Development of a universal microinfiltrometer to estimate extent and persistence of soil water repellency as a function of capillary pressure and interface chemical composition

Abstract

Microinfiltrometers to assess soil water repellency (SWR) are limited to small tension ranges and have different technical setups, hindering a comparison between results from different laboratories. Hence, a microinfiltrometer which considers various aspects like extent and persistence of SWR is needed. The technical update suggested here uses glass tubes (e.g., 3 mm inner diameter), a fabric of mesh size 15 µm around the tip to enable good contact between soil surface and tip, ultrapure degassed water, and an evaporation protection for tip and reservoir during long-term infiltration. The adjustment of a continuous range of pressures and tensions (i.e., +0.5 to –40 cm) was done using glass tubes of various lengths connected to the tip. Three soil samples with initial contact angles, CA, of 18°, 62°, and 91° after 25°C treatment were additionally treated at 80°C to increase SWR persistence and CA. The soil particle interface chemical composition was determined by X-ray photoelectron spectroscopy (XPS). The hydrophysical properties evaluated included water and ethanol sorptivity as well as very important aspects of SWR, i.e. water drop penetration time, water repellency cessation time, repellency index, and modified repellency index. The results derived from the technically modified microinfiltrometer setup showed consistent differences between initial wettability and the water repellency cessation time as a parameter describing the development of SWR with time. The interface O/C ratio as derived from XPS data was negatively correlated with CA (p <0.05), thus proving the close relationship between interface chemistry and wettability. Our findings illustrated a strong positive correlation (R2 = 0.99, p < 0.05) between sorptivity and O/C ratio under –2 cm tension which can be considered as the universal tension for different aspects of SWR.

Variability of topsoil hydraulic conductivity along the hillslope transects delineated in four areas strongly affected by soil erosion

“…Pressure head was always set at the value of -2 cm according to Watson and Luxmoore (1986) as limit between gravitational and capillary pores. This value of pressure head is also standardly set when the various mini disk infiltrometers are used to evaluate soil water repellency (e.g., Fér et al, 2020;Lichner et al, 2020;Sándor et al, 2021;Sepehrnia et al, 2020). The close contact between the carefully levelled soil surface and disk was ensured by a 1 mm layer of the same soil, sieved through a 2-mm sieve, as proposed by Kodešová et al (2010Kodešová et al ( , 2011.…”