Co-application of nitrification inhibitors with straw or biochar yielded varying effects on soil nitrification rate, N2O emissions, and ammonia oxidizers

Purpose Nitrification inhibitors (NIs) are effective in reducing nitrification rates and nitrogen environmental losses. Yet, the combined effects of NIs with straw or biochar on soil nitrification and nitrous oxide (N2O) production remain unclear. Materials and methods In this study, we performed an aerobic N-15 microcosm incubation experiment to compare the effects of a biological nitrification inhibitor (methyl 3-(4-hydroxyphenyl) propionate, MHPP) and a synthetic nitrification inhibitor (3,4-dimethylpyrazole phosphate, DMPP), both in combination with straw or biochar, on gross N nitrification rates and N2O production rates. Results and discussion DMPP and MHPP significantly reduced gross nitrification rates by 54.7% and 31.2%, respectively. Sole biochar application increased soil nitrification rates 1.2 times while having a negligible impact on short-term N2O emissions. The co-application of nitrification inhibitors with biochar mitigated the stimulatory effects on nitrification. Straw inhibited nitrification slightly and stimulated N2O emission significantly (p < 0.05), while co-application of DMPP and MHPP enhanced the inhibitory effect on nitrification by 41.4% and 62.3%, as well as reduced higher N2O emission. Nitrification inhibitors inhibited the abundance of the amoA gene in both ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB), and the communities of AOB were more sensitive to nitrification inhibitors than AOA. Conclusion Our findings indicated that combining nitrification inhibitors with straw or biochar can synergistically affect soil nitrification and N2O emissions. Biochar co-applicated with DMPP showed the most significant effect on inhibiting nitrification and N2O production, positively influencing soil inorganic N retention.