In the past, hydrophobic soils have been associated mostly with preferential flow phenomena. It has become increasingly evident that besides the phenomena of extremely (hydrophobic) water‐repellent soils, soils with reduced wettability are more the rule than the exception. Despite the extensive literature on the hydraulic behavior of water‐repellent soil, a conceptual model flexible enough to describe typical behavior of wettable and hydrophobic soils as well as for soils with intermediate wetting properties is still missing. We propose a water‐content and time‐dependent contact angle (CA) model that was used as an extension of the van Genuchten equation for the capillary pressure–saturation (CPS) relationship. This model is based on conventional retention parameterizations; that is, the hydrophilic soil is considered as a special case of the general wetting model. Hydrophobic soils as well as soils with subcritical (reduced wettability, not hydrophobic) water repellency are represented by this model. Conceptually, the proposed model links microscopic interfacial properties, indicated by the CA, with the macroscopic hydraulic model mainly by modifying the α of the van Genuchten equation. The modification basically accounts for hysteresis of the main drainage–main wetting branch of the CPS relationship. Compared with conventional hydraulic models, only a few more parameters are needed to describe the wettability extension of the model: mean maximum and minimum CAs and their autocorrelation functions. Additionally, characteristic rewetting time and a breakthrough pressure function are needed for a complete description of the hydraulic properties of the soil. This extended hydraulic model serves as a base for a simulation study in unsaturated soil with reduced wettability.

The shortage of fresh water (FW) in Israel and other semiarid regions has forced farmers to significantly expand the use of treated wastewater (TWW). Recently, farmers utilizing reclaimed wastewater (TWW) reported a unique type of water distribution regime in drip-irrigated soils, as follows: (i) limited wetted area on the soil surface; and (ii) small saturated areas around and below the dripper, in TWW irrigated soil as opposed to an even, onion-like wet profile, formed under fresh water (FW) irrigation. Following this observation in the field and after conducting preliminary tests in the laboratory, we hypothesized that TWW irrigation introduces water-repellent organic constituents into the soil. Tests characterizing the water distribution showed the diameter of the saturated area on the soil surface and its water content (at a depth of 0-10 cm) was smaller with TWW than with FW irrigation. The TWW accumulated on the soil surface in small lenses and then flowed rapidly into the ground. The repellency of soils irrigated with FW and TWW was measured with the water drop penetration time test. Soils irrigated with FW were hydrophilic, whereas those irrigated with TWW exhibited hydrophobicity. Fourier transform infra-red spectroscopy (FTIR) and 13 C-NMR analyses of organic components extracted from the soils with organic solvents indicated differences in composition only at a depth of 0-2 cm. Extracting soils with a methanol þ chloroform (1:1, by volume) mixture was found to be very effective in the removal and extraction of hydrophobic aliphatic components from soils irrigated with TWW.

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