Solid-state ¹³C-NMR spectroscopy proved that the plowing and burial of soils resulted in a decrease in aliphatic carbon content and in a relative accumulation of carbon in the aromatic structures of humic acid molecules. The Fourier transformation of ¹³C-NMR spectra of humic acids from both chernozem and dark gray forest soil permitted the author to identify the highly condensed aromatic carbon compounds in the spectral peak corresponding to aromatic carbon.