NEGATIVE CHARGE PH-DEPENDENCE OF ORGANIC-MATTER OF FOREST SOIL UNDER INFLUENCE OF LIMING AS DETERMINED FROM TITRATION CURVES

The dependences between negative charge and pH for organic matter of l imed and unlimed profiles of sandy acidic forest soils were determined on the base of ion exchange and titration curves measurements. Subtra cting the titration curves of the supernatant from the titration curve s of the respective suspensions the quantities of base consumed by sol id phases were determined. They were interpreted in terms of negative charge after corrections with the quantities of initial exchangeable b asic cations and exchangeable hydrogen. For investigated organic mater ial the charge increased slowly in acidic pH region and much faster in alkaline pH region. The zones of the fast increase of charge occured at higher pH's for deeper horizons, enriched with fulvic acids. The ob served changes of organic matter charge due to liming were related to the increase of fulvic to humic acids ratio. The negative charges of o rganic matter in limed and unlimed profiles estimated for high pH were better correlated with fulvic to humic acids ratio than when estimate d for lower pH levels.