Araujo, JR,Archanjo, BS,de Souza, KR,Kwapinski, W,Falcao, NPS,Novotny, EH,Achete, CA

2014

November

Biology And Fertility Of Soils

Selective extraction of humic acids from an anthropogenic Amazonian dark earth and from a chemically oxidized charcoal

Published

()

Oxidized charcoal Amazonian dark earth Soil organic matter Humic acids X-ray photoelectron spectroscopy Pyrogenic C SOIL ORGANIC-MATTER GRAPHENE OXIDE-FILMS BLACK CARBON MASS-SPECTROMETRY GRAPHITE OXIDE SPECTROSCOPY XPS IDENTIFICATION STABILIZATION SUBSTANCES

50

1223

1232

Spectroscopic techniques including X-ray photoelectron spectroscopy (XPS) can identify particular chemical groups of humic acids (HA) from "Terra Preta de Aindios" (TPI) or Amazonian dark earth, the highly fertile anthropogenic soil found in the Amazonian region. The high fertility and resilience of these soils cannot be explained by their chemically inert pyrogenic C content alone, but the natural aging of this C generates reactive carboxyl functional groups attached directly to the recalcitrant polycondensed aromatic backbone. Through spectroscopic techniques used in this work, the HA fraction (the alkaline-soluble organic matter that precipitates at low pH) of the TPI soil was compared with humic and fulvic acids, obtained by oxidizing activated charcoal with sodium hypochlorite. The yields recovery of HA-like substances was 12 and 28 wt% by using 10 and 20 cmol L-1 of oxidizing agent, respectively. X-ray photoelectron spectroscopy, energy dispersive X-ray, and solid-state C-13 nuclear magnetic resonance (C-13 NMR) spectroscopies were used to evaluate the elements and structures present in all samples. XPS C 1 s spectra of HA extracted from TPI soil and from prepared HA showed aromatic structures (C = C and pi-pi* shake-up satellite peak) bounded to carboxyl groups (COOH). The morphology and polycondensation level of aromatic C were evaluated by scanning electron microscopy (SEM). The similarities of the spectra indicated that the used method was efficient to obtain an organic amendment similar to TPI soil organic matter.

10.1007/s00374-014-0940-9