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The optical characterization of the organic matter (OM) of an Andisol obtained from selective and sequential extractions of Al, Fe and Si (potassium chloride, sodium pyrophosphate, ammonium acid oxalate, dithionite-citrate-bicarbonate and sodium hydroxide) was made. From the absorbances the E4/E6 ratio, the Δ log K, the Melanic Index (MI) and the ODOE were calculated. The behaviors of the E4/E6 ratio, the Δ log K and the MI in the extracts obtained with sodium pyrophosphate and with ammonium acid oxalate showed a higher degree of humification for the organic matter extracted from the A and 2B/A horizons and one smaller for the one extracted from the 3C/A and 4Bs horizons. The ODOE showed the presence of organic complexes in the extracts obtained with pyrophosphate and with sodium hydroxide and the iluvial accumulation of non-crystalline Fe oxides and hydroxides in the 4Bs horizon in the extract obtained with ammonium acid oxalate. In the horizon A, the humification indexes marked a change in the degree of evolution of the MO between 8 and 10 cm of depth, which could indicate the presence of a lithological discontinuity or of buried soil.

Caracterización óptica de la materia orgánica de un Andisol del Oriente antioqueño, Colombia