Application of minidisk infiltrometer to estimate water repellency in Mediterranean pine forest soils

Abstract

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 (RI m ) 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 RI m 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.

Persistence of water repellency in coarse-textured soils under various types of forests in NW Spain

“…Surface soils under eucalyptus and pine forests have also been associated to high levels of water repellency in Portugal (Doerr et al, 1996(Doerr et al, , 1998Keizer et al, 2005 a, b;Leighton-Boyce et al, 2005Santos et al, 2013;Shakesby et al, 1993), South Africa (Scott, 2000), Australia (Crockford et al, 1991;Doerr et al, 2006), Germany (Buczko et al, 2005(Buczko et al, , 2007, Italy (Alagna et al, 2017), UK (Doerr et al, 2006), USA (Doerr et al, 2009) and SW Spain (Zavala et al, 2009(Zavala et al, , 2014. Usually, soil water repellency under oak forest is less persistent than it is under pine or eucalyptus forest (Alanis et al, 2017;Zavala et al, 2009Zavala et al, , 2014.…”

Effect of vegetation and its succession on water repellency in sandy soils

“…In the third method of estimating the repellency index, the water sorptivity S wh for water‐repellent state of soil and the water sorptivity S ww for nearly wettable state of soil were estimated, respectively, from the less steep and steeper parts of hockey‐stick‐like relationship (Figure ) and used to calculate a modified repellency index RI m (Alagna, Iovino, Bagarello, Mataix‐Solera, & Lichner, ; Sepehrnia, Hajabbasi, Afyuni, & Lichner, ).…”

“…ww for nearly wettable state of soil were estimated, respectively, from the less steep and steeper parts of hockey-stick-like relationship (Figure 2) and used to calculate a modified repellency index RI m(Alagna, Iovino, Bagarello, Mataix-Solera, & Lichner, 2017;Sepehrnia, Hajabbasi, Afyuni, & Lichner, 2016).…”

Application of a water infiltration model for simulating water repellency of humus soil

“…Hence, the volume of water‐conductive pores is lower, promoting a decrease in IR. Following the wetting of hydrophobic compounds, the repellency effect disappears after prolonged contact with water (Filipović et al, 2018), allowing the IR to increase as the WR disappears (Alagna, Iovino, Bagarello, Mataix‐Solera, & Lichner, 2017). Another viewpoint is that any initially postponed infiltration increases after the CA between the water and the soil particles decreases (Bughici & Wallach, 2016).…”