The effect of nitrification inhibitors in reducing nitrification and the ammonia oxidizer population in three contrasting soils

PURPOSE: 3,4-Dimethylpyrazole phosphate (DMPP) and acetylene (C₂H₂) are widely used nitrification inhibitors. These nitrification inhibitors have shown inconsistent efficacy in different soils, demonstrating the importance of determining which soil and microbial factors cause this variability. The aim of the present study was to investigate the efficacy of DMPP and C₂H₂to inhibit nitrification and the ammonia oxidizer population in three contrasting soil types from Australia. MATERIALS AND METHODS: Three contrasting soils of different pHWₐₜₑᵣ(4.6, 7.0, and 8.0) collected from different agriculture systems in Australia were used in a laboratory incubation experiment for 28 days to compare the efficacy of DMPP and C₂H₂to inhibit nitrification. We measured mineral nitrogen (N) concentrations during the incubation. In addition, quantitative PCR was applied to quantify the ammonia oxidizer population and to investigate the population change in response to DMPP and C₂H₂addition. RESULTS AND DISCUSSION: Acetylene completely blocked nitrification in the three soils while DMPP was more effective in inhibiting nitrification in the neutral soil (93.5 %) than in the alkaline soil (85.1 %) and acid soil (70.5 %). Ammonia-oxidizing archaea (AOA) were more abundant than ammonia-oxidizing bacteria (AOB) in all three control soils, with the highest AOA abundance found in the acid soil. The addition of DMPP and C₂H₂significantly decreased AOA abundance in all soils (P < 0.05) and significantly suppressed AOB abundance in the neutral soil and slightly blocked AOB growth in the alkaline soil, though it had no effect on AOB abundance in the acid soil. CONCLUSIONS: Our results show C₂H₂completely inhibited nitrification and performed better than DMPP in our study. DMPP was more effective in the neutral soil than other two soils. Neither DMPP nor C₂H₂was a selective nitrification inhibitor in neutral and alkaline soils in which both AOA and AOB were inhibited. Neither DMPP nor C₂H₂had any effect on AOB abundance in the acid soil. Soil pH plays an important role in the effectiveness of DMPP and C₂H₂in inhibiting nitrification and ammonia oxidizer population.