Hysteresis in soil water characteristics as a key to interpreting comparisons of laboratory and field measured hydraulic properties

This study is mainly aimed at assessing the adequacy of laboratory-based soil hydraulic characterization carried out on undisturbed cores for reproducing the in situ soil hydraulic behavior. Assuming that the laboratory sample size is a representative elementary volume (REV) for a single horizon of the soil profiles examined, the analysis of the hysteretic features of the soil water retention function is used to explain the differences observed in the constitutive soil water relationships as obtained from either laboratory or in situ experiments. Because the wetting procedures differ in laboratory and in field experiments, it is argued that the difference in the obtained hydraulic characteristics is the result of different hysteretic paths. From the comparison of measured hydraulic conductivities we deduce that field and laboratory retention curves are a part of the same hysteresis loop. In such a context the field hydraulic functions can be derived from the laboratory functions using the maximum water content (i.e., at zero pressure head) and air entry value measured in the field. It is shown that the field parameters identified from the measurements in the early phases of the field test are sufficient to reliably describe field hydrological behavior.