Abstract

ZAMBONI C, Ingrid R; BALLESTEROS G, María I  and  ZAMUDIO S, Adriana M. CHARACTERIZATION OF HUMIC AND FULVIC ACIDS FROM A MOLLISOL UNDER TWO DIFERENT COVERLANDS. Rev.Colomb.Quim. [online]. 2006, vol.35, n.2, pp.191-203. ISSN 0120-2804.

In order to determine and to compare some physicochemical properties of humic (HA) and fulvic (FA) acids such as degree of condensation and polymerization, the total C,H,N content and pKa values were analyzed in the smaller fraction (< 50 m) from Ap horizon under sugarcane crop in opposition to A horizon under forest, both Mollisol order. To carry out this aim, successive extractions with sodium tetraborate 0.05 M, sodium pyrophosphate 0.025 M, and sodium hydroxide 0.1 M were made. The purification of these humic substances by treatment with inorganic acids 1% solutions of HCl and HF, Amberlite XAD-16 adsorption resin and R 101H⁺ cationic exchange, dialysis and freeze driying were done. The humic and fulvic acids were characterized by elemental analysis, E₄/E₆ relation and acid-base potentiometry. The ratio E₄/E₆ allows to establish that molecular size and degree of condensation in humic acids were bigger than in fulvic acids. By means of acid-base potentiometry, the concentrations of functional acid groups and their acid constants in the humic and fulvic acids were determined. Four constants were found; first and second between pH 4.0 and 6.1 correspond to differents kinds of carboxyl groups and another two between pH 7.2 and 8.7 come from strong O-H phenolic and weak carboxyl groups. In the Ap horizon under sugarcane the characterization showed that the handling and land use practices promote the homogeneity of humic substances meanwhile in the A horizon under forest; the humic and fulvic acids are different due to their degree of condensation molecular size and humification index.

Keywords : Mollisol; humic acid; fulvic acid; acid-base potentiometry.

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