Assessment of soil water repellency (SWR) was conducted in the decomposed organic floor layer (duff) and
in the mineral soil layer of two Mediterranean pine forests, one in Italy and the other in Spain, by the widely-used water
drop penetration time (WDPT) test and alternative indices derived from infiltration experiments carried out by the
minidisk infiltrometer (MDI). In particular, the repellency index (RI) was calculated as the adjusted ratio between
ethanol and water soil sorptivities whereas the water repellency cessation time (WRCT) and the specifically proposed
modified repellency index (RIm) were derived from the hydrophobic and wettable stages of a single water infiltration
experiment. Time evolution of SWR and vegetation cover influence was also investigated at the Italian site. All indices
unanimously detected severe SWR conditions in the duff of the pine forests. The mineral subsoils in the two forests
showed different wettability and the clay-loam subsoil at Ciavolo forest was hydrophobic even if characterized by organic
matter (OM) content similar to the wettable soil of an adjacent glade. It was therefore assumed that the composition
rather than the total amount of OM influenced SWR. The hydraulic conductivity of the duff differed by a factor of 3.8–
5.8 between the two forested sites thus influencing the vertical extent of SWR. Indeed, the mineral subsoil of Javea
showed wettable or weak hydrophobic conditions probably because leaching of hydrophobic compounds was slowed or
prevented at all. Estimations of SWR according to the different indices were in general agreement even if some discrepancies
were observed. In particular, at low hydrophobicity levels the SWR indices gathered from the MDI tests were able
to signal sub-critical SWR conditions that were not detected by the traditional WDPT index. The WRCT and modified
repellency index RIm yielded SWR estimates in reasonable agreement with those obtained with the more cumbersome RI
test and, therefore, can be proposed as alternative procedures for SWR assessment.
This study explored the effect of soil water repellency (SWR) on soil hydrophysical properties with depth. Soils were sampled from two distinctly wettable and water repellent soil profiles at depth increments from 0–60 cm. The soils were selected because they appeared to either wet readily (wettable) or remain dry (water repellent) under field conditions. Basic soil properties (MWD, SOM, θ v) were compared to hydrophysical properties (Ks, Sw, Se, Sww, Swh, WDPT, RIc, RIm and WRCT) that characterise or are affected by water repellency. Our results showed both soil and depth affected basic and hydrophysical properties of the soils (p<0.001). Soil organic matter (SOM) was the major property responsible for water repellency at the selected depths (0–60). Water repellency changes affected moisture distribution and resulted in the upper layer (0–40 cm) of the repellent soil to be considerably drier compared to the wettable soil. The water repellent soil also had greater MWDdry and Ks over the entire 0–60 cm depth compared to the wettable soil. Various measures of sorptivity, Sw, Se, Sww, Swh, were greater through the wettable than water repellent soil profile, which was also reflected in field and dry WDPT measurements. However, the wettable soil had subcritical water repellency, so the range of data was used to compare indices of water repellency. WRCT and RIm had less variation compared to WDPT and RIc. Estimating water repellency using WRCT and RIm indicated that these indices can detect the degree of SWR and are able to better classify SWR degree of the subcritical-repellent soil from the wettable soil.