The ammonium amendment (8 mmol/kg soil) significantly inhibited the degradation (half-life of 68.0 7.7 days), mineralization (2.0 1.1%),and bound-residue formation (23.7 0.2%). Under anoxic conditions, 4-NP111 did not degrade during 49 days of incubation and the ammonium amendment (40 mmol/kg soil) did not affect its persistence.