Soil organic matter (SOM) can be defined as a fraction of soil that consists of plants, animals and microbial deposits at different stages of decomposition.  Soil organic matter is one of the significant carbon pools in the biosphere.  At least 50% of soil organic carbon is composed of humic substances that can be divided into three fundamental fractions:  humic acids (HA), fulvic acids (FA) and humin. Humic substances are complex and heterogeneous mixtures of polydispersed materials formed by biochemical and chemical reactions that may further react, decay and transform to other products.  Despite intensive research on humic substances using various spectroscopic techniques in the past decade, the chemical structures of HA and FA are not fully understood.  The use of modern analytical equipment is an essential condition for more sophisticated structural interpretations of humic substances.  Nuclear magnetic resonance (NMR) is one of the most widely used and powerful tools for structural studies. Solid state 13-C Cross Polarization and Magic Angle Spinning NMR spectra of HA extracted from native prairies and prairie restoration sites were determined using a Tecmag 360 NMR system operated at 363 MHz with a 7mm CPMAS duty probe.  Humic substances were extracted from soil utilizing strong base. All HA samples from native prairies, prairie restorations and the controls showed similar functional moieties in the 13C-NMR spectra. The major difference observed was with respect to peak intensity among spectra. Cross Polarization and Magic Angle Spinning 13C-NMR spectra characterization of HA from native prairie and prairie restorations did not show any exceptional differences in the alkyl region.

Soil organic matter in native prairies and prairie restorations III:  Structural studies of humic acids with carbon-13 NMR spectroscopy

255th National Meeting (2018)

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