Abstract
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.