Evaluation of Gardner-Russo Hydraulic Properties of Soil.

The Guelph permeameter and tension/disk infiltrometers are popular instruments to provide in situ with soil hydraulic properties, i.e. the reciprocal value of the macroscopic capillary length that Gardner used as alpha for linearlizing hydraulic conductivity.  Three decades later Russo and his colleagues introduced a water characteristic curve using Gardner’s alpha.  We investigated the applicability of Gardner’s alpha by comparing with van Genuchten’s hydraulic properties for various textures of soil ranging between loamy sand and sandy clay.  Gardner’s alpha value decreased with increases in clay content whereas root mean square error, RMSE, between hydraulic conductivities of Gardner and van Genuchten increased.  The RMSE between water characteristic curves of Russo and van Genuchten increased with increases in clay content as well.  Gardner’s alpha values could properly represent the hydraulic properties of soils with clay content of approximately <11%, say courser than sandy loam.