Abstract. This study undertook to map the composition and stock of organic matter in soils formed on bedrock types differing in resistance to weathering and mineralogical composition. Studies of the specific features of organic matter transformation in soils formed over bedrock have demonstrated differences depending on the parent rock characteristics. The influencing factors include the chemical composition of the rock and its weatherability. Where rocks have a rich composition – basic and ultrabasic – but are deeply metamorphosed (and, hence, resistant to weathering), there forms primitive soils with a low content of organic matter, which is mostly confined to the top organic horizon. Besides, organic matter in such soils is of fulvic nature, which is generally typical of the zonal soils. Primitive soils are not very fertile, both due to the relatively low content of organic matter and to the limited availability of mineral nutrients for plants. The fertility of shallow soils on acid parent rocks is limited by high acidity and a low content of mineral nutrients both in the parent rock eluvium and in the soil’s native mineral material. The productivity of soils on basic rocks is somewhat higher. The conditions for the biota are the most favorable in shallow soils forming on carbonate rocks. They contain substantial amounts of nutrients and have comparatively low weatherability, which makes these resources available. In the organic matter of these soils, humic acids prevail over fulvic acids, even if slightly. Organic matter stores in such soils are distributed more evenly, with a substantial share concentrated in mineral horizons, in the root layer.
Keywords: soil, organic matter, parent rock