Relationship between specific surface area and the dry end of the water retention curve for soils with varying clay and organic carbon contents

Abstract

Accurate description of the soil water retention curve (SWRC) at low water contents is important for simulating water dynamics and biochemical vadose zone processes in arid environments. Soil water retention data corresponding to matric potentials of less than −10 MPa, where adsorptive forces dominate over capillary forces, have also been used to estimate soil specific surface area (SA). In the present study, the dry end of the SWRC was measured with a chilled‐mirror dew point psychrometer for 41 Danish soils covering a wide range of clay (CL) and organic carbon (OC) contents. The 41 soils were classified into four groups on the basis of the Dexter number (n = CL/OC), and the Tuller‐Or (TO) general scaling model describing water film thickness at a given matric potential (<−10 MPa) was evaluated. The SA estimated from the dry end of the SWRC (SA_SWRC) was in good agreement with the SA measured with ethylene glycol monoethyl ether (SA_EGME) only for organic soils with n > 10. A strong correlation between the ratio of the two surface area estimates and the Dexter number was observed and applied as an additional scaling function in the TO model to rescale the soil water retention curve at low water contents. However, the TO model still overestimated water film thickness at potentials approaching ovendry condition (about −800 MPa). The semi–log linear Campbell‐Shiozawa‐Rossi‐Nimmo (CSRN) model showed better fits for all investigated soils from −10 to −800 MPa and yielded high correlations with CL and SA. It is therefore recommended to apply the empirical CSRN model for predicting the dry part of the water retention curve (−10 to −800 MPa) from measured soil texture or surface area. Further research should aim to modify the more physically based TO model to obtain better descriptions of the SWRC in the very dry range (−300 to −800 MPa).

Estimation of Soil Clay Content from Hygroscopic Water Content Measurements

“…Th erefore, we hypothesize that soil hygroscopic water content, whose determination is fast and technically less involved than particle-size analysis, positively correlates with clay percentage in both temperate and tropical soils and can provide a useful surrogate for soil clay content. Other research groups have presented results that emphasize the strong correlation between hygroscopic water and clay contents (Banin and Amiel, 1970;Petersen et al, 1996;Tuller and Or, 2005;Resurreccion et al, 2011); however, there is no specifi c water potential or relative humidity (RH) agreed on at which these relationships should be determined.…”

A new theoretical model accounting for film flow in unsaturated porous media

“…[17] Although the Langmuir model was derived for low ionic strength solutions, the exponential form between film thickness f REV (or water content ) and matric potential h REV (4/ << h REV at low water contents) of different soils were proved to be reliable not only in other SWRC models that account for film flow (e.g., the (h) model introduced by Tuller and Or [2005]), but also in laboratory experiments (e.g., the measured h(f) of different soils at very dry ranges in Resurreccion et al [2011]). …”

“…The details of our experiment were the same as those of Resurreccion et al [2011]. First, air-dried samples of 10 g were prepared and a small amount of water was added.…”

Predicting the soil water characteristic curve from the particle size distribution based on a pore space geometry containing slit-shaped spaces

“…Previous work showed that the S SA of soil is closely dependent upon the soil texture and that it could be estimated from the 5 soil media data and PSD (Sepaskhah and Tafteh, 2013;Resurreccion et al, 2015). The method used to estimate the S SA in Sect.…”