AbstractChemical distribution patterns were obtained for the residual N in field plots previously amended with 15N‐labeled urea and oxamide. From 25 to 40% of the fertilizer N was present in the soil (0 to 25 cm) after the first growing season, about half of which still remained after 5 years. Essentially all of the fertilizer‐derived N (97.0%) occurred in organic combination; only a small fraction (3.0%) was accounted for in inorganic forms, chiefly as fixed NH4+. In comparison to the native humus N, higher percentages of the fertilizer N left after the first growing season occurred as amino acids (52.0 vs. 33.7%) and amino sugars (8.2 vs. 7.5%); lower percentages occurred in acid‐insoluble forms (9.0 vs. 15.2%), as acid‐hydrolyzable organic NH3 (9.0 vs. 17.0%), and as unidentified acid‐soluble N (8.8 vs. 20.3%). Considerable humification occurred during the subsequent 4 years with relocation of amino acids N (and possibly amino sugar‐N) to more resistant humus forms. The findings suggest that fertilizer N, once incorporated into soil organic matter, becomes increasingly stable with time and is not readily mineralized or subject to leaching.