Comparing capillary rise contact angles of soil aggregates and homogenized soil

Juan C. Ramirez-Flores, Susanne K. Woche, Joerg Bachmann*, Marc-O Goebel, Paul D. Hallett

*Corresponding author for this work

Research output: Contribution to journalArticle

24 Citations (Scopus)

Abstract

Soil wettability affects physical properties such as aggregate stability, infiltration rate, or erodibility. To describe the wetting properties of soil, the soil–air–water contact angle (CA) is often used. At present, a direct measurement of the CA determined on intact soil aggregates and a direct comparison with corresponding homogenized aggregates is still lacking, mainly because standard methods have not been defined to measure the wettability of soil aggregates. In this study, the Capillary Rise Method (CRM) was used to assess contact angles of single intact 1–2 mm soil aggregates, packings of intact aggregates and packings of crushed (homogenized) aggregates of 9 topsoils and 3 humus subsoils from 5 sites in Germany. In general, CAs of the homogenized aggregates were quite similar for all soils (65° ± 10°), while CAs for aggregate packings and single aggregates generally were larger for grassland and forest soils (60° to 80°) than for arable soils (0° to 20°). It was concluded that all soils contain potentially hydrophobic pore surfaces, but the effectiveness of these surfaces to create water repellency depends on the small-scale architecture of the pore space and the distribution/position of hydrophobic components inside the matrix. These findings suggest that it is misleading, particularly for agricultural soils, to quantify wetting properties by only analyzing homogenized soil. We propose that CRM-CA measurements should be extended to investigations of intact aggregates and the wetting coefficient k = cosθ should also be displayed to distinguish more clearly between completely wettable soils and soils with low subcritical repellency. Finally, it should be noted that the methods proposed are only applicable to non-hydrophobic soil exhibiting subcritical water repellency (CA > 0°,…, CA ≤ 90°).

Original languageEnglish
Pages (from-to)336-343
Number of pages8
JournalGeoderma
Volume146
Issue number1-2
Early online date21 Jul 2008
DOIs
Publication statusPublished - 31 Jul 2008

Keywords

  • grassland
  • management
  • penetration
  • organic-matter
  • forest
  • dynamics
  • soil aggregates
  • arable land
  • contact angle
  • porous-media
  • surface
  • physical protection
  • wettability
  • size
  • Capillary Rise Method

Cite this

Comparing capillary rise contact angles of soil aggregates and homogenized soil. / Ramirez-Flores, Juan C.; Woche, Susanne K.; Bachmann, Joerg; Goebel, Marc-O; Hallett, Paul D.

In: Geoderma, Vol. 146, No. 1-2, 31.07.2008, p. 336-343.

Research output: Contribution to journalArticle

Ramirez-Flores, JC, Woche, SK, Bachmann, J, Goebel, M-O & Hallett, PD 2008, 'Comparing capillary rise contact angles of soil aggregates and homogenized soil', Geoderma, vol. 146, no. 1-2, pp. 336-343. https://doi.org/10.1016/j.geoderma.2008.05.032
Ramirez-Flores, Juan C. ; Woche, Susanne K. ; Bachmann, Joerg ; Goebel, Marc-O ; Hallett, Paul D. / Comparing capillary rise contact angles of soil aggregates and homogenized soil. In: Geoderma. 2008 ; Vol. 146, No. 1-2. pp. 336-343.
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AU - Woche, Susanne K.

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AU - Hallett, Paul D.

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AB - Soil wettability affects physical properties such as aggregate stability, infiltration rate, or erodibility. To describe the wetting properties of soil, the soil–air–water contact angle (CA) is often used. At present, a direct measurement of the CA determined on intact soil aggregates and a direct comparison with corresponding homogenized aggregates is still lacking, mainly because standard methods have not been defined to measure the wettability of soil aggregates. In this study, the Capillary Rise Method (CRM) was used to assess contact angles of single intact 1–2 mm soil aggregates, packings of intact aggregates and packings of crushed (homogenized) aggregates of 9 topsoils and 3 humus subsoils from 5 sites in Germany. In general, CAs of the homogenized aggregates were quite similar for all soils (65° ± 10°), while CAs for aggregate packings and single aggregates generally were larger for grassland and forest soils (60° to 80°) than for arable soils (0° to 20°). It was concluded that all soils contain potentially hydrophobic pore surfaces, but the effectiveness of these surfaces to create water repellency depends on the small-scale architecture of the pore space and the distribution/position of hydrophobic components inside the matrix. These findings suggest that it is misleading, particularly for agricultural soils, to quantify wetting properties by only analyzing homogenized soil. We propose that CRM-CA measurements should be extended to investigations of intact aggregates and the wetting coefficient k = cosθ should also be displayed to distinguish more clearly between completely wettable soils and soils with low subcritical repellency. Finally, it should be noted that the methods proposed are only applicable to non-hydrophobic soil exhibiting subcritical water repellency (CA > 0°,…, CA ≤ 90°).

KW - grassland

KW - management

KW - penetration

KW - organic-matter

KW - forest

KW - dynamics

KW - soil aggregates

KW - arable land

KW - contact angle

KW - porous-media

KW - surface

KW - physical protection

KW - wettability

KW - size

KW - Capillary Rise Method

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DO - 10.1016/j.geoderma.2008.05.032

M3 - Article

VL - 146

SP - 336

EP - 343

JO - Geoderma

JF - Geoderma

SN - 0016-7061

IS - 1-2

ER -