Acid–base properties of water-soluble organic matter of forest soils, studied by the pK-spectroscopy method

Using the potentiometric titration and pK spectroscopy method, acid–base properties of water-soluble organic matter of forest soils have been studied. Five acidic classes composed of different substances with pKa values around 3.6; 4.8; 6.7; 8.7 and 9.7 have been identified. Testing the properties of soluble soil fraction, it is to be taken into account that when it is isolated from non-soluble soil matter, some water-soluble substances remain in soil and do not pass into the solution. Most firmly adsorbed in soil are water-soluble components with pKa 9.6–9.8.