Water repellency of soils; the influence of ambient relative humidity

Adverse effects of soil water repellency (hydrophobicity) are of concern during or following rainfall or irrigation, and are often preceded by conditions of high atmospheric relative humidity (RH). Assessments of repellency are, however, commonly conducted on air-dried samples at ambient laboratory conditions. This study explores the effects of differing antecedent RHs (32-98%) on the water repellency of air-dried soils of wide ranging characteristics under laboratory conditions using water drop penetration time (WDPT) and ethanol-percentage tests. Most samples exhibited considerably higher water repellency after exposure (< 1 d) to 98% RH compared with lower RHs, typical of ambient laboratory conditions. This work suggests that previous studies mayhave incorrectly classified some soils, likely to exhibit water repellency in the field, as wettable, and that tests carried out following exposure of samples to high RH provide assessments that best reflect critical field conditions.