Simultaneous quantification of greenhouse gas and nitric oxide emissions from subtropical conventional vegetable systems: a 2-site field case study in Sichuan Basin

Abstract

Quantification of greenhouse gases [nitrous oxide (N2O) and methane (CH4)] and nitric oxide (NO) emissions from subtropical conventional vegetable systems through multi-site field measurements are needed to obtain accurate regional and global estimates. N2O, NO and CH4 emissions from subtropical conventional vegetable systems were simultaneously measured at two different sites with hilly topography in the Sichuan basin, southwest China by using the static chamber gas chromatography technique. Results showed that annual soil N2O and NO fluxes for the treatment receiving N fertilizer ranged from 6.34–7.71 kg N ha−1 yr−1 and 0.69–0.85 kg N ha−1 yr−1, respectively, while decreased soil CH4 uptakes by 26.4% as compared with no N fertilizer addition across our two sites of experiment. Overall, the average direct N2O and NO emission factor (EFd) were 0.71% and 0.12%, respectively, which were both lower than the available EFd for subtropical conventional vegetable systems. This finding indicates that current regional and global estimates of N2O and NO emissions from vegetable fields are likely overestimated. Background N2O emissions (3.42–3.62 kg N ha−1 yr−1) from the subtropical conventional vegetable systems were relatively high as compared with available field measurements worldwide, suggesting that background N2O emissions cannot be ignored for regional estimate of N2O emissions in subtropical region. Nevertheless, the significantly intra- and inter-annual variations in N2O, CH4 and NO emissions were also observed in the present study, which could be explained by temporal variations of environmental variables (i.e. soil temperature and moisture). The differences in N2O and NO EFd and CH4 emissions between various vegetable systems in particular under subtropical conditions should be taken into account when compiling regional or global inventories and proposing mitigation practices.