Universal constants for scaling the exponential soil water diffusivity?

The exponential form of the soil water diffusivity can be scaled either with the wetting front parameter Φf = xf/t½ or with the sorptivity A0 = F/t½; these variables, which arise in the problem of sorption in a dry soil, are xf the distance to the wetting front, t the time, and F the infiltrated water volume. It is shown that the three constants used in this scaling are not independent and that only one constant is needed.