Influence of Extractant and Soil Type on Molecular Characteristics of Humic Substances From Two Brazilian Soils

Abstract

Num estudo anterior, observou-se que substâncias húmicas (HS) extraídas com solução de NaOH e com solução de Na4P2O7 apresentaram diferentes pesos moleculares, e que o rendimento de HS extraídas por cada método variou entre um Oxisol e um Mollisol do Sul do Brazil. No presente trabalho, o estudo da matéria orgânica nestes solos foi continuado, através da caracterização das HS extraídas com solução de NaOH 0.5 mol L -1 e com solução neutra de Na4P2O7 0.15 mol L -1 das amostras acima mencionadas, empregando-se análise elementar e espectroscopia de ressonância magnética nuclear ( 1 H-and 13 C-NMR no estado líquido). As diferenças moleculares foram relacionadas com o método extrator e com o tipo de solo. HS extraídas com pirofosfato foram mais humificadas, apresentando caráter aromático e proporção de grupos carboxílicos superiores. As HS extraídas com NaOH foram mais alifáticas e continham uma maior proporção de grupos O-alquila, o que é indicativo de um natureza menos humificada do que as HS extraídas com pirofosfato.In a previous study it was observed that humic substances (HS) extracted with NaOH solution and with Na4P2O7 solution presented different molecular weights, and also that the extracted HS yield by each method varied between an Oxisol and a Mollisol from South Brazil. In the present study, we further investigated the organic matter in these soils by characterizing HS extracted with 0.5 mol L -1 NaOH and with neutral 0.15 mol L -1 Na4P2O7 solutions from the above mentioned samples, using elemental analysis and nuclear magnetic ressonance spectroscopy (liquid state 1 Hand 13 C-NMR), and by relating the molecular differences to the extraction method and soil type. HS extracted with pyrophosphate were more humified, showing a higher aromaticity and higher carboxylic content. The NaOH-extracted HS were more aliphatic and contained a higher O-alkyl proportion, which is indicative of a less humified nature than the pyrophosphate-extracted HS.

Characteristics of soil organic matter of different Brazilian Ferralsols under native vegetation as a function of soil depth

“…The occurrence of SOM in kaolinitic and Fe-oxides containing soil, that is richer in polysaccharides structures and poorer in aromatic groups in comparison to smectitic-associated SOM, has been reported earlier (Dick et al, 1999;Wattel-Koekkoek et al, 2001). The role of the surface complexation on Aloxides surfaces in stabilizing carbohydrates structures in SOM was also verified by Parfitt et al (1999), although they reported that the soluble complex of SOM with Al 3+ ions did not present this protective effect.…”

Distribution of chemical compartments of soil organic matter and c stocks of a cambisol from south Brazil as affected by Pinus afforestation

“…21 The calibration curve was prepared with 6 solutions of D-fructose with concentrations ranging from 0 to 200 mg C L -1 . The amount of C contained as humic acid (C HA ) was calculated by the difference: C EHS -C AF .…”

Substâncias húmicas de turfa: estudo dos parâmetros que influenciam no processo de extração alcalina

“…Ainda não existe uma metodologia para extração de SH de solos, oficialmente adotada. Alguns autores têm utilizado extratores mais brandos como pirofosfato de sódio 15 , agentes complexantes 16 , ácido fórmico 17 , misturas ácidas 18 e solventes orgânicos 19 . Mesmo havendo risco de alterações estruturais, outros autores preferem a extração mais completa das SH utilizando álcalis 1,2 .…”