MODIFICATIONS INDUCED IN SOIL PHYSICOCHEMICAL PARAMETERS BY EXPERIMENTAL FIRES AT DIFFERENT INTENSITIES

Field studies on the effects of heating soil are rare, Studies in whic h the temperature was varied and measured are even rarer, To cover thi s lack of knowledge, we conducted some experimental fires in which the fuel was controlled to obtain different fire intensities, Induced tem peratures were measured by k-type thermocouples placed at various soil depths, These induced temperatures were highly variable at the soil s urface, whereas below 2.5-cm depth, the temperature rise was negligibl e. Modifications of various soil physico-chemical parameters caused by fire were related to increasing temperatures at the soil surface, The passage of fire promoted the aggregation of clay particles into sand- sized particles, which become even more resistant to the disrupting ac tion of water, The soil pH decreased at temperatures up to 395 degrees C, followed by a clear increase at higher temperatures; however, both the cation exchange capacity and the organic matter content decreased continuously with increasing soil temperature, Total nitrogen content remained surprisingly constant as the soil surface temperature increa sed, whereas ammonium nitrogen peaked at 184 degrees C. The organic ph osphorus decreased continuously, and the available fractions increased . These results are in agreement with the results of our previous rese arch on the effects of the artificial heating on soil properties and c onfirm that the processes occurring in soil are related to the tempera ture reached during the fire, The ashes, at least immediately after fi re, do not affect these processes.