Half-organic substitution combined with dicyandiamide (DCD) reduces N2O and NO emissions from tea plantations: a field study and global assessment.

Acidic tea plantation soils with high nitrogen (N) inputs are recognized hotspots for nitrous oxide (N2O) and nitric oxide (NO) emissions. However, field evidence on the combined effects of organic manure and a nitrification inhibitor (dicyandiamide, DCD) on both gases remains scarce, and previous global budgets have considered N2O only, leaving combined NO + N2O unquantified. Here, a replicated field experiment using static closed chambers was conducted in a subtropical tea plantation. Seven treatments were established: urea (CN), composted chicken manure (OM), and their 1:1 combination (HOM), each applied at the same N rate with or without DCD, plus an unfertilized control. Compared with CN, the application of chicken manure alone (OM) significantly increased annual N2O and NO emissions by 17.8% and 21.4%, respectively, while HOM did not significantly affect N2O emissions but increased NO emissions by 11.4%. Relative to the corresponding non-DCD treatments, DCD application reduced N2O by 10.4% and NO by 15.5% under CNI, and reduced N2O by 26.8% and NO by 21.3% under HOMI. Overall, compared with CN, the HOMI treatment achieved the lowest combined NO + N2O emissions, achieving a reduction of 21.8%. Compilation of a worldwide database of NO and N2O emissions from tea plantations resulted in 139 and 53 measurements, respectively, which were then used to establish an empirical model for estimations of NO and N2O emissions using the application rate of fertilizer N. Accordingly, the estimated annual emissions of NO, N2O, and combined NO + N2O emissions from global tea plantations amounted to 30.5 Gg NO-N, 57.3 Gg N2O-N, and 87.8 Gg N, respectively. Scenario-based upscaling indicates that global adoption of the HOMI strategy could reduce N2O emissions by 11.8 Gg N yr-1, NO emissions by 2.98 Gg N yr-1, and combined NO + N2O emissions by 15.5 Gg N yr-1 relative to the conventional synthetic N baseline from tea plantation systems.