@article{articlec391978e,
title   = {Humic acids from hydromorphic soils of the upper Negro river basin, Amazonas: Chemical and spectroscopic characterisation},
author = {Mafra, A. L. and Senesi, N. and Brunetti, G. and Miklós, A. A. W. and Melfi, Adolpho José},
year = {2007},
doi = {10.1016/j.geoderma.2006.11.005},
journal   = {Geoderma}
}