicalphenomena occurring at the solid-solution interface but also the flocculation degree of the soil particles. In this studywe investigated the relationships between the clay mineralogy and the PZSE values of representative soils of the S?oPaulo State, Brazil. The results confirmed the usefulness of the difference between the soil pH values measured in 1 molL-1 KCl (pHKCl) and in water for estimating the PZSE of tropical soils, except for theones rich in exchangeable Al; furthermore, the ΔpH index was highly correlated with the differencebetween the PZSE and values, reiterating the ΔpH utility for estimating both the signal and the magnitude of thenet surface charge of tropical soils. Finally, correlation and multiple regression analyses showed that the PZSE value ofweathered non-allophanic tropical soils tends to increase and to equal the soil pH due to the weathering-induced kaolinitedestabilization and concomitant Fe- and Al-oxide accumulation.

The point of zero salt effect （PZSE） is the soil pH value at which the magnitude of the variable surface charges is not changed due to variations in the ionic concentration of the soil solution. This property influences not only electrochemical phenomena occurring at the solid-solution interface but also the flocculation degree of the soil particles. In this study we investigated the relationships between the clay mineralogy and the PZSE values of representative soils of the Sāo Paulo State, Brazil. The results confirmed the usefulness of the difference between the soil pH values measured in 1 mol L^-1 KCl （pHKCl） and in water （pHH2O） （2 pHKCl-pHH2O） for estimating the PZSE of tropical soils, except for the ones rich in exchangeable Al; furthermore, the ApH index （pHKC1 - pHH2O） was highly correlated with the difference between the PZSE and pHH2O values, reiterating the △pH utility for estimating both the signal and the magnitude of the net surface charge of tropical soils. Finally, correlation and multiple regression analyses showed that the PZSE value of weathered non-allophanic tropical soils tends to increase and to equal the soil pH due to the weathering-induced kaolinite destabilization and concomitant Fe- and Al-oxide accumulation.