Influence of heating on various properties of six Mediterranean soils. A laboratory study

The influence of temperature between 25–500 °C on several physical and chemical properties was studied on samples collected from six typical Mediterranean soils. In all soil samples, an increase in the temperature of the soil heating was found to decrease organic matter content. Soil color was affected in several ways. In soil samples having high organic matter content, the Brightness values decreased in the 25–200 °C interval and increased between 200–500 °C. In contrast, the Chroma values increased mainly between 200 to 500 °C. The RR redness index values also increased between 200 and 500 °C because of the higher Chroma and the redder Hue. The pH decreased except in the samples from the high organic surface horizons where the pH increased at temperatures above 300 °C. The soil sample containing low amount of organic matter, but rich in clay and carbonates, showed similar changes; in this case, the decomposition of magnesium carbonate also was believed responsible for the increase in soil pH at temperatures greater than 300 °C. Soil texture changes associated with increasing temperature included an increase in sand and a decrease in clay content. Increasing soil temperatures up to 500 °C drastically reduced the amount of water-stable aggregates but at the same time increased the sand content. The electric conductivity increased with temperature in the 100 to 300 °C interval and decreased at 500 °C.