Using the single-ring infiltrometer method to detect temporal changes in surface soil field-saturated hydraulic conductivity

Determining temporal changes in field-saturated hydraulic conductivity (Kfs) is important for understanding and modelling hydrological phenomena at the field scale. Little is known about the sensitivity of temporal change estimates to the method used for measuring Kfs. The objective of this study was to compare temporal changes in Kfs obtained in the surface layer of a clayey soil using two application procedures of the single-ring infiltrometer method. Rings installed permanently at the beginning of a 1.5-year study period (permanent sites, PSs, sample size N=16) and rings installed immediately before conducting the infiltrometer measurement (non-permanent sites, NPSs, N=16) were used on five sampling dates to determine Kfs. The PSs produced estimates of the mean value of Kfs () that were 1.0–3.5 times higher than the NPSs and the differences between the two types of site were statistically significant (P=0.05) on the last three sampling dates. The highest discrepancies between the PSs and the NPSs were observed in relatively wet soil. Changes in during the study period were more appreciable in the NPSs (ratio between the maximum and minimum values of ) than in the PSs (ratio=2.6). It is suggested that the side effects of ring insertion induced lower Kfs values in the sampled soil volumes of the NPSs than of the PSs, because the time interval between ring insertion and infiltrometer application was short for all the NPS experiments while it increased during the study period for the PS experiments. For the PSs, soil structure re-organisation processes had more time to occur after soil disturbance (i.e. compaction, macrostructure collapse) caused by ring insertion. Using PSs was recommended to increase the representativeness of the Kfs data collected during a relatively long period.