15N and 13C CPMAS spectra of composted plants are presented. The plants (L. rigidium and Zea mays) were grown in 15N enriched medium and fennented for several months until an approx. 80% of the dry matter was lost. In all 15N spectra the secondary amide/peptide peaks a 87 ppm contributes more than 80% of the total intensity. No new 15N peaks are formed during the fermentation process. Older attempts to assign a significant fraction of humic acid nitrogen to heteroaromatic structures formed in the fermentation process are thus most probably wrong.