Vapour and liquid hydrophobic characteristics induced by presence of surfactants in an agricultural soil

Surfactants affect the water-related soil properties of water-repellent soils but may also affect those of wettable soils. The effect of five surfactants, belonging to three different types, at different concentrations on the hydrophobic behaviour of a nonrepellent agricultural calcareous soil is studied. Native soil was treated with anionic (Aerosol 22), cationic (TDTMA and HDTMA) and non-ionic surfactants (Triton X-100 and Tween 80) and vapour and liquid hydrophobic characteristics were evaluated. Anionic and non-ionic surfactants at any concentration increase water vapour adsorption but cationic ones reduce it when applied to soil above 50% soil cation exchange capacity. Absorption of liquid water is restricted for all soil treatments with proven changes in water penetration time and wetting contact angles. Surfactant interactions with the soil matrix are related with changes in organic carbon and cation exchange capacity of the soil. Derived apparent contact angles from an imbibition test provide a suitable discrimination of soil wettability using a simple and efficient method for a large number of trials using small soil samples.