Appendix A—The role of the pF in the dynamics of soil‐moisture

Abstract

The pF‐concept has no doubt served a useful purpose and has found its way permanently into the literature of soil‐physics. It should be noted, however, that the gradient of the function, p/ρ, (or the gradient of ∫dp/ρ for compressible fluids) enters explicitly into the classical literature of hydromechanics, whereas the other terms in the free‐energy (better, thermodynamic potential) are but remotely involved. The logarithm of ∫dp/ρ likely does not appear at all. BAVER has presented interesting data from which he shows that the percolation‐rate of the soil is correlated with a porosity‐factor defined as the ratio of the non‐capillary porosity to the pF of the flex‐point. Both these quantities are determined primarily by the configuration of the void‐space in the soil, but the permeability is likewise dependent upon the geometry of the void‐space, and it is to be expected, therefore, that these two physical quantities should be correlated.