Effects of heating and post-heating equilibration times on soil water repellency

The effects of variation in heating temperature T ( 50 - 300 degrees C), heating duration ( 20 - 60 min), and post-heating equilibration times ( 24 - 168 h at 20 degrees C and 50% relative humidity) on the wettability, as measured by the Critical Surface Tension (CST) method, of 4 initially water repellent soils from Canada, Portugal, and the UK are reported. All soils show an increase in water repellency following heating at temperatures in the range of 50 to 150 degrees C, followed by a considerable decline after heating to 200 - 250 degrees C, and, except for one soil, the eradication of repellency after heating to 300 degrees C. For two soils with a comparatively high organic carbon content and. ne texture, water repellency levels were also affected by the length of the post-heating equilibration period. The results demonstrate that (i) the common practice of heating samples to 105 degrees C does not provide a viable standard procedure for the measurement of water repellency as it may alter repellency to different degrees, and (ii) where heat treatment is required, a post-heating equilibration time of 24 h is not necessarily sufficient for sample repellency levels to adjust to atmospheric laboratory conditions; therefore it is advisable to prolong equilibration to at least one week prior to measurement.