A Study of Soil Organic Matter Stability Using Derivatography and Long-Term Incubation Methods

Soil organic matter (SOM) includes many classes of labile compounds available for microbial decomposition or, conversely, stable compounds protected from biodegradation by biological, chemical, and physical stabilization. It is believed that the more thermal energy is spent on the destruction of soil organic matter, the more stable and more resistant for biodegradation it is. We compared the thermal and biological stabilities of organic matter in eleven soil types from deciduous forest, forest-steppe, steppe, and semidesert bioclimatic areas of the European Russia. According to the activation energy (Ea), the highest SOM thermal stability was typical of the ordinary chernozem and meadow vertic soil. The lowest SOM thermal stability was found for gray forest soil; other soil types were characterized by an intermediate resistance towards thermal oxidation. The thermally labile pool ( 390–400°C) was on the average 59% (40–68%). The SOM biological stability estimated by the ratio of potentially mineralizable organic matter to that resistant to mineralization (biological stability index) decreased in the following order: ordinary chernozem (Haplic Chernozem (Loamic, Pachic)) > meadow vertic soil (Pellic Vertisol (Gleyic, Humic)) > gray forest soil (Luvic Greyzemic Phaeozem (Loamic)) = meadow chestnut soil (Gleyic Kastanozem (Chromic)) > meadow solonetz (Endosalic Gleyic Solonetz (Loamic, Cutanic)) > alluvial meadow soil (Eutric Fluvisol (Humic, Oxyaquic)). The potentially mineralizable SOM pool in the studied soils was 6–27-fold lower as compared with the pool of thermally labile SOM, and the parameters that characterize SOM thermal stability did not correlate with the biological stability index. Thus, SOM thermal lability is not identical to its biodegradability.