Reduced fertilization mitigates N2O emission and drip irrigation has no impact on N2O and NO emissions in plastic-shed vegetable production in northern China

Plastic-shed vegetable production in China creates hotspots for emission of the potent greenhouse gas nitrous oxide (N2O) and the atmospheric pollutant nitric oxide (NO). To mitigate N2O and NO emissions, determination of the predominant processes of N2O and NO generation in plastic-shed vegetable production is important. Here, we reported the findings of a 2-year experimental study on the effects of reduced fertilization and/or drip irrigation on N2O and NO emissions during plastic-shed tomato production in northern China. Five treatments were applied: 1) over fertilization and flood irrigation (conventional practice); 2) fertilization reduced by 20% and flood irrigation; 3) fertilization reduced by 20% and drip irrigation; 4) fertilization reduced by 30% and drip irrigation, and 5) control (no fertilizer input and flood irrigation). Reduced both basal and top-dressed fertilization maintained tomato yields. Compared with conventional practices (mean annual N2O and NO emissions: 18.1 ± 1.3 and 0.79 ± 0.02 kg N ha-1 yr -1, respectively), fertilization reduction by 20%-30% decreased the annual N2O emission by 21.2%-27.0% owing to lower soil inorganic nitrogen (SIN) contents under the reduced fertilization practices. Switching from flood to drip irrigation might weaken denitrification due to lower soil moisture and less wet soil area, but increased SIN contents, and thus had no significant impact on annual N2O and NO emissions. Peak N2O fluxes occurred at soil temperature 28 °C and water-filled pore space (WFPS) > 60%, were higher than those for NO, and peak NO fluxes appeared 4-6 days later than N2O fluxes, consistent with the decline in WFPS. These observations indicated that N2O and NO from alkaline plastic-shed soil may be mainly generated via heterotrophic denitrification and nitrification, respectively. Reduced fertilization and drip irrigation in plastic-shed tomato production maintained crop productivity and mitigated N2O emission. These results could be integrated into the decision-making in sustainable plastic-shed production.