[Effects of biochar combined with nitrification/urease inhibitors on soil active nitrogen emissions from subtropical...

We examined the effects of biochar and urease inhibitors/nitrification inhibitors on nitrification process, ammonia and N₂O emission in subtropical soil, and determined the best combination of biochar with nitrification and urease inhibitors. This work could provide a theoretical basis for the mitigation of the negative environmental risk caused by reactive nitrogen gas in the application of nitrogen fertilizer. A indoor aerobic culture test was conducted with seven treatments [urea+biochar (NB), urea+nitrification inhibitor (N+NI), urea+urease inhibitor (N+UI), urea+nitrification inhibitor+urease inhibitor (N+NIUI), urea+nitrification inhibitor+biochar (NB+NI), urea+urease inhibitor+biochar (NB+UI), urea+nitrification inhibitor+urease inhibitor+biochar (NB+NIUI)] and urea (N) as the control. The dynamics of soil inorganic nitrogen content, N₂O emission and the volatility of ammonia volatilization were observed under combined application of biochar with urease inhibitor (NBPT)/nitrification inhibitor (DMPP). The results showed that:1)Compared to the control (5.11 mg N·kg^-1·d^-1) during the incubation period, NB treatment significantly increased therate constant of nitrification by 33.9%, and N+NI treatment significantly reduced the nitrification rate constant by 22.9%. NB treatment significantly increased the abundance of ammonia oxidizing bacteria (AOB) by 56.0%. 2) Compared with N treatment, N+NI and NB+NI treatments signi-ficantly enhanced the cumulative emission of NH₃ by 49%. The N+UI treatment reduced the cumulative loss of NH₃. The inhibition effect of NB+UI treatment was more significant. 3) The emission rate of N₂O was highest in the first 10 days after fertilization. The N₂O emission under NB treatment was the earliest, and that of N treatment was the highest (5.87 μg·kg^-1·h^-1). The combined application of DMPP and NBPT performed the best in reducing soil N₂O emission. We estimated global warming potential (GWP) of the direct N₂O and indirect N₂O (NH₃) emissions. Compared with N treatments, N+NI and NB+NI treatments increased the GWP by 34.8% and 40.9%, respectively. While the NB and NB+UI treatments significantly reduced the GWP by 45.9% and 60.5%, the combination of biochar and urease inhibitor had the best effect on reduction of GWP of soil active nitrogen emissions.