Nitrogen-loaded biochar for environmental management: Enhancing nitrogen utilization balance in farmland, mitigating ammonia volatilization, and improving fertilizer efficiency

Although biochar was widely applied to improve crop yield, it can also trigger increased ammonia volatilization, thereby deteriorating the environment of rice paddies. Therefore, to continuously supply available nitrogen (N) and mitigate ammonia volatilization in rice fields, a two-year field experiment was conducted with nitrogen-loaded biochar (NLB) combined with less N fertilizer. The treatments included 10 or 20 t·ha −1 NLB+ 100 % urea (T1, T2); 10 or 20 t·ha −1 NLB+ 75 % urea (T3, T4); and a control with 100 % urea without NLB (CK). Results indicated the ammonia volatilization accumulation of T3 and T4 treatments was significantly reduced by 13.30–20.96 % compared to CK treatment. T2 treatment significantly increased rice yield by 6.94–11.15 % and 1000-grain weight by 9.78–11.59 %, while the T4 treatment maintained rice yield, due to NLB effectively N compensating and promoting the formation of 1000-grain weight and panicle numbers. Under T4 N management, crop growth and yield were promoted primarily because stable N release better matched the N demands of rice plants in later growth stages. The slow-release N persisted over 30 days in the later stages, increasing soil NH 4 + -N by 13.72 %. The N nutrition index (NNI) of T2, T3, and CK was far from 1, while T4’s NNI was close to 1, indicating that T4 provided an optimal N supply. In conclusion, the combination of NLB and 75 % N fertilizer effectively mitigated ammonia volatilization in rice paddies and maintains yield stability. This study provided a benefit guidance for agricultural environmental protection in Northeast China. • NLB can effectively replace 25 % urea. • NLB coupled with 75 % N fertilizer mitigated ammonia volatilization by 13.30–20.96 %. • NLB slowly released N over 30 days, matching the N demands of rice plants well at late stages. • NLB with 75 % N fertilizer decreased ammonia volatilization and increased yields by improving N utilization balance.