Objectives The application of nitrification inhibitors (NIs) is an effective measure to suppress soil nitrification and reduce nitrogen losses in agricultural ecosystems. However, the efficacy of NIs is influenced by both types of NIs and fertilization management practices. Further investigation is urgently required to elucidate the inhibitory effects of NIs on soil nitrification and underlying mechanisms.

Methods An incubation experiment was conducted using red soils collected from a long-term fertilization field experiment in Jinxian, Jiangxi Province, China, including unfertilized control (Control), mineral fertilizer (NPK), organic fertilizer (OM), and combined mineral and organic fertilizer (NPKM) treatments. Three nitrification inhibitor treatments were established for each soil: no nitrification inhibitor (NoNI), the biological nitrification inhibitor methyl 3-(4-hydroxyphenyl) propionate (MHPP), and the chemical nitrification inhibitor 3,4-dimethylpyrazole phosphate (DMPP). Soil physicochemical properties were determined before incubation, and soil samples were collected on days 0, 1, 3, and 6 to measure NH₄⁺-N and NO₃⁻-N contents. Net nitrification rate, nitrification inhibition rate, and their relationships with soil properties were analyzed.

Results Compared with NoNI, MHPP treatment reduced the net nitrification rates of the Control, OM, and NPKM treatment soils by 62.04%, 59.57%, and 39.73%, respectively, with nitrification inhibition rates remaining above 40%, and higher than that of DMPP; DMPP treatment reduced the net nitrification rates by approximately 60% and 40% in the OM and NPKM treatments, with inhibition rates of about 60% and 40%, respectively, but showed no significant inhibitory effect in the Control and NPK treatments. Both inhibitors delayed NH₄⁺-N transformation and reduced NO₃⁻-N accumulation, although their inhibitory effects were significantly regulated by fertilization regimes. Correlation analysis indicated that the inhibitory effect of MHPP was mainly associated with soil C:N and pH, whereas the effectiveness of DMPP was more strongly related to soil pH and organic carbon content.

Conclusions Long-term fertilization altered soil pH, organic carbon content, and C:N ratio, thereby affecting the performance of nitrification inhibitors in red soils. Under organic fertilizer and combined organic–mineral fertilizer systems, both MHPP and DMPP effectively suppressed nitrification, with MHPP showing more stable inhibitory performance. In contrast, DMPP was more suitable than MHPP in soils receiving only mineral fertilizer.