RELATIONSHIP BETWEEN SOIL COLOR AND TEMPERATURE IN THE SURFACE HORIZON OF MEDITERRANEAN SOILS: A LABORATORY STUDY.

Changes in color parameters with increasing temperatures over the range of 20 to 700 [degrees]C were studied in samples from the uppermost surface layer of the A horizon of various typical Mediterranean soils. Because changes in soil color during heating relate to the formation of Fe hydrous oxides species (such as maghemite and hematite) that increase the red color, and the close relationship between the redness rating index (RR) (a color index that is easily measurable) and hematite content, we studied the potential relationship between such an index and the temperature reached by soil samples over the range of 20 to 700 [degrees]C. The variation of the RR index with temperature was found to be similar in large soil groups. This allows the estimation of the temperature reached by a soil sample from the increase in redness rating index, provided the variation of RR with temperature for the soil group concerned has previously been determined. This study provides a first approximation to the estimation of the temperature level reached by the soil during a fire and the soil damage by effect of vegetation burning, which depends on the temperature reached. The soil temperature increase by fire is short-lived, but the changes induced in the color and other soil properties by fire are more or less permanent.