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

We examined the effects of biochar and urease inhibitors/nitrification inhibitors on nitrification process, ammonia and NO 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, NO 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·d) 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 NH by 49%. The N+UI treatment reduced the cumulative loss of NH. The inhibition effect of NB+UI treatment was more significant. 3) The emission rate of NO was highest in the first 10 days after fertilization. The NO emission under NB treatment was the earliest, and that of N treatment was the highest (5.87 μg·kg·h). The combined application of DMPP and NBPT performed the best in reducing soil NO emission. We estimated global warming potential (GWP) of the direct NO and indirect NO (NH) 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.