A b s t r a c t. Deformable media which are the objects of interest of agrophysics are distinguished by the fact that they are composed of three phases and each of them clearly pronounce its specific role. Comparing existing theories of deformation and flow of three-phase media, at the very beginning, i.e., at the moment of definition and measurement of stress and strain one can recognize four methods: deterministic, statistical, probabilistic and stochastic method. The best is probabilistic method which is concemed with the formulation of the stress-strain response including microstructural effects that are due to the inherent geometrical and physical properties of structured solids. Most of the significant field quantities involved in the formulation of the material behavior are, by nature, random variables or functions of such variables. The method 'of computer image analysis together with a scanning electron microscope, scanning reflected light microscope and computer tomography are presented. Advantages of this method in comparison to the traditional methods of soil pore size distribution (mercury porosimetry, pF-curves and isotherm of nitrogen desorption) are demonstrated.