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Abstract Evaluation of the water content‐suction relation applicable to field soil horizons that differ widely in texture was considered. Except for coarse‐textured, organic matter‐deficient horizons, it is concluded that soil water retention of sieved samples is significantly modified and does not represent the natural soil volume. Water content‐suction data from measurements on carefully procured core samples of each horizon of a Typic Hapludult adequately represent their water retention characteristics. Using appropriate water content‐suction data, the hydraulic conductivity‐water content relation calculated by published procedures was compared with hydraulic conductivity measured on similar samples by a transient outflow procedure. The calculated hydraulic conductivity‐water content relations for coarse grained systems or systems having a relatively narrow range of pore size and well‐defined bubbling pressure was sufficiently accurate for many purposes. However, to obtain a useful evaluation of the unsaturated hydraulic conductivity of fine‐textured horizons with a very wide range of pore size and a poorly defined bubbling pressure, the Marshall or Millington and Quirk methods had to be matched at a water content in the 0.1‐ to 0.3‐bar range. Indiscriminate use of such methods of calculating hydraulic conductivity is inadvisable.
R. R. Bruce (Sat,) studied this question.