Resumo

AVELLANEDA, Lizeth Manuela; LOZANO DE YUNDA, Amanda  e  ZAMUDIO, Adriana Mireya. EFFECT OF THE USE AND THE COVER OF THE SOIL ON THE PROFILE OF POLYDISPERSITY OF HUMIC ACIDS EXTRACTED OF AN ANDISOL FROM THE DEPARTMENT OF CALDAS,COLOMBIA. Rev.Colomb.Quim. [online]. 2005, vol.34, n.2, pp.189-200. ISSN 0120-2804.

In order to know the possible effect of the use and the cover of soil, on the polydispersity profile of humic acids were analyzed the A horizon of three samples of an andisol (Melanudand) from the Department of Caldas, Colombia, that have presented different management and coverland as soils under forest of bamboo, coffee with somber of guamo and under free exposition coffee. For this in the lower fraction to 50 µm, the sequential extraction of humic substances was carried out with solutions of sodium tetraborate (Na₂B₄O₇ 0.05 M), sodium pyrophosphate (Na₄P₂O₇ 0.025 M) and sodium hydroxide (NaOH 0.1M) and the later separation and purification of the respective humic acids. To obtain the polydispersity profiles was applied the exclusion chromatography separation by size technique utilizing Sephadex G-75 and ultracentrifugation by gradient of density with sucrose and they devised graphics of distribution by size (absorbance (450 nm) vs. volume eluted). It was found that the humic acids extracted with sodium hydroxide presented smaller polydispersity, bigger size and molecular weight, as well as, degree of aromatic condensation. The results did not show drastic effect of the use and the coverland , on the polidispersity profile and the coefficient of sedimentation of the humic acids, which is related to the size, weight and molecular density of the same ones. Nevertheless, it was found that the húmic acids of the samples of soil under coffee with somber of guamo and free exposition coffee are very similar among it and different from the sample under forest of bamboo. This fact was associated with a beginning of the effect of the use and the cover of the soil on the size of the humic acids. It presumed that in the long term the effect is accentuated and eventually could be considered as indicator of degradation of the organic component of the soil.

Palavras-chave : andisol; humic acids; size exclusion chromatography (SEC); gradient density centrifugation (GDU); coverland.

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