A Soil Water Repellency Empirical Model

The contact angle (alpha) varies nonlinearly with the soil water content (theta(g)) in water-repellent soils; however, a quantitative description of such a theta(g) dependence of alpha is still lacking. Using a dimensionality reduction technique such as dynamic factor analysis (DFA), we managed to identify two common patterns within a scattered data set of a vs. theta(g) measurements performed with the molarity of an ethanol droplet test in 16 soil samples. These two common patterns, derived from the DFA, provided the basis for calibrating a proposed empirical, three-parameter, linear model that described satisfactorily (R-2 > 0.89) an additional alpha-theta(g) data set used for model validation, from 40 soil samples with organic matter contents spanning from 110 to 650 g kg(-1). This offered both scaling and a flexible quantitative description of the soil water content dependence of water repellency.