EFFECT OF THE CHEMICAL COMPOSITION OF SOIL HUMIC ACIDS ON THEIR VISCOSITY, SURFACE PRESSURE, AND MORPHOLOGY

Humic acids were extracted from two histosols, an andosol, an inceptisol, a rice field soil, and a sludge-amended cambisol and characterized by elemental analysis, acidic groups titration, E4/E6 determination, Fourier transform infrared (FTIR) and 13C nuclear magnetic resonance (13C NMR) spectroscop