ABSTRACT
Tropical and subtropical acidic soils have been well documented as hotspots of global soil nitrogen (N) oxide (i.e., nitrous oxide (N2O) and nitric oxide (NO) emissions). While the effectiveness of possible mitigation options has been extensively examined in croplands, little is known about their effectiveness in reducing N‐oxide emissions from acidic soils of rapidly expanding tea plantations in China. Here, we conducted a 2‐year field experiment to investigate how organic substitution for synthetic fertilizer and biochar amendment affect soil N‐oxide emissions from a subtropical tea plantation. Across the 2‐year measurement period, full organic substitution for synthetic fertilizer significantly increased N2O emissions by an average of 17% while had a lower NO emission compared to synthetic fertilizer alone. Our global meta‐analysis further revealed that full or partial organic fertilizer substitution resulted in a 29% (95% confidence interval: 5%–60%) increase of N2O emissions from acidic soils. In contrast, irrespective of fertilizer type, biochar amendment significantly reduced N2O emissions by 14% in the first but not second experimental year, suggesting a transient effect. The trade‐off effect of full organic substitution on N2O and NO emissions may be attributed to the favorable conditions for N2O production due to the stimulated activity of nitrifiers and denitrifiers. The suppression of N2O emission following biochar amendment was probably due to promoted further reduction of N2O to dinitrogen. The fertilizer‐induced emission factor (EF) of N2O (2.1%) in the tea plantation was greater than the current IPCC default value, but the EF of NO (0.8%) was comparable to the global estimate. Taken together, while biochar amendment could have mitigation potential, cautions are needed when applying organic substitution for synthetic fertilizer as mitigation options for acidic soils as hotspots of N‐oxide emissions.