Modified sessile drop method for assessing initial soil–water contact angle of sandy soil

Existing methods for determining the soil–water contact angle as a measure of water repellency are either indirect, cumbersome, or time‐consuming. Our objective was to develop a method that is simpler than existing procedures and that still yields accurate results. The proposed method represents a modified sessile drop method for measuring the initial contact angle of powdered or granular material. The measurements are made by placing a layer of uniform soil particles onto adhesive tape, adding droplets of deionized water, and reading off the contact angle at the three‐phase boundary line with a goniometer‐fitted microscope immediately after placing the drops on the soil sample. Sieved soil fractions <63 μm, 63 to 100 μm, and 100 to 200 μm were used to ensure particle layer uniformity. The method was tested on 10 samples from different depths of a sandy soil profile. The contact angles measured on these soil fractions were compared with the water drop penetration time (WDPT) test and the capillary‐rise method. The contact angles of the fractions <63 μm and 63 to 100 μm compared reasonably well with those measured with the capillary‐rise method and their rank order agreed in general with that of the WDPT test. We conclude that the new method appears to be promising for the simple, rapid, and reproducible determination of the contact angle of sandy soils. The sessile drop method can be used in a wider range of water repellency conditions compared with either the capillary‐rise or the WDPT method.