Advanced 13C NMR Analysis of the Light Fraction, Particulate Organic Matter, and Humic Acid Fractions From a Corn-Soybean Soil.

Fractions of soil organic matter (SOM) are usually extracted from soil by either physical (e.g., size, density) or chemical (e.g., base, acid) procedures. Integrated procedures that combine both of these types promise greater insights into SOM chemistry and function. For a corn-soybean soil in Iowa, we extracted in sequence the light fraction, two particulate organic matter fractions, and two NaOH-extractable humic acid fractions. They were analyzed by advanced 13C NMR techniques, including quantitative direct polarization/magic angle spinning, spectral-editing techniques such as dipolar dephasing, chemical-shift-anisotropy filter, CH and CH2 selection, and two-dimensional 1H-13C heteronuclear correlation NMR. Quantities of extracted SOM fractions were reproducible, and those of some fractions responded to field treatments. NMR results indicate a progressing degree of humification with successively extracted SOM fractions, with clear differences between the physical and chemical fractions. Further details will be presented.