Soil samples of 50 g clay, clay loam and sandy loam were amended with ammonium sulphate giving 25, 50, 100, 200, and 400 mg nitrogen (N)/kg and with two nitrification inhibitors, Dicyandiamide (DCD) and N‐Serve (N‐S) each at two levels calculated relative to the N applied, 1 and 5%, and 0.5 and 1%, respectively. Water was added to moisture field capacity and the samples were incubated at 30°C for 7, 14, 28, and 56 days, each treatment and timing in three replicates. The lower level of application of nitrification inhibitors was not effective. Nitrate‐N (NO3‐N) recovery peaked at 28 days and did not change appreciably later, except the 1% N‐S treatments where a flush of NO3appeared at the 56th sampling day. The nitrification inhibitory effects of the two inhibitors were enhanced at the 200 and 400 mg/kg ammonium‐N (NH4‐N) application in all three soils. Nitrification inhibition was not related to salt concentrations as measured by electrical conductivity.