Abstract: Surface wettability of soil-engaging components of terrain machines and tools influences their soil adhesion behaviour considerably. Hydrophobic materials have, in many situations, excellent property of reducing soil adhesion. Wetting behaviour of rough surfaces and chemical unsmoothed surfaces consisting of materials with high surface energy and with low surface energy is different from homogeneous and smooth surfaces.An equation of relationship between contact angles for a liquid on chemical unsmoothed surfaces formed by dispersing particles in the matrix of other materials and intrinsic contact angles of their components has been derived. For chemical unsmoothed surfaces dispersed with Al₂O₃ particles in PA 1010 matrix, measured values of their contact angles fit well with the values calculated by the equation. The effect of a certain content of Al₂O₃ particles on contact angles for liquid on the chemical unsmoothed surfaces formed by dispersing Al₂O₃ particles in the matrix of PA1010 is a little. Hydrophobicity of steel T8 - polysiloxane chemical unsmoothed surfaces is, considerably, enhanced in comparison with steel T8.Wettability of rough surfaces of steel, Al₂O₃ and polymers varies due to surface irregularity and the extent of change of the contact angles depends upon their inherent wettability, that is, wetting behaviour of smooth surfaces of these materials. The greater the difference between their intrinsic contact angles and ninety degrees, the greater the effect of surface roughness on contact angles is.