Abstract:This study aimed to investigate the effects of rice straw-derived biochar application on rice grain yield, nitrogen use efficiency (NUE), and fate of fertilizer N. A pot experiment was conducted to assess the effects of rice straw-derived biochar application on rice biomass, N accumulation, as well as fate of urea-N using 15N tracing method and ammonia oxidizers. Five treatments were included:no N application (N0), chemical fertilizer application only (CF), CF+0.5% biochar (BC1), CF+1% biochar (BC2), and CF+2% biochar (BC3). The results showed that BC2 and BC3 treatments significantly increased rice grain yield by 19.3% and 22.0%, compared to CF treatment, respectively. Application of biochar significantly enhanced the N accumulation of rice and N apparent use efficiency compared to CF treatment. The fertilizer N uptake by grain and rice plant was 18.6%~23.4% and 18.5%~26.5% greater in biochar application than in CF treatment, respectively. While, no significant difference was observed in the soil N uptake by grain between BC treatments (BC1, BC2, and BC3) and CF treatment. The 15N use efficiency was 30.4%, 28.5%, and 29.3% in the BC1, BC2, and BC3 treatments, respectively, which were all significantly higher than that in CF treatment (24.1%). Application of straw-derived biochar increased the fertilizer N residual in soil and reduced the N loss, compared to CF treatment. Thus, the ratio of fertilizer N loss was greatly lower in BC treatment (25.7%~27.5%) than in CF treatment (38.4%). Higher application of biochar (BC3) significantly decreased the AOB amoA gene copies, compared to CF treatment. While, no significant difference was found in AOA abundance between the BC and CF treatments. Overall, application of rice straw-derived biochar is an effective practice to increase rice yield and NUE, and reduce the N loss in the rice production.