ARS | Publication request: Mobile humic acids and recalcitrant calcium humate in eight US soils

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: April 20, 2009
Publication Date: July 6, 2009
Citation: He, Z., Honeycutt, C.W., Ohno, T., Mao, J. 2009. Mobile humic acids and recalcitrant calcium humate in eight US soils. Meeting Abstracts; page 151.

Technical Abstract: Both excitation-emission matrix (EEM) fluorescence spectroscopy and solid state C-13 nuclear magnetic resonance (NMR) spectroscopy have been applied for studying soil organic matter (SOM), but rarely have both techniques been employed together. We analyzed the fluorescence features of water extractable organic matter (WEOM), mobile humic aicds (MHA) and recalcitrant calcium humates (CaHA) prepared from eight US soils. EEM analysis revealed a four-component model, where component 1 was "fulvic like" and components 2 and 3 were "humic like". The unknown component 4 as highest in the water extractable organic matter fraction. All eight MHA and five CaHA samples were further analyzed by C-13 NMR spectroscopy. This analysis indicated that the two peaks at 0-50 (alkyls) and 50-60 ppm (OCH3 and NCH) were negatively correlated with peaks at 108-145 (aromatics), 145-161 (aromatic C-O) and 162-190 ppm (N-C=O and COO). Furthermore, the two peaks at 0-50 and 50-60 ppm were postively correlated with fluorophore component 4, while peaks at 145-162 and 162-190 ppm were negatively correlated with fluorophore component 4. This research indicates that combining both spectroscopic techniques enhances structural information for more fully characterizing soil organic matter.