Persistence of water repellency in coarse-textured soils under various types of forests in NW Spain

The primary purpose of this work was to assess the persistence of water repellency in the surface horizon of coarse-textured soils under natural Quercus robur ecosystems, and Pinus pinaster and Eucalyptus globulus plantations, in the northwest of the Iberian Peninsula. Water repellency was determined by applying the water drop penetration test (WDPT) to soil samples collected from variable depths (0–40 cm). Measurements were made on field-moist samples obtained at the end of the dry period and on samples dried at 25ºC in the air. All soils exhibited very high (severe to extreme) water repellency in the topmost soil layer (0–5 cm) but no significant differences among the three plant species studied. Extreme persistence was observed down to 20 cm in the soils under eucalyptus and down to 10 cm in those under pine. The soils under oak were those exhibiting the highest variability in water repellency and the greatest decrease in it with increasing depth (especially in relation to soils under eucalyptus).

Water repellency exhibited significant positive correlation with the C content and C/N ratio of the soils. Soil water repellency was similar in the air-dried samples and field-moist samples.