Biochar with nitrapyrin reduces ammonia volatilization and increases nitrogen use efficiency of cabbage: A 15N tracer study.

Aim: Nitrogen use efficiency (NUE) in subtropical cropping systems is low causing a large quantity of reactive N loss to the environment. However, the mechanisms and pathways of such losses are poorly understood. The objectives of the research were to quantify N volatilization rates and corresponding NUE in a biochar and nitrapyrin-treated cabbage field using N-control as well as a ¹⁵N-based approach. Methods: The treatments consisted of: N-control, urea alone, urea with nitrapyrin (UN), urea with biochar (UB), and urea with biochar and nitrapyrin (UNB). In each plot, ¹⁵N-labeled urea was applied in 1 m² micro-plots to repeat the treatments. Results: The UNB had higher (p < 0.001) crop yields than other treatments by 29, 23 and 16% over the urea, UN and UB treatments, respectively, while the UN and UB were also higher than the urea alone. The estimated ¹⁵N-based NUE was higher (p < 0.01) in the UNB (40%) than in the urea alone (32%) but similar to the UN (36%) and UB (38%). The N-control based calculation overestimated NUE by 2–13% relative to the ¹⁵N-based approach. The UNB treatment reduced NH₃ volatilization by 37, 22, and 33% over urea alone, UB and UN, respectively (p < 0.01). Post-harvest soil organic carbon (SOC) and total N were higher (p < 0.001) in the UNB and UB treatments than the other treatments. Conclusion: Our results with a subtropical crop suggest that biochar alone or co-applied with nitrapyrin improves NUE and mitigates NH₃ volatilization while increasing SOC and TN contents. [ABSTRACT FROM AUTHOR]