The yield values of densimetric fractions from typical chernozems of different land use types

One of the most justified and applied approaches to isolating pools of soil organic matter is fractionation in heavy liquids. The main problem with this approach is rather large losses in the separation of fractions at the stage of washing fractions from heavy liquids. The paper presents a densimetric fractionation protocol that can significantly reduce these losses. It is suggested to use 0.001 M HCl for washing. This approach, in comparison with distilled water, allows reducing losses of weight from 15 to 5% and of carbon from 7.5 to 2.5%. The paper provides a detailed protocol, used by the Laboratory of Soil Biochemistry of V.V. Dokuchaev Soil Science Institute, to isolate four densimetric fractions using sodium polytungstate solutions: free and occluded SOM with a density of 2.0 g/cm3. In the work we used samples of typical chernozems of different land use types. It was shown that the processes of soil restoration and degradation significantly affect the content of light occluded soil organic matter.