Increase in Hydrophobicity of Andisol Under Soil Surface Heating.

Soil is often exhibit hydrophobic properties after a forest fire. Experiments conducted by DeBano et al. (1976) showed that the organic compounds in the soil become volatized under high-temperature, moving downward along with the soil temperature gradient, and forming a hydrophobic layer at some depth within the soil profile where soil temperature is rather low. However, neither of these studies considered the important effects of oxygen on the morphological changes of organic matter in soil.  In this study, we aimed to clarify the changes in soil hydrophobicity as well as soil organic matter content in response to heating of the ground surface at the field and laboratory experiment.  Forest Andisol had high soil organic matter content used in this study.  Near surface soil temperature rose to 600 and 700 Celsius degree under soil surface heating at laboratory and field experiment, respectively. In the laboratory muffle furnace experiment, soil samples heated under oxygen-deficient ambience exhibited similar carbon and nitrogen dynamics and hydrophobicity with the soil suffered similar temperatures at the field experiment.  Both, field and laboratory experiment showed that soil at certain depth from the surface where the soil could be under anoxic condition during surface burning exhibited distinct hydrophobicity while a skin of the soil surface had almost no hydrophobicity after burning.  This indicated that the soil might be anoxic when the ground surface is burned and this would cause soil hydrophobicity.  Consequently, under conditions of ground-surface heating, the presence or absence of oxygen in soil air-phase appears to have a marked effect on develop in soil hydrophobicity.