Relations between specific surface area and soil physical and chemical properties

The total specific surface area (SA) is a factor that can relate grain-scale properties to macro-scale physical and chemical properties of a porous medium. It is, therefore, advantageous to establish the relationships between SA and general soil physical properties. In this study we investigated the relationship between SA and properties such as soil texture, cation exchange capacity (CEC), volatile organic vapor adsorption, water retention, and saturated hydraulic conductivity. Total specific surface area was highly correlated to the clay-size fraction of the soil and negatively correlated to the soil organic matter (SOM) of the soil. Both the CEC and the soil-water content at −15 bars (the wilting point) were highly correlated to SA. However, a steadily decreasing degree of correlation between SA and water contents at seven increasing matric potentials was seen, suggesting that only the tightly bound water is directly related to SA. Using the measured specific surface area, the soil-water contents at −15 bars were converted into equivalent molecular layers of water coverage. This revealed that the soil-water content at −15 bars was consistently between four and eight molecular layers of water coverage for most soils. This equals the water coverage below which volatile organic chemical vapor/solid partitioning becomes significant. The soil-water content at the wilting point, therefore, seems promising as a simple measure for the lower water content at which Henry's Law and the aqueous/solid partition coefficient can be used to predict VOC adsorption. The Campbell water retention model parameter, b, was highly correlated to the volumetric specific surface area, S0, potentially making S0 useful for predicting the soil-water characteristic curve. The Kozeny-Carman equation was applied to describe the relationship between S0 and the saturated hydraulic conductivity. The equation did not relate well to the measured data. This may be explained by the heterogeneity of all of the investigated soils, whereas the Kozeny-Carman equation was originally developed for structureless soils.