Effects of the nitrification inhibitor DMPP (3,4-dimethylpyrazole phosphate) on gross N transformation rates and N₂O emissions

Many studies have shown the efficiency of the nitrification inhibitor 3,4-dimethylpyrazole phosphate (DMPP) in suppressing nitrification and nitrous oxide (N2O) emissions. However, the effect of DMPP on soil gross nitrogen transformations and the mechanism of its inhibitory effects on N2O production pathways remain unknown. A 15N tracing experiment was conducted to investigate the effect of DMPP on gross N transformation rates and pathways of N2O production in two typical Chinese and UK agricultural soils. The soils differed in organic carbon (C) and clay content but otherwise had similar properties. The results showed that the application of DMPP decreased the gross autotrophic nitrification rate (p < 0.05) by 21.6% in the Chinese soil and 9.4% in the UK soil. The lower inhibitory efficiency of DMPP in the UK soil was likely to have been due to high rates of adsorption by soil organic C and clay. The total gross rate of mineralization was lower in the presence of DMPP in both soils, likely because there was a regulatory feedback when ammonium concentrations were high. DMPP also significantly reduced cumulative N2O emissions (p < 0.05) in both soils (by between 15.8 and 68.4%), which might be attributed to the dual inhibitory effect of the DMPP on autotrophic nitrification rate and the proportion of N2O produced by autotrophic nitrification processes. This finding will help to predict the sites where DMPP is likely to be most effective and allow the user to target DMPP application to soils with particular properties.