The extraction of soil water by the suction‐cup method: a review

SUMMARY This article deals with the extraction of soil water using the suction‐cup method and its accompanying problems. This method has become well‐developed over the past 20 years. It allows continuous sampling during any period and, if necessary, at several different depths of a soil profile. The installation of the suction probe is easy and the profile is only negligibly disturbed. Some problems may occur when this technique is used. The spatial variability of the properties investigated is often underestimated and must be clarified by sufficient replication. An important point of discussion is the by passing of water flowing through macropores. The problems of alteration of the sample by the sampling system also deserve attention. These can be the ‘filter effect’ as regards macromolecules and colloids, the sorption of trace substances, and the gas exchange between the sample and the atmosphere of the sampling system.