Temporal fluctuations of water repellency in forest soils of Galicia, NW Spain. Do soil samples dried at laboratory reflect the potential soil water repellency?

Abstract

AbstractWater repellency is a widespread property of Pinus pinaster and Eucalyptus globulus forest soils in NW Spain and is particularly severe during the summer dry conditions. The aim of this work was to compare actual water repellency at field‐moist samples with potential water repellency after drying at 25 and 105 °C in samples collected at different times of year under four forest soils. Also, we investigated whether drying at 25 or 105 °C led to repellency values comparable to the highest levels reached under field conditions in the summer with a view to developing an appropriate sampling protocol towards estimating the maximum possible water repellency of a given soil as a key to establishing its environmental effects. The actual and potential water repellency was determined by using the water drop penetration time (WDPT) and molarity of an ethanol drop (MED) tests.Clear seasonal patterns of water repellency were observed from the results for the four forest soils, peaking in the dry period and disappearing after prolonged wet periods. Water repellency lasts longer in sandy loam soils than in more finely textured soils, and also under eucalyptus than under pine forests. Drying soil samples at 25 or 105 °C increased water repellency, as measured with the WDPT method, in the four soils, but especially in the non‐repellent samples collected during the wet period. The increase was more marked in the sandy loam soils than in the more finely textured soils, and also after drying at 105 °C than at 25 °C. MED measurements exposed a common trait in the four soils; thus, the water repellency values obtained under field conditions in summer invariably exceeded those obtained after drying at 25 or 105 °C. In addition, the repellency values for dried samples collected in the wet period were never comparable to the maximum levels observed under field conditions in the summer. Copyright © 2011 John Wiley & Sons, Ltd.