Evidence for the Existence of Humic Acids in Peat Soils Based on Solid‐State 13C NMR

Humic extracts, in particular humic acids, of organic‐rich peat soils were examined by solid‐state 13C nuclear magnetic resonance (NMR) and shown to be integral components of the peat, contrary to recent suggestions that humic materials are artifacts of alkali extraction. The authenticity of humic substances is demonstrated by recombining the various humic fractions and comparing the NMR spectrum of the recombined peat with the original untreated peat sample. Even though significant NMR‐determined structural differences exist between humic acids and the insoluble humin fractions, the recombination reproduces the original unextracted peat quite well. Applying a biopolymer mixing model to the spectra shows that humic acids have a high proportion of char‐like material that is interpreted as being derived from noncombustion polymerization or secondary synthesis during humification, a process that has been challenged by a recent soil formation model. Core Ideas Solid‐state 13C NMR of soils isolated by dilute alkali proves the existence of humic acids. Molecular mixing model and physical reconstitution both confirm the alkali extracts are real. More char‐like structures in humic acids than humin suggests secondary synthesis formation.