Water repellency under different plant species in a calcareous forest soil in a semiarid Mediterranean environment

Water repellency (WR) is a property that has implications on the hydrologic balance in affected soils. In semi-arid areas where water supply is limited, even slight WR may play an important role in the infiltration and spatial distribution of precipitation into the soil. Acidic and sandy-textured soils have been demonstrated to be more prone to develop WR, but there are studies reporting water repellent properties in other soil types. In the present study we investigated soil WR under four plant species in a semi-arid area with a calcareous, medium-textured forest soil. For this purpose, 160 soil samples were taken at micro-sites under different species (Pinus halepensis, Quercus coccifera, Juniperus oxycedrus and Rosmarmus officinalis). Soil WR was measured with the water drop penetration time (WDPT) test on air-dried samples. Samples with WDPT > 5 s were classified as water repellent. WR was present in 20% of the samples, and its persistence ranged mainly between 10 and 30 s. Under P. halepensis and Q. coccifera, WR occurred more frequently (40 and 30%, respectively) than under J. oxycedrus and R. officinalis (only 5% in both cases). In order to know the causes of the difference in occurrence of WR under the selected species and to establish relationships, soil organic matter (SOM) content and pH were measured for a selection of 66 samples, including all 32 water repellent and 34 wettable samples selected from those taken under the four species (n = 66). A negative relationship between WR and pH was found for all species. Moreover, in the case of P. halepensis soil samples, a positive correlation between WR and SOM content was found. A discriminant analysis allowed for the distinction between water repellent and wettable conditions in calcareous soils, based on the information provided by pH, SOM content and vegetation type. Soil pH turned out to be the most important parameter for discrimination. The hydrological and ecological implications from these results are discussed with special focus on the areas in the region extensively afforested with P. halepensis. Copyright (c) 2007 John Wiley & Sons, Ltd.