Annual NO and [N.sub.2]O emissions under different fertilisation regimes from a greenhouse vegetable cropping system in subtropical China

Context. Overuse of N fertiliser in vegetable cropping systems is known to release of nitric and nitrous oxide to the atmosphere in China. Optimisation of N fertilisation regimes has the potential to mitigate NO and [N.sub.2]O emissions from these N-rich systems. Aims. We investigated the effects of different N fertilisation regimes on NO and [N.sub.2]O emissions, and vegetable yields, with particular efforts to estimate annual direct emission factors of NO and [N.sub.2]O under different N fertilisation regimes in greenhouse vegetable fields. Methods. Annual NO and [N.sub.2]O fluxes were taken simultaneously using the static chamber-based method from a greenhouse vegetable system in south-east China with four N fertiliser treatments: (I) no N fertiliser (control); (2) chemical N fertiliser application (CF); (3) organic N fertiliser application (OF); and (4) organic-chemical mixed N fertiliser application (MF). Key results. N fertilisers significantly increased NO and [N.sub.2]O emissions. Direct emission factors of N fertiliser for NO and [N.sub.2]O were the largest for MF, with an average of 0.99% and 0.67%, respectively. Vegetable yields were only significantly enhanced under OF treatment. Conclusions. Relative to the use of chemical N fertiliser, the application of organic-chemical mixed N fertiliser showed not to be effective for mitigating NO and [N.sub.2]O emissions. Instead, sole application of organic N fertiliser was a viable option to enhance vegetable yields but without increasing NO and [N.sub.2]O emissions in greenhouse vegetable systems. Implications. Substituting the use of chemical N fertiliser with organic N fertiliser input could benefitvegetable production but without stimulating NO and [N.sub.2]O emissions from vegetable cropping systems in sub-tropical China. Keywords: emissions factor, greenhouse vegetable field, nitric oxide, nitrous oxide, NO/[N.sub.2]O ratio, organic fertiliser, vegetable yields, WFPS.
Introduction Nitric (NO) and nitrous oxide ([N.sub.2]O) are two trace gases that play critical roles in global nitrogen cycle. Both NO and [N.sub.2]O are involved in atmospheric photochemistry processes and [...]