The new approach to assessing the qualitative composition of soil organic matter

Abstract

There is an opinion [1] that both humic substances (HSs) and non-humic ones pass into alkaline extract from soil organic matter (SOM). Therefore, it became necessary to develop new approaches for isolation of HSs. In this publication, the motivation for new approaches for isolation of HSs, including melanins, from soil organic matter was provided based on a review of the scientific literature. These approaches include: (i) isolation of individual organic compounds, which are soluble in 90% dimethyl ketone (acetone) solution (specifically chlorins and carotenoids); (ii) isolation of HSs plus melanins and glomalins in 90% dimethyl ketone solution with HCl; (iii) sorption of HSs plus melanins and glomalins by a sorbent (in particular based on capronic acid); (iv) desorption of glomalins by phosphate buffer solutions with pH = 7; (v) desorption of HSs including melanins by phosphate buffer solutions with pH = 9, and 11, and 0.1 M NaOH solution with pH = 13. According to the existing classification, isolated HSs including melanins can be categorized as humic acids, but no fulvic acids have been found.