EFFECT OF LAND USE AND SOIL PROPERTIES ON SOIL TEMPERATURE DISTRIBUTION OF CAMBISOLS IN MOUNTAIN REGIONS
The aim of this study was to assess the effect of land use, location, and soil properties on the distribution and dynamics of the soil temperature, the accumulated heat and the apparent thermal diffusivity of Cambisols in three mountain regions in Bulgaria. Annual distribution of the soil temperature (Ts) of Cambisols was registered under different land use (grassland, bare soil, deciduous and coniferous vegetation) during period June 2018-May 2021. Every day measurements were realized at 0, 2, 5, 10, 20, and 50 cm depths in 11 plots within the territory of the experimental stations Gabra (~920 m.), Govedartzi (~1540 m.), and Igralishte (~850 m) of the Forest Research Institute, situated in the Lozen, Rila and Maleshevska Mountains, respectively, in the South-Western part of Bulgaria. The experimental stations differ in climatic conditions and soil physical and chemical properties. The heat accumulated in 0-50 cm soil layer was assessed by the sum of Ts for the period with Ts > 5oC. The heat accumulated in bare soil was the highest (4067-3544oC), followed by the sums under grassland (3849-3453 oC) and forest (3096-3300 oC) in Gabra and Igralishte. The relative decrease of the accumulated heat under woodland in comparison to grassland was 18-20% in Gabra and 4-7% in Igralishte. At the higher elevation in Govedartzi the heat accumulated under grassland was 10-12% less than under woodland. The apparent thermal diffusivities () were estimated using annual amplitudes of Ts at depths
0.02 and 0.20 m. The data showed that the values of under grass in Gabra 0.212 mm2 s-1 and in Igralishte 0.535 mm2 s-1 were higher than under forest vegetation 0.061-0.133 mm2 s-1 and bare soil 0.049-0.071 mm2 s-1. In Govedartzi the thermal diffusivity was higher 0.118 mm2 s-1 under Norway spruce than under grassland 0.070 mm2 s-1 and Scots pine 0.079 mm2 s-1.
Keywords: Soil temperature distribution, Cambisols, Mountains, Land use, Bulgaria.