Water vapour adsorption on water repellent sandy soils

Abstract

Soil sorptivity is considered a key parameter describing early stages of water (rain) infiltration into a relatively dry soil and it is related to build-up complexity of the capillary system and soil wettability (contact angles of soil pore walls). During the last decade an increasing water repellency of sandy soils under pine forest and grassland vegetation has been frequently observed at Mlaky II location in SW Slovakia. The dry seasons result in uneven wetting of soil and up to hundredfold decrease in soil sorptivity in these vegetated soil as compared to reference sandy material, which was out of the reach of ambient vegetation and therefore readily wettable. As far as water binding to low moisture soils is governed by adsorption processes, we hypothesized that soil water repellency detected by water drop penetration test and by index of water repellency should also influence the water vapour adsorption parameters (monolayer water content, W m , specific surface area, A, maximum adsorption water, W a , maximum hygroscopic water M H , fractal dimension, D S and adsorption energies, E a ) derived from BET model of adsorption isotherms. We found however, that the connection of these parameters to water repellency level is difficult to interpret; nevertheless the centres with higher adsorption energy prevailed evidently in wettable materials. The water repellent forest and grassland soils reached less than 80% of the adsorption energy measured on wettable reference material. To get more conclusive results, which would not be influenced by small but still present variability of field materials, commercially available homogeneous siliceous sand was artificially hydrophobized and studied in the same way, as were the field materials. This extremely water repellent material had two-times lower surface area, very low fractal dimension (close to 2) and substantially lower adsorption energy as compared to the same siliceous sand when not hydrophobized.

Effects of conventional moldboard and reduced tillage on seasonal variations of direct CO2 and N2O emissions from a loam Haplic Luvisol

“…RT leads to increased volumes of the macro-and mesopores only in the upper 0-10 cm plough layers, whereas the underlying 10-25 cm layers can be mainly presented by micropores of <0.06 mm (Głąb and Kulig 2008). The macro-and mesopores, in contrast to the micropores, demonstrate higher preferential flows of water after rainfall (Kuncoro et al 2014;Lipiec et al 2006;Orfánus et al 2016;Orfanus et al 2017). Therefore the entire 0-25 cm soil layers in the CT and RT systems can demonstrate favourable and unfavourable moisture and air conditions for soil microorganisms.…”

“…The macro-and mesopores reflect inter-aggregate porosity with a high level of continuity, whereas micropore system includes pores with less continuity and higher tortuosity (Głąb and Kulig 2008;Kuncoro et al 2014;Orfanus et al 2017). Effects of different tillage systems on the soil hydrological properties have been well evaluated but the data were often contradictory (Strudley et al 2008).…”

Condensation of capillary water and decreased surface energy cause increased soil water repellency in sandy soil

“…The threshold soil water content should not to be confused with “critical soil water content” where water‐repellent soil is wettable with further increase in soil water content (Dekker & Ritsema, 1994). In Wong et al (2021), the threshold soil water content occurred at a matric potential of approximately −40 MPa to −20 MPa, where more than a monolayer of water molecules is expected to occur (Hatch et al, 2012; Orfanus et al, 2017). In other non‐soil disciplinary studies, a monolayer of water molecules decreased the surface energy of a surface (Israelachvili, 2011; Janczuk & Zdziennicka, 1994) and Goebel et al (2004) found that SWR is inversely proportional to surface energy.…”

Changes in direct CO2 and N2O emissions from a loam Haplic Luvisol under conventional moldboard and reduced tillage during growing season and post-harvest period of red clover

“…Reduced tillage (RT) can lead to the uniform distribution of meso-and macropores within the plough layer of 0-0.10 m while the 0.10-0.22 m layers are mainly presented by micropores of < 0.06 mm in diameter (Dimassi et al, 2014;Głąb and Kulig, 2008;Lipiec et al, 2006). In the CT system, the soil macro-and mesopores, compared to the micropores, demonstrate higher preferential flows of water after rainfall (Alaoui et al, 2011;Lipiec et al, 2006;Orfanus et al, 2017). As a result, the 0-0.22 m soil layers in the CT and RT systems show temporal differences in favorable and unfavorable moisture and soil air conditions for carbon-and nitrogen-transforming soil microorganisms.…”