Submitted to: Agronomy Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: 10/19/1998
Publication Date: N/A
Citation: N/A Interpretive Summary:
Technical Abstract: Humic substances (HS) are gross mixtures arising from transformations of plant and animal residues. No theory with regard to the sizes, shapes, compositions, and considerations of structures has general acceptance. Humic acids (HAs), fulvic acids (FAs) and XAD-4 acid fractions were isolated from paired (grassland/arable; forested/deforested) sites. Each extract was exhaustive at pH 7, pH 10.6, and pH 12.6, and selected fractions were subjected to elemental, sugar, and amino acid analyses, to FTIR, ESR, UV, fluorescence, to sequential chemical degradation processes (and analyses of the digest products), to NMR spectroscopy, and were titrated. Cross polarization magic angle spinning (CPMAS) **13C NMR provided valuable compositional information. The most useful structural information from spectroscopy measurements was provided by two-dimensional (2-D) liquid state NMR obtained using 500 MHz instrumentation. Several identifiable cross peaks in these (2-D) spectra gave indications of molecular compositions and connectivities, and these were most readily identifiable in cases of samples isolated at the higher pH values and representing HS related to the source plant materials. Identifications of digest products, and considerations of degradation mechanisms, gave useful information about component molecules.