Viscosimetric and chromatographic studies of soil humic acids

Abstract

The aim of this study was to obtain information on molecular parameters of humic acids (HA) extracted from soils under various fertilization treatments. HAs were extracted from a grey-brown podzolic soil and chernozem under two long-term static field experiments. The fertilization variants were control (without fertilization) and manuring. Viscosimetric and gel permeation chromatography determinations were conducted in NaOH (pH = 10.5) and NaCl (pH = 7.0) solutions. A few models were used for calculations of the shapes of the HA molecules. The results confirmed the properties of HAs typical for high-molecular polyelectrolytes. The size of their molecules depended on the pH and the concentration of HAs in solution. As pH increased, both their mean molecular weight and spheric parameters increased. Fertilization modified molecular parameters of HAs. HAs extracted from the soils under mineral fertilization had molecules of similar parameters. HAs from manured soils had lower mean molecular weight associated with a supply of fresh organic matter.