Reaction of soil water repellency to artificially induced changes in soil pH

verfasst von: D. Diehl, J. V. Bayer, S. K. Woche, R. Bryant, S. H. Doerr, G. E. Schaumann
Abstract: Soil water repellency (SWR) is widely thought to be influenced by soil pH, however, few studies have systematically investigated the relationship between these variables. Specifically the hypothesis that the pH may control repellency via changes in the variable surface charge of soil material has not yet been tested. In previous work, methods for changing soil pH have also involved changes in soil moisture, but it has been argued that the potential influence of soil moisture changes needs to be eliminated before the actual relationship between pH and SWR can be isolated. The paper addresses this research gap using a new method, which enables adjustment of the pH of soils with low moisture content via the gas phase and thus involves minimal change in moisture content, allowing the response of SWR to pH changes to be evaluated. The method was applied to 14 soil samples from Germany, The Netherlands, the UK, and Australia, using the water drop penetration time (WDPT) as the indicator of SWR. Additionally, sessile drop contact angles (Θ_sess) were measured on the four samples from Germany and the titratable surface charge of these four soils was measured at selected pH values using a particle charge detector (PCD). Changes in SWR with soil pH were found to be influenced by the density and type of sites able to interact with protons at the available surfaces of organic and mineral materials in soil. The maximum SWR occurred for soil at natural pH and where the charge density was minimal. As pH increased, negative surface charge increased due to deprotonation of sites and WDPT decreased. Two types of behaviour were observed: i) a decrease in repellency with decreasing pH, probably because of a sufficient number of proton accepting surface sites with a significant amount of positive surface charge, ii) no decrease in repellency with decreasing pH in soils with insufficient proton accepting surface sites to develop significant positive surface charge. The data suggest that the availability and relative abundance of proton active sites at mineral surfaces, and those at organic functional groups influence the response of the soil samples to changes in pH. The variety of geographic origins and histories of the soils examined provides a distinction between site specific and more widely applicable soil characteristics of pH dependent SWR.
Organisationseinheit(en): Institut für Bodenkunde
AG Bodenphysik
Externe Organisation(en): Universität Koblenz-Landau
Swansea University
Typ: Artikel
Journal: GEODERMA
Band: 158
Seiten: 375-384
Anzahl der Seiten: 10
ISSN: 0016-7061
Publikationsdatum: 09.2010
Publikationsstatus: Veröffentlicht
Peer-reviewed: Ja
ASJC Scopus Sachgebiete: Bodenkunde
Elektronische Version(en): https://doi.org/10.1016/j.geoderma.2010.06.005 (Zugang: Unbekannt)

BibTeX

@article{dee98b1268e14da7898077abf66b51df,
title = "Reaction of soil water repellency to artificially induced changes in soil pH",
abstract = "Soil water repellency (SWR) is widely thought to be influenced by soil pH, however, few studies have systematically investigated the relationship between these variables. Specifically the hypothesis that the pH may control repellency via changes in the variable surface charge of soil material has not yet been tested. In previous work, methods for changing soil pH have also involved changes in soil moisture, but it has been argued that the potential influence of soil moisture changes needs to be eliminated before the actual relationship between pH and SWR can be isolated. The paper addresses this research gap using a new method, which enables adjustment of the pH of soils with low moisture content via the gas phase and thus involves minimal change in moisture content, allowing the response of SWR to pH changes to be evaluated. The method was applied to 14 soil samples from Germany, The Netherlands, the UK, and Australia, using the water drop penetration time (WDPT) as the indicator of SWR. Additionally, sessile drop contact angles (Θsess) were measured on the four samples from Germany and the titratable surface charge of these four soils was measured at selected pH values using a particle charge detector (PCD). Changes in SWR with soil pH were found to be influenced by the density and type of sites able to interact with protons at the available surfaces of organic and mineral materials in soil. The maximum SWR occurred for soil at natural pH and where the charge density was minimal. As pH increased, negative surface charge increased due to deprotonation of sites and WDPT decreased. Two types of behaviour were observed: i) a decrease in repellency with decreasing pH, probably because of a sufficient number of proton accepting surface sites with a significant amount of positive surface charge, ii) no decrease in repellency with decreasing pH in soils with insufficient proton accepting surface sites to develop significant positive surface charge. The data suggest that the availability and relative abundance of proton active sites at mineral surfaces, and those at organic functional groups influence the response of the soil samples to changes in pH. The variety of geographic origins and histories of the soils examined provides a distinction between site specific and more widely applicable soil characteristics of pH dependent SWR.",
keywords = "PH, Soil water repellency, Surface charge",
author = "D. Diehl and Bayer, {J. V.} and Woche, {S. K.} and R. Bryant and Doerr, {S. H.} and Schaumann, {G. E.}",
note = "Copyright: Copyright 2010 Elsevier B.V., All rights reserved.",
year = "2010",
month = sep,
doi = "10.1016/j.geoderma.2010.06.005",
language = "English",
volume = "158",
pages = "375--384",
journal = "GEODERMA",
issn = "0016-7061",
publisher = "Elsevier",
number = "3-4",
}