Spectral characteristics of water-soluble and alkaline-soluble organic substance of fallow light-gray forest soils

The content of organic matter (OM) and its individual fractions were studied in different ages (7 and 75-80 years-old) fallow soils. The qualitative composition of labile OM fractions was evaluated by the criteria of SUVA254 and Sr, which were calculated from the absorption spectra in the UV range. It was shown that as deposits age, there is a significant increase in the content of total organic carbon (TOC) in soils and a change in the qualitative composition of its labile fractions. From the nature of changes in the degree of aromaticity and molecular masses of labile fractions with the age of deposits, a conclusion can be drawn that the factor of selective preservation of compounds resistant to degradation is relevant only to stabilize the water-soluble OM. The stability of alkaline-soluble OM fractions is most likely provided by the formation of organic and organic-mineral associations.