Using the simplified falling head technique to detect temporal changes in field-saturated hydraulic conductivity at the surface of a sandy loam soil

Abstract Determining temporal changes in field-saturated hydraulic conductivity ( K fs ) is important for understanding and modeling hydrological phenomena at the field scale. Little is known about temporal variability of K fs values measured at permanent sampling points. In this investigation, the simplified falling head (SFH) technique was used for an approximately 2-year period to determine temporal changes in K fs at 11 permanent sampling points established at the surface of a sandy loam soil. Additional K fs measurements were obtained by the single-ring pressure infiltrometer (PI) technique to also compare the SFH and PI techniques. The lowest mean values of K fs , M ( K fs ), were detected in December and January (20.5 ≤  M ( K fs ) ≤ 146.2 mm h −1 ), whereas higher results (190.5 ≤  M ( K fs ) ≤ 951.9 mm h −1 ) were obtained in the other months of the year. The K fs values were higher and less variable in the dry soil ( θ i  ≤ 0.21 m 3  m −3 , M ( K fs ) = 340.6 mm h −1 , CV( K fs ) = 106%) than in the wet one ( θ i  > 0.21 m 3  m −3 , M ( K fs ) = 78.4 mm h −1 , CV( K fs ) = 185%). Both wet and dry soil were less conductive at the end of the study period than at the beginning one but a more appreciable change was detected for the dry soil ( K fs decreasing by 83.4%) than for the wet one ( K fs decreasing by 63.0%). The simple SFH technique yielded K fs results similar to the more laborious and time-consuming PI technique (i.e., mean values differing at the most by a factor of two). It was concluded that (i) the soil water content was an important factor affecting the K fs results obtained in a relatively coarse-textured soil, (ii) the impact of time from the beginning of the experiment on the saturated hydraulic conductivity was larger for a repeated sampling of dry soil than of wet soil and (iii) the SFH technique yielded reliable K fs results in a relatively short period of time without the need for extensive instrumentation or analytical methodology.