SOME CHARACTERISTICS OF HUMIC MATERIALS IN CARIBBEAN VERTISOLS

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Abstract
A comparative investigation of the analytical features of organic matter fractions of acidic and calcium-saturated Vertisols (Ca-Vertisols) from the Caribbean was undertaken. The elemental composition and functional group content of the humic acids (HAs) and fulvic acids (FAs) were similar to previously reported values, except for the low yielding HAs of Ca-Vertisols which contained a greater proportion of O (35.82–47.17%). In addition, high values (8.38 meq/g–11.71 meq/g) for the COOH functional groups of the FAs emphasized the inherent high reactivity of the humic materials. Spectrophotometric analysis supported the view arrived at through chemical analysis that metal-organic (FA) complexes of Vertisols contained Al, Fe and Si with more soluble complexes in the Ca-Vertisols and in the presence of a basic cation (Ca). DTA analysis indicated that the organo-mineral complexes of Vertisols were regular and thermostable. Key words: Vertisols, humic materials, functional groups, infrared, DTA

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