TY - JOUR

T1 - Comparing capillary rise contact angles of soil aggregates and homogenized soil

AU - Ramírez-Flores, Juan C.

AU - Woche, Susanne K.

AU - Bachmann, Jörg

AU - Goebel, Marc O.

AU - Hallett, Paul D.

N1 - Funding Information: The results of this paper are part of the research project “Surface Energy Characterization of Heterogeneous Porous Media: Theoretical and Experimental Assessment of the Wettability of Soil” financed by the Niedersachsen Foundation (NHDF No. 22002) and was partly supported by the priority program of the German Research Foundation DFG (SPP 1090). We also like to thank the “Höhere Landbauschule Rotthalmünster” for the possibility to take soil samples from their long-term experimental site and Axel Lamparter for his help during the sampling campaign. The Scottish Crop Research Institute receives grant-in-aid from the Scottish Government Rural and Environment Research and Analysis Directorate. Copyright: Copyright 2008 Elsevier B.V., All rights reserved.

PY - 2008/7/31

Y1 - 2008/7/31

N2 - 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°).

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 - Arable land

KW - Capillary Rise Method

KW - Contact angle

KW - Forest

KW - Grassland

KW - Soil aggregates

KW - Wettability

UR - http://www.scopus.com/inward/record.url?scp=48349139680&partnerID=8YFLogxK

U2 - 10.1016/j.geoderma.2008.05.032

DO - 10.1016/j.geoderma.2008.05.032

M3 - Article

AN - SCOPUS:48349139680

VL - 146

SP - 336

EP - 343

JO - GEODERMA

JF - GEODERMA

SN - 0016-7061

IS - 1-2

ER -