Sieving effect on the intensity and persistence of water repellency at different soil depths and soil types from NE-Spain

Soil water repellency has been studied for different soil types and plant covers, but uncertainty exists regarding the representativeness of water repellency measured on unaltered soil surfaces compared to sieved samples. Two different methods are used to characterize water repellency, which provide a certain degree of different information: the persistence of soil water repellency, measured by the water drop penetration time (WDPT) test; and the intensity of soil water repellency, measured by the ethanol percentage (EP) test. The main objectives of this research were to analyze the relationships between soil water repellency measured on undisturbed soil blocks and 2-mm hand sieved samples, and to compare the results between both methods (WDPT and EP tests). Water repellency was measured on the surface and at soil depths of 2 cm and 5 cm for three fine textured soil types (Rendzic Phaeozem, Hypercalcic Calcisol, and Eutric Cambisol) developed below different plant covers (mossy pine forest, evergreen oak forest, and meadow, respectively).At the class level, WDPT and EP tests offered similar results for unaltered and sieved samples. The EP test tends to slightly overestimate values on sieved samples, whereas the WDPT test tends to slightly underestimate measurements on sieved samples. Based on the good relationship between the two types of soil samples used (unaltered and sieved), conversion formulas for both tests have been obtained: a linear regression for EP test (R2 = 0.862; p < 0.001) and a logarithmic model for WDPT test (R2 = 0.913; p < 0.001).Differences in the wettability has been observed between soil depths and soil types: Rendzic Phaeozem under pinewood is very strongly hydrophobic and consistently severely water repellent at any soil depth; Hypercalcic Calcisol under oakwood has the same behavior on the surface, but water repellency decreases progressively with depth; finally, Eutric Cambisol under meadows is hydrophilic and mainly wettable for all depths.