Heating affects properties of forest soils with different texture: 1. Physical and chemical properties

Wildland fires affect physical and chemical properties of forest soils, and the magnitude of their effects depends on the soil temperature achieved during a fire. Laboratory heating of soil samples in muffle furnace was used to simulate a natural fire heating of forest soils, although it does not completely reproduce natural fire conditions. The effect of heating temperature of 100–900°C on particle size distribution, soil water repellency (SWR), soil organic carbon content (SOC) and pH was estimated in three soils differing in texture (sandy soil, silty-clay soil, and clay soil) sampled in coniferous and deciduous forests at Gbely (Areni-Gleyic Umbrisol), Hviezdoslavov (Fluvisol) and Gabčíkovo (Fluvisol), respectively. Decrease in the clay content and increase in the sand content was large in silty-clay and clay soils, but not as large in sandy soils. Surprisingly, heating the soil to 100°C, commonly used in soil moisture measurement, caused a decrease in clay content by half (the average value for all soils). This finding should be confirmed by further measurements on the soils from other regions, because the degree of aggregation depends also on the type of clay and other minerals. The persistence of SWR gradually increased in the heating temperature range 100–300°C in all three soils from coniferous forests and sandy soil from deciduous forest, and was absent in the remaining two soils. The SOC decreased and pH increased with increasing heating temperature.