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. (paper)