Abstract A new role for nitrification in soils, i.e. binding of mineral nitrogen on soil organic matter, and thus formation of soil organic nitrogen, is proposed. Nitrogen balance and 15 N data are presented which substantiate the hypothesis that nitrification, even at neutral pH conditions, mediated the nitrosation of aromatic structures. Thus, nitroso- and nitro-compounds were formed and transiently detectable. Concomitantly, a transient decrease of soil ATP and microbial biomass was observed. These findings implement the need for an in-depth analysis of side-effects of nitrification in organic matter-containing ecosystems.